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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>N. X. Phuc);</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>PUXai at MentalRiskES 2025: RoBERTuito with Bidirectional LSTM for Early Gambling Disorder Detection</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Nguyen Xuan Phuc</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Dang Van Thin</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>University of Information Technology-VNUHCM</institution>
          ,
          <addr-line>Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City</addr-line>
          ,
          <country country="VN">Vietnam</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Vietnam National University</institution>
          ,
          <addr-line>Ho Chi Minh City</addr-line>
          ,
          <country country="VN">Vietnam</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2025</year>
      </pub-date>
      <volume>000</volume>
      <fpage>0</fpage>
      <lpage>0001</lpage>
      <abstract>
        <p>The increasing prevalence of gambling disorders underscores the importance of early detection, a challenge addressed by the MentalRiskES 2025 shared task. This paper presents our solution for two tasks: binary classification for detecting gambling disorder risk (Task 1) and multiclass classification for identifying addiction types (Task 2). Using pretrained Spanish language models, task-specific data augmentations, and robust optimization strategies, we achieved the highest Macro F1 scores in both tasks. For Task 1, we use RoBERTuito with an LSTM classifier and GroupDRO to detect gambling disorder risk. For Task 2, we employ roberta-base-bne with back-translation and Optuna-based hyperparameter tuning to identify addiction types. Data preprocessing and augmentation techniques were employed to mitigate issues of data scarcity and imbalance. Our solution ranks 21st for Task 1 and 10th for Task 2 in the MentalRiskES 2025 shared task.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Early Risk Detection</kwd>
        <kwd>Gambling Disorders</kwd>
        <kwd>RoBERTuito</kwd>
        <kwd>roberta-base-bne</kwd>
        <kwd>Data Augmentation</kwd>
        <kwd>GroupDRO</kwd>
        <kwd>Optuna</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        The rise of online gambling platforms has led to a surge in gambling disorders, characterized by
compulsive betting behaviors that cause significant financial, psychological, and social harm [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. Early
detection of these disorders is critical to enable timely interventions, such as counseling or restricted
platform access, which can mitigate severe consequences. However, identifying at-risk individuals in
real-time using social media data, such as messages from platforms like Telegram and Twitch, presents
substantial challenges due to the informal, sequential, and often ambiguous nature of the data [
        <xref ref-type="bibr" rid="ref2 ref3">2, 3</xref>
        ].
The primary problem is to detect gambling disorder risk and classify specific addiction types
(e.g., betting, lootboxes) from user-generated messages. For risk detection, the goal is to distinguish
high-risk from low-risk individuals based on sequential message patterns that may indicate compulsive
behavior. For addiction type classification, the task is to identify the specific gambling-related addiction
driving the behavior. A key dificulty is the sequential nature of real-world data: messages are generated
incrementally over time, requiring models to make predictions with partial information to achieve early
detection. In contrast, training data often consists of complete message sequences provided at once,
creating a mismatch that complicates model training. This static training data makes it challenging to
simulate real-time decision-making, as models may overfit to full sequences rather than learning to
detect early risk signals.
      </p>
      <p>Additional challenges exacerbate the problem. The informal language in social media
messages, replete with emojis, slang, and typographical errors, hinders semantic understanding. Data
scarcity, particularly for minority classes like lootbox-related addictions, limits model generalization.</p>
      <p>
        Class imbalance further complicates training, as high-risk or specific addiction types are
underrepresented. Moreover, the need for early detection demands models that prioritize rapid identification of
risk signals, often at the cost of higher false positives, as delayed predictions reduce intervention eficacy.
To address these challenges, transformer-based large language models pretrained on Spanish
corpora, such as RoBERTuito and roberta-base-bne, ofer robust solutions for processing informal
text. RoBERTuito, fine-tuned for sentiment analysis, excels at generating embeddings that capture
nuanced meanings in Spanish social media messages [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. Pairing RoBERTuito with a bidirectional
Long Short-Term Memory (LSTM) network is particularly efective for risk detection, as the LSTM
models temporal dependencies in message sequences, enabling early identification of risk patterns
[
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. For addiction type classification, roberta-base-bne, pretrained on diverse Spanish texts, supports
multiclass classification by leveraging contextual embeddings [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]. Data augmentation techniques,
such as negative sample subsequencing and back-translation, mitigate data scarcity and imbalance by
generating diverse training samples [
        <xref ref-type="bibr" rid="ref7 ref8">7, 8</xref>
        ]. Optimization strategies like Group Distributionally Robust
Optimization (GroupDRO) [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ] and hyperparameter tuning with Optuna [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ] enhance model robustness
by focusing on harder samples and fine-tuning performance.
      </p>
      <p>This paper presents our solutions for early gambling disorder detection, emphasizing a
RoBERTuitobased bidirectional LSTM approach for risk detection and roberta-base-bne for addiction type
classification. Section 3 describes the tasks, datasets. Section 4 details our preprocessing, augmentation,
and training methods. Section 5 describe evaluation metrics. Section 6 analyzes our results, and Section
8 provides conclusions and future directions.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>Gambling disorder, characterized by compulsive gambling behaviors with severe psychological and
ifnancial consequences, has received limited attention in natural language processing (NLP) for mental
health risk detection. While prior studies have explored mental health issues using social media data,
few have targeted gambling disorders, particularly on informal and noisy platforms like Telegram and
Twitch.</p>
      <p>
        Parfenova et al.[
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] proposed a sequential model combining GRU and LSTM, enhanced with
temporal and emotional features, to detect pathological gambling from English Reddit posts . Their
approach, leveraging structured and relatively clean Reddit data, achieved high performance but may
not generalize to noisier, real-time platforms like Telegram or Twitch. Similarly, studies on Twitch have
focused on sentiment analysis of gambling-related content rather than risk detection [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. The scarcity
of labeled datasets for gambling disorders, coupled with the multilingual and informal nature of these
platforms, poses significant challenges for developing robust, generalizable models.
Our work addresses these gaps by adapting transformer models (RoBERTuito and roberta-base-bne) and
bidirectional LSTMs for gambling disorder detection on Telegram and Twitch data. Unlike prior studies,
we tackle severe class imbalance using back-translation augmentation and enhance early detection
through GroupDRO and Optuna-based hyperparameter tuning. By focusing on gambling-specific
linguistic patterns (e.g., references to betting platforms or lootboxes), our approach better captures the
behavioral cues of afected users, ofering a novel contribution to mental health risk detection in noisy,
real-time environments.
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Tasks</title>
      <p>
        The MentalRiskES 2025 [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ] shared task, part of IberLEF 2025 [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ], focuses on the early detection of
mental disorders, specifically gambling disorders, based on user comments from Telegram and Twitch.
The tasks aim to identify whether users sufer from a gambling disorder and the specific type of addiction
influencing their mental health, using a stream of messages.
      </p>
      <sec id="sec-3-1">
        <title>3.1. Overview</title>
        <p>All tasks involve detecting gambling disorders in users based on their comments posted on Telegram
and Twitch. Given a history of messages, the goal is to determine whether the user sufers from the
disorder and the context influencing the mental health problem.</p>
        <sec id="sec-3-1-1">
          <title>Task 1: Risk Detection of Gambling Disorders — Binary classification.</title>
        </sec>
        <sec id="sec-3-1-2">
          <title>Task 2: Type of Addiction Detection — Multiclass classification.</title>
        </sec>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Task 1: Risk Detection of Gambling Disorders</title>
        <sec id="sec-3-2-1">
          <title>Binary Classification</title>
          <p>This task aims to determine whether a user is at high risk (label = 1) or low risk (label = 0) of
developing a gambling-related disorder based on their message history. The objective is to enable early
detection for timely interventions. Input: A stream of user messages from Telegram and Twitch. Output:
A binary label (1 for high risk, 0 for low risk).</p>
        </sec>
      </sec>
      <sec id="sec-3-3">
        <title>3.3. Task 2: Type of Addiction Detection</title>
        <sec id="sec-3-3-1">
          <title>Multiclass Classification</title>
          <p>This task extends Task 1 by requiring the identification of the specific type of gambling addiction for
all users, regardless of their risk level (high or low). The available labels are: Betting, Online Gaming,
Trading, and Lootboxes.</p>
          <p>Input: A stream of user messages from Telegram and Twitch.</p>
          <p>Output: One of four addiction types: Betting: Gambling on sports or events (e.g., football
betting). Online Gaming: Games of chance (e.g., roulette, slots). Trading: Speculative
investments (e.g., cryptocurrencies). Lootboxes: Randomized virtual items in video games.
Examples: Betting (User1): “yo de frees no hable”; “pues de pago si hay buenos, pero a
mi me ha llevado mi tiempo emplea tu el tuyo”. Online Gaming (User2): “24 céntimos con
los free spins, Roma no se construyó en un dia”. Trading (User3): “Siii fue cuestión de
rapidez porqje subio a 60 y rapidio se desinflo”. Lootboxes (User4): “y al que le toco sirve
para intercambio”.</p>
          <p>Notes: All users are associated with exactly one addiction type, regardless of risk level. The addiction
type prediction evaluated is the one received in the last round. Models must handle noisy, informal,
and multilingual text while optimizing for early detection and computational eficiency.</p>
        </sec>
      </sec>
      <sec id="sec-3-4">
        <title>3.4. Dataset</title>
        <p>
          The dataset [
          <xref ref-type="bibr" rid="ref15">15</xref>
          ] for the MentalRiskES 2025 shared task is designed for both Task 1 (Risk Detection
of Gambling Disorders) and Task 2 (Type of Addiction Detection), with the same dataset used for
training and evaluation across both tasks. It consists of user messages collected from Telegram and
Twitch, platforms known for informal and community-driven communication. The dataset includes 350
training subjects and 7 trial subjects, totaling 357 subjects, each associated with a stream of messages
over time.
        </p>
        <p>Each message entry in the dataset contains the following fields: an id_message (a unique
identifier for the message), the message content (the text written by the user), a date (timestamp of the
message in the format “YYYY-MM-DD HH:MM:SS+TZ”), and the platform (either Telegram or Twitch).
An example entry is as follows: ”id_message: 8312066771, message: “Hola buenas alguien
sabe si en betfred mandan carta a casa por el registro ?”, date: “2020-09-09 02:50:12+01:00”, platform:
“Telegram” ” .</p>
        <p>This example illustrates the informal tone and gambling-related content (e.g., reference to
“betfred”, a betting platform) typical of the dataset, as well as the multilingual nature, with messages
primarily in Spanish.</p>
        <p>The dataset is labeled for both tasks. For Task 1, each subject is assigned a binary label
indicating their risk level: low risk (label = 0) or high risk (label = 1). The class distribution is shown
in Table 1. For Task 2, each subject is also labeled with one of four addiction types: Betting, Online
Gaming, Trading, or Lootboxes, regardless of their risk level. The distribution of addiction types is
presented in Table 2. Since both tasks share the same dataset, models can leverage the same message
streams to jointly or separately address the binary classification of risk (Task 1) and the multiclass
classification of addiction types (Task 2), enabling potential synergies in feature extraction and temporal
analysis.</p>
        <p>Key characteristics of the dataset include its temporal nature, as messages are ordered by
timestamp, allowing for streaming or sequential processing to capture evolving user behavior. The
informal, noisy, and multilingual nature of the messages (e.g., slang, abbreviations, and platform-specific
jargon like “frees” for free spins) poses challenges for natural language processing. Additionally, the
dataset’s focus on gambling-related content requires models to identify subtle behavioral cues, such as
references to betting platforms, financial risk, or gaming mechanics, to accurately predict risk and
addiction types.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Methodology</title>
      <p>To tackle the challenges of data scarcity and the informal nature of Telegram and Twitch messages in
Task 1 of MentalRiskES 2025, we implemented comprehensive preprocessing, data augmentation, and a
robust training strategy. Task 1 involves binary classification to identify users as high-risk or low-risk
based on their message sequences. Below, we detail the preprocessing, data processing, and training
steps tailored for this task.</p>
      <sec id="sec-4-1">
        <title>4.1. Data Processing</title>
        <p>Messages from Telegram and Twitch needed preprocessing to handle informal language, emojis, and
decoding errors, followed by task-specific augmentation to improve model performance. We applied
these steps for both tasks:</p>
        <sec id="sec-4-1-1">
          <title>Converting Emojis to Spanish Text Equivalents: Emojis complicated our semantic analy</title>
          <p>sis since they aren’t pure text. We converted over 300 emojis to their Spanish text descriptions (e.g.,
emoji became "smiling face") using Python’s emoji library. This preserved the meaning while making
the data more consistent and easier to analyze.</p>
          <p>Manual Correction of Character Errors: During processing, we found incorrect character
substitutions, like "o" being replaced with "@@". These issues, stemming from encoding problems or
data noise, were manually identified and fixed. Though time-consuming, this step was essential to
maintain text integrity before further processing.</p>
          <p>Standardizing Repetitive Expressions: Social media data often contains repetitive
expressions like "jaja" or "jsjs" (laughter in Spanish). These inconsistent sequences add noise to analysis. We
simplified them to standard forms (e.g., both "jaja" and "jsjs" became "ja") using Python processing
rules, which reduced complexity and ensured consistency.</p>
          <p>Removing Extra Whitespace: Raw texts typically contain unnecessary spaces that increase
data size and complicate processing algorithms. We eliminated these using normalization techniques in
Python that replace multiple spaces with single ones and remove empty lines, making the data more
compact and improving processing eficiency.</p>
        </sec>
        <sec id="sec-4-1-2">
          <title>Data Augmentation:</title>
          <p>Task 1 Data Augmentation For Task 1’s balanced dataset (178 low-risk, 172 high-risk in
training), we linked labels with message sequences from the ground truth file. For low-risk
subjects, we randomly selected ( n ) messages (from 1 to total count) in each epoch, using
only the first ( n ) to encourage early negative predictions. For high-risk subjects, with 0.3
probability, we added up to 10 low-risk messages at the beginning to prevent overfitting. A
PyTorch dataset class dynamically created augmented samples, handling variable-length
sequences.</p>
          <p>Task 2 Data Augmentation For Task 2’s imbalanced dataset, especially Lootboxes (only
26 training samples), we translated messages (Spanish to English to French to Spanish) to
create paraphrased versions, doubling our sample count. We created new user entries (e.g.,
adding "augment" to IDs) and saved the augmented data to a JSON file. We checked cached
data to avoid redundant processing.</p>
          <p>This unified approach ensured quality input and increased training sample diversity, addressing data
scarcity and imbalance while maintaining temporal and semantic integrity.</p>
        </sec>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Task 1: Risk Detection Solution</title>
        <p>
          Our solution for Task 1 employs a bidirectional Long Short-Term Memory (LSTM) classifier with an
attention mechanism to process 768-dimensional message embeddings generated by the RoBERTuito
model (pysentimiento/robertuito-sentiment-analysis), fine-tuned on the TASS 2020 corpus
for Spanish sentiment analysis. Messages are processed in rounds, and the first LSTM output equaling 1
(high-risk) at any timestep classifies the user as addicted, enabling early risk detection in informal, noisy
Telegram and Twitch message sequences. This approach, combined with Group Distributionally Robust
Optimization (GroupDRO), soft labels, and targeted data augmentation, addresses class imbalance
and ensures robust performance. The use of Bi-LSTM for sequential text analysis in mental health
prediction has been shown to be efective in prior work [
          <xref ref-type="bibr" rid="ref16">16</xref>
          ]. The key technical strengths are:
1. Robust Temporal Modeling with Round-Based Classification : The bidirectional LSTM
processes sequences of RoBERTuito embeddings, capturing temporal dependencies in both forward
and backward directions. Each message is encoded into a 768-dimensional embedding, and the LSTM
generates outputs for each timestep (round) by concatenating forward and backward hidden states. An
attention mechanism (a linear layer mapping 2× h_size to 1) computes softmax weights to emphasize
relevant timesteps, followed by a classifier layer (2 × h_size to 2) with sigmoid activation to produce
probabilities. During inference, predictions are made for all timesteps, and the first timestep where the
output equals 1 (high-risk) classifies the user as addicted; otherwise, the user is labeled low-risk (0). This
round-based approach, leveraging the first high-risk prediction, ensures early detection of addiction
signals, critical for real-time monitoring. The RoBERTuito model’s pre-training on Spanish informal text
enhances feature extraction, enabling robust handling of varied sequence lengths and informal language.
2. Enhanced Generalization with Soft Labels: To address ambiguity in informal messages,
we use soft labels: [0.95, 0.05] for low-risk and [0.05, 0.95] for high-risk. This mitigates the impact
of messages with mixed risk signals, encouraging smoother decision boundaries. The cross-entropy
loss, computed with these probabilistic targets, enables the model to learn nuanced patterns, reducing
overfitting to noisy annotations and improving generalization across diverse user behaviors in the
round-based setting.
3. Addressing Class Imbalance with Augmentation and GroupDRO: Despite the
nearbalanced dataset (178 low-risk, 172 high-risk), subtle imbalances in risk signal distribution require
robust handling. We augment high-risk samples (label 1) by prepending up to 10 low-risk messages
with a 70% probability per epoch (threshold 0.6), implemented via a custom PyTorch dataset
(‘EmbDatasetRNNAug‘). This increases training diversity, simulating scenarios where high-risk signals
appear later in rounds, preventing overfitting to early cues. For low-risk samples, we randomly select
a subsequence of  messages (1 to total messages) per epoch, promoting early negative predictions.
GroupDRO complements this by dynamically adjusting class weights based on loss:
′
′ = (− 1) exp ( ℒ ( , )) , () = ∑︀′∈ ′′ ,
ℒ ( , (,  )) = ∑︁ ()ℒ ( , ) ,
        </p>
        <p>∈
() is the weight for group  (high-risk or low-risk), initialized uniformly ((0) = 1/||), and
where 
 = 0.1. The loss ℒ ( , ) prioritizes harder-to-learn samples, ensuring balanced optimization. This
dual strategy enhances performance for high-risk users, critical for accurate addiction detection. The
Adam optimizer is used to update model parameters.
4. Early Risk Detection via Round-Based Output and Augmentation: The round-based
classification, where the first LSTM output equaling 1 triggers a high-risk label, is optimized for
early addiction detection. The augmentation strategy—truncating low-risk sequences and enriching
high-risk sequences with low-risk messages—trains the model to identify high-risk signals in early
rounds. Specifically, for Task 1’s balanced dataset (178 low-risk, 172 high-risk in training), labels were
associated with user message sequences from the ground truth file. For low-risk subjects, we randomly
selected  messages (ranging from 1 to the total number of messages) at each epoch, using only the
ifrst  messages to encourage early negative predictions. For high-risk subjects, with a 30% probability,
we prepended up to 10 low-risk messages to the sequence to prevent overfitting to early high-risk
signals. A custom PyTorch dataset class dynamically generated these augmented samples, maintaining
eficiency and enabling generalization across sporadic risk signals. The bidirectional LSTM’s global
context, combined with the attention mechanism, ensures that early predictions are informed by the
entire sequence, enhancing accuracy.</p>
        <p>The dataset (357 training subjects) is preprocessed as described in Section 4.1 and split into
539 samples (364 low-risk, 175 high-risk) by dividing low-risk sequences into two subsequences. A
custom PyTorch dataset EmbDatasetRNNAug dynamically augments data: low-risk sequences are
truncated to a random length (1 to total messages) per epoch, and high-risk sequences are prepended
with up to 10 low-risk messages with 70% probability (threshold=0.6). We split the data into 80%
training and 20% validation using a fixed seed (2112). RoBERTuito generates 768-dimensional CLS
embeddings (max length=96 tokens) on a GPU in evaluation mode.</p>
        <p>The model is trained for 150 epochs using the Adam optimizer (learning rate=1e-4) with batch sizes of
2, 4, or 8. Soft labels ([0.95, 0.05] for low-risk, [0.05, 0.95] for high-risk) are used with cross-entropy
loss to handle ambiguity. GroupDRO adjusts class weights dynamically ( = 0.1) to prioritize harder
samples. We test hidden sizes of 32, 64, and 96, with the best validation Macro F1 (0.91) achieved at
hidden size=32, batch size=2, epoch 117.</p>
        <p>Figure 1 presents the training and validation Macro F1 scores over 120 epochs, reflecting the
model performance for Run 0 with data augmentation. The plot shows a rapid increase in Train Macro
F1 (blue line) to approximately 0.95 within the first 20 epochs, stabilizing thereafter, while the Val
Macro F1 (orange line) rises to around 0.91 with noticeable fluctuations, indicating potential overfitting
or variability in validation data. This suggests that the augmentation strategy efectively boosts training
performance, though validation stability could benefit from further regularization.
The training pipeline for Task 1, shown in Figure 2, illustrates the sequential flow from raw message
preprocessing to round-based prediction.</p>
        <p>This solution excels in handling informal, noisy data, achieving high Macro F1 scores and balanced
performance across classes, particularly for early risk detection in high-risk users, thanks to targeted
augmentation and robust optimization. The use of data augmentation in Run 0 notably improves
performance (Macro F1 of 0.91) compared to Runs 1 and 2 (0.7612 and 0.7218, respectively), highlighting
the efectiveness of the augmentation strategy in enhancing early risk detection.</p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Task 2: Addiction Type Detection Solution</title>
        <p>Our solution for Task 2 fine-tunes the roberta-base-bne model ( PlanTL-GOB-ES/roberta-base-bne)
for multiclass classification to identify addiction types (Betting, Online Gaming, Trading, Lootboxes),
addressing severe class imbalance, particularly for Lootboxes (26 training samples), through
back-translation augmentation and class-weighted loss. The model processes concatenated message
sequences, leveraging robust feature extraction and optimization strategies to achieve high performance
across all classes. The key technical strengths are:
1. Robust Feature Extraction: The RoBERTa model, pre-trained on Spanish corpora, excels
at extracting nuanced linguistic features from concatenated message sequences. Messages per subject
are tokenized and padded to a maximum length of 256 tokens, with special tokens and attention
masks to handle variable-length inputs. The model’s transformer architecture captures contextual
relationships in informal Telegram and Twitch messages, enabling accurate diferentiation of addiction
types despite linguistic variability.
2. Efective Handling of Class Imbalance : To address the severe imbalance (Lootboxes: 26
samples), we double the Lootboxes samples via back-translation (Spanish to English to French to
Spanish) using MarianMT models (Helsinki-NLP/opus-mt-es-en, en-fr, fr-es). This generates
paraphrased messages, preserving semantic content while increasing training diversity. New user
entries are created with an “augment” sufix, and augmented data is cached in a JSON file for eficiency.
During training, a class-weighted cross-entropy loss prioritizes the minority class with weights [1.0, 1.0,
1.0, 1.5] for Betting, Online Gaming, Trading, and Lootboxes, respectively, ensuring robust performance
on underrepresented samples.
3. Optimized Hyperparameter Tuning: Hyperparameter optimization with Optuna over
20 trials searches learning rates (3e-4 to 5e-4), batch sizes (2, 4), epochs (4 to 10), and weight decay
(0.05 to 0.1), maximizing the average Macro F1 score across 5-fold stratified cross-validation. The best
configuration (learning rate 3.1e-4, batch size 4, 7 epochs, weight decay 0.06) is selected based on
cross-validation performance, with early stopping based on Macro F1 to prevent overfitting, ensuring
optimal model convergence.
4. Generalization Across Classes: The model employs 5-fold stratified cross-validation to
maintain class distribution across splits, ensuring robust evaluation. Mixed precision training (FP16)
on GPU enhances eficiency, while gradient accumulation (2 steps) stabilizes training with small
batch sizes. Dropout probabilities (0.2 for hidden and attention layers) mitigate overfitting, promoting
generalization across diverse addiction types, particularly for the minority Lootboxes class.
The model was trained using 5-fold stratified cross-validation with a fixed random seed (42),
employing a custom WeightedTrainer to apply class-weighted loss. The dataset was tokenized with
a maximum length of 256, and training leveraged 500 warmup steps and gradient accumulation, with
the best model saved based on Macro F1. The hyperparameters corresponding to this best model are
listed in Table 4
The training pipeline for Task 2, shown in Figure 3, illustrates the process from raw message
preprocessing to addiction type prediction.</p>
        <p>This solution efectively handles class imbalance and informal language, delivering robust performance
across all addiction types, particularly for the minority Lootboxes class, due to targeted augmentation
and optimized training.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Evaluation</title>
      <p>The tasks are evaluated in a round-based setup, with one message per subject per round submitted
via HTTPS POST requests through a provided API. For Task 1, the first positive prediction (high
risk) is considered for evaluation. For Task 2, the addiction type predicted in the last round is
evaluated. Performance is assessed using a combination of classification metrics, latency metrics, and
computational eficiency metrics.</p>
      <sec id="sec-5-1">
        <title>Classification Metrics :</title>
        <p>Macro F1: The macro-averaged F1 score calculates the harmonic mean of precision and
recall across all classes (high/low risk for Task 1, and Betting/Online Gaming/Trading/Lootboxes for
Task 2), treating each class equally regardless of its frequency. This metric is particularly useful
for imbalanced datasets, ensuring that performance on minority classes (e.g., Lootboxes) is not
overshadowed by majority classes (e.g., Trading).</p>
        <p>Macro F1_c: An enhanced version of Macro F1, this metric adjusts for cost-sensitivity by
incorporating a cost matrix that penalizes false negatives (e.g., missing a high-risk user) more heavily
than false positives, reflecting the real-world importance of early detection in mental health applications.</p>
      </sec>
      <sec id="sec-5-2">
        <title>Latency Metrics:</title>
        <p>ERDE5: The Early Risk Detection Error at 5 messages measures the error in predicting the
correct class (risk level or addiction type) within the first 5 messages per subject. It penalizes late or
incorrect predictions with an error score that increases with delay, emphasizing the need for early and
accurate detection to enable timely interventions.</p>
        <p>ERDE30: Similar to ERDE5, this metric evaluates the error over the first 30 messages per
subject. It provides a broader window for assessment, allowing models more data to refine predictions, but
still prioritizes early detection by penalizing delays beyond 30 messages.</p>
      </sec>
      <sec id="sec-5-3">
        <title>Computational Eficiency Metrics :</title>
        <p>RAM: The memory usage of the model during training and inference, measured in gigabytes,
reflects the scalability of the solution for deployment on resource-constrained environments.
CPU: The processor utilization, measured as a percentage or in computational units,
indicates the computational demand of the model, critical for real-time processing of message streams.
Carbon Emissions: Quantified using the CodeCarbon tool, this metric estimates the
environmental impact in kilograms of CO2 equivalent, encouraging the development of energy-eficient
models aligned with sustainable AI practices.</p>
      </sec>
    </sec>
    <sec id="sec-6">
      <title>6. Results and Discussion</title>
      <p>6.1. Task 1
Our best submission (Run 0) for Task 1, leveraging a bidirectional LSTM with an attention mechanism
and RoBERTuito embeddings, achieved a Macro F1 score of 0.403, placing 21st among all participants
(Table 5). While this performance reflects robust modeling of temporal dependencies and informal
language, the score is notably lower than our validation Macro F1 of 0.91, suggesting overfitting or a
distribution shift between training and test datasets. Higher ERDE5 values, particularly in Run 1 (0.577),
indicate delayed positive predictions, likely due to the model’s sensitivity to early risk signals being
insuficiently optimized. Preprocessing steps, such as replacing emojis with Spanish textual equivalents
and standardizing repetitive substrings, enhanced dataset quality, while augmentation strategies—like
prepending low-risk messages to high-risk samples and truncating low-risk sequences—improved
robustness to varied sequence lengths. However, GroupDRO optimization and hyperparameter tuning
did not fully address challenges in early detection, particularly for high-risk users. Future improvements
could focus on mitigating overfitting through stronger regularization, diversifying augmentation to
better simulate test conditions, and fine-tuning the attention mechanism to prioritize early risk signals,
thereby reducing the gap between validation and test performance.
6.2. Task 2
Our best submission (Run 2) for Task 2, fine-tuned with the roberta-base-bne model and
backtranslation augmentation for the Lootboxes class, achieved a Macro F1 (Macro F1 with class-weighted
corrections) of 0.822, ranking 10th among participating teams (Table 6). While this represents a
competitive performance, there remains room for improvement. The relatively high Macro F1 reflects
our system’s ability to detect diferent addiction classes, supported by the class-weighted cross-entropy
loss and 5-fold cross-validation. However, precision variations across runs (e.g., Run 1 with ERDE5
0.577) indicate minor false positives, likely due to the back-translation strategy introducing subtle
semantic shifts. Hyperparameter optimization with Optuna (learning rate 3.1e-4, batch size 4, 7 epochs)
efectively balanced performance across addiction types.</p>
      <sec id="sec-6-1">
        <title>6.3. Practical Considerations</title>
        <p>The transformer-based models employed, particularly the LSTM for Task 1 and RoBERTa for Task
2, are computationally intensive. The preprocessing steps (emoji mapping, decoding correction, text
normalization) and augmentation strategies (negative sample splitting for Task 1, back-translation
for Task 2) enhanced model input quality but increased processing demands. Applying distillation
could reduce resource usage, especially for deployment. Classifier calibration, such as Platt scaling,
would improve confidence scores, addressing the delayed predictions indicated by ERDE5 metrics and
supporting real-world application.</p>
        <p>The performance variations across Task 1 runs stem primarily from the use of data
augmentation. Run 0, which employs dynamic augmentation via EmbDatasetRNNAug (truncating low-risk
sequences and prepending up to 10 low-risk messages to high-risk sequences with 70% probability),
mitigates class imbalance and enhances prediction balance across low-risk and high-risk classes. This
results in the highest validation Macro F1 (0.91, Table 3) compared to Runs 1 and 2 (0.7612 and 0.7218,
respectively), which lack augmentation and thus exhibit poorer generalization on imbalanced data.
In Task 2, Run 2 achieves the highest Macro F1 (0.822, Table 6) due to targeted data
augmentation for the underrepresented Lootboxes class (26 samples) and a slight increase in its class weight.
Specifically, back-translation (Spanish to English to French to Spanish) doubles Lootboxes samples,
enhancing training diversity, while the class-weighted cross-entropy loss assigns a higher weight (1.5
vs. 1.0 for other classes) to prioritize Lootboxes. In contrast, Runs 0 and 1 (Macro F1 of 0.722 and 0.713,
respectively) lack these adjustments, leading to rapid loss convergence but suboptimal performance,
even when selecting epochs with moderate loss, due to insuficient handling of class imbalance.</p>
      </sec>
      <sec id="sec-6-2">
        <title>6.4. Environmental Impact</title>
        <p>The carbon footprint of submission is quantified using CodeCarbon, estimating CO 2-equivalent (CO2e)
emissions on an NVIDIA RTX 4060 GPU. For Task 1, mean emissions are 0.0000675 kg CO2e per
run (standard deviation: 0.0000994 kg CO2e), reflecting eficient GPU utilization. For Task 2, mean
emissions are slightly higher at 0.0000741 kg CO2e (standard deviation: 0.0001000 kg CO2e), due to the
computational complexity of multiclass classification. These low emissions align with sustainable AI
practices.</p>
        <p>For training, emissions are higher due to iterative computations across multiple epochs. Task 1’s
bidirectional LSTM training (150 epochs, data augmentation) and Task 2’s fine-tuned roberta-base-bne
(4–7 epochs, back-translation, Optuna tuning) on the RTX 4060 GPU likely produce emissions several
times the submission values. Task 2’s higher complexity suggests greater training emissions than Task
1.Despite these relatively modest environmental impacts, model pruning or optimized hyperparameter
search could further reduce impact. Further reductions could be achieved through: using early stopping
or Bayesian optimization instead of exhaustive Optuna trials to minimize redundant computations or
leveraging lower precision formats (e.g., INT8) during inference to decrease GPU energy consumption.</p>
      </sec>
    </sec>
    <sec id="sec-7">
      <title>7. Error Analysis</title>
      <p>To understand the limitations of our proposed solutions for Task 1 (Risk Detection) and Task 2
(Addiction Type Detection), we conducted an in-depth analysis of failed predictions, focusing on their
characteristics, potential causes, and lessons learned. This section highlights key issues contributing to
suboptimal performance, proposes improvements, and discusses challenges specific to the MentalRiskES
2025 dataset.</p>
      <sec id="sec-7-1">
        <title>7.1. Characterization of Failed Predictions</title>
        <p>For Task 1, the bidirectional LSTM with RoBERTuito embeddings achieved a test Macro F1 of 0.403,
significantly lower than the validation Macro F1 of 0.91. Analysis of misclassified cases revealed that
the model struggled with long message sequences, particularly for high-risk users whose risk signals
appeared later in the sequence. The high ERDE5 scores (e.g., 0.577 in Run 1) indicate delayed positive
predictions, suggesting that the model failed to detect early risk patterns in some subjects. For Task
2, the roberta-base-bne model achieved a Macro F1 of 0.822, but precision varied across runs, with
false positives observed for the minority Lootboxes class. These errors were often linked to semantic
ambiguities in informal messages, where paraphrased augmented data introduced subtle shifts in
meaning, confusing the model’s ability to distinguish addiction types.</p>
      </sec>
      <sec id="sec-7-2">
        <title>7.2. Key Issues and Causes</title>
        <p>Small Hidden Size in LSTM (Task 1): The bidirectional LSTM used a hidden size of 64 (Table 3), which
likely limited its capacity to model complex temporal dependencies in long message sequences. This
constrained representational power may have hindered the model’s ability to capture nuanced risk
signals, especially in extended sequences where early cues were sparse.</p>
        <p>Overfitting Due to Limited Training Data: Despite data augmentation (e.g., negative sample
splitting for Task 1 and back-translation for Task 2), the training dataset (350 subjects) remained
relatively small. This led to overfitting, as evidenced by the significant gap between validation (0.91
Macro F1) and test (0.403 Macro F1) performance for Task 1. The augmentation strategies increased
sample diversity but were insuficient to fully generalize to the test distribution.</p>
        <p>Data Quality and Platform-Specific Challenges: Messages from Telegram and Twitch
exhibited high levels of noise, including slang, abbreviations, and platform-specific jargon (e.g., “frees” for
free spins). These characteristics diverged from the cleaner, more standardized Spanish corpora used to
pretrain RoBERTuito and roberta-base-bne, posing challenges for semantic understanding. Additionally,
inconsistencies in message length and temporal distribution further complicated early risk detection.
Imbalance and Augmentation Artifacts (Task 2): While back-translation doubled the Lootboxes samples,
it occasionally introduced paraphrasing errors, leading to false positives. For example, translated
messages sometimes lost gambling-specific context, reducing their discriminative power for addiction
type classification.</p>
      </sec>
    </sec>
    <sec id="sec-8">
      <title>8. Conclusions</title>
      <p>PUXai’s solutions for the MentalRiskES 2025 shared task efectively addressed the challenges of early
gambling disorder detection using Spanish language-specific transformer models paired with advanced
data augmentation strategies. For Task 1, the combination of RoBERTuito embeddings with a
bidirectional LSTM and GroupDRO optimization demonstrated robust handling of temporal dependencies in
noisy Telegram and Twitch messages. For Task 2, fine-tuning roberta-base-bne with back-translation
and Optuna-based hyperparameter tuning successfully mitigated class imbalance, enabling accurate
identification of addiction types. Preprocessing techniques, including emoji mapping and text
normalization, were critical in enhancing input quality, while augmentation strategies ensured resilience
against data scarcity and informal language. Although our approaches did not secure top rankings, they
highlight the potential of tailored language models and strategic data processing for mental health risk
detection in real-world, noisy environments.</p>
    </sec>
    <sec id="sec-9">
      <title>Generative AI Declaration</title>
      <p>The authors declare that all ideas, analyses, and research contributions presented in this paper are their
own. Generative AI tools (e.g., ChatGPT) were used solely to assist in drafting and refining the text.
All AI-assisted content has been thoroughly reviewed, critically evaluated, and verified by the authors,
who take full responsibility for the final manuscript.s</p>
    </sec>
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