<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.0 20120330//EN" "JATS-archivearticle1.dtd">
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  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>Microposts</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>Leveraging Blogging Activity on Tumblr to Infer Demographics and Interests of Users for Advertising Purposes</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Mihajlo Grbovic</string-name>
          <email>mihajlo@yahoo-inc.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vladan Radosavljevic</string-name>
          <email>vladan@yahoo-inc.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Nemanja Djuric Narayan Bhamidipati</string-name>
          <email>nemanja@yahoo-inc.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ananth Nagarajan</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Yahoo Labs 701 First Ave</institution>
          ,
          <addr-line>Sunnyvale, CA</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2016</year>
      </pub-date>
      <volume>6</volume>
      <fpage>2</fpage>
      <lpage>11</lpage>
      <abstract>
        <p>As one of the leading platforms for creative content, Tumblr offers advertisers a unique way of creating brand identity. Advertisers can tell their story through images, animation, text, music, video and more, and they can promote that content by sponsoring it to appear as an advertisement in the streams of Tumblr users. In this paper, we present a framework that enabled one of the key targeted advertising components for Tumblr, specifically, gender and interest targeting. We describe the main challenges involved in the development of the framework, which include the creation of a ground truth for training gender prediction models, as well as mapping Tumblr content to an interest taxonomy. For purposes of inferring user interests, we propose a novel semi-supervised neural language model for categorization of Tumblr content (i.e., post tags and post keywords). The model was trained on a large-scale data set consisting of 6.8 billion user posts, with a very limited amount of categorized</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>Categories and Subject Descriptors</title>
      <p>H.2.8 [Database applications]: Data Mining
data mining; computational advertising; audience modeling;
algorithms
Permission to make digital or hard copies of all or part of this work for personal or
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      <p>K#DMD’i1c5ro,Apougsutst21001-61,3,A2p01r51,S1ythdn,e2y,0N16S,WM,Aounstrraélaial., Canada.
c 2015 ACM. ISBN 978-1-4503-3664-2/15/08 ...$15.00.</p>
      <p>DOI: http://dx.doi.org/10.1145/2766XXX.XXXXXXX.</p>
    </sec>
    <sec id="sec-2">
      <title>1. INTRODUCTION</title>
      <p>
        In recent years, online social networks have evolved to
become an important part of life for online users of all
demographic and socio-economic backgrounds. They allow users
to easily stay in touch with their friends and family, discuss
everyday events, or share their interests with other users
with the click of a button. Tumblr is one such social
network, representing one of the most popular and fastest
growing networks on the web. Hundreds of millions of people
around the world come every month to Tumblr to find,
follow, and share what they love. The Tumblr network is a gold
mine of content, comprising of 200 million blogs on different
topics such as travel, sports, and music, where 85 million
user posts are published on a daily basis. This wealth of
user-generated data opens a great opportunity for
advertisers, allowing them to promote their products through
highquality targeting campaigns to both blog visitors and blog
owners [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ].
      </p>
      <p>
        The standard, prevalent form of advertising on Tumblr is
through sponsored posts that appear alongside regular posts
in the user’s dashboard, the central page for a Tumblr user,
displaying the newest posts of followed blogs in the form
of a stream. This form of advertising, in which
advertisements resemble native content in the stream, is often referred
to as native advertising. Native advertisements are usually
aesthetically beautiful and highly engaging, which typically
makes them more enjoyable than regular display ads [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
Tumblr launched its native advertising product in May of
2012. Since then, the number of advertisers (or brands) on
the platform has grown steadily and reached a milestone
of 100 advertisers in April of 2013. Moreover, most of the
biggest global brands have used Tumblr to advertise and
sponsored posts have generated billions of paid ad
impressions since the launch of the Tumblr advertising product1.
In this paper, we further enhance ad targeting that Tumblr
offers, allowing advertisers to specify new demographic or
interest categories. This improved targeting provides
advertisers with the control and flexibility to find the audience
they most want to reach.
      </p>
      <p>
        Building of interest targeting products on social and
microblogging platforms is an important research topic,
discussed previously by several researchers [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. However, due
to its distinct characteristics, Tumblr poses novel challenges,
      </p>
      <sec id="sec-2-1">
        <title>1www.comscore.com, accessed June 2015</title>
        <p>which we explain in detail in this paper. In particular, the
content and language used on Tumblr have distinct
characteristics that needed to be accounted for during the
modeling. Users often use tags to summarize the text in their
posts. However, the language styles used in the tags and
post text are different (e.g., the tag “hp” and the word
“hp” have different meanings when they appear in the posts,
“Harry Potter” and “HP company”, respectively).
Moreover, unlike the popular social platform Facebook, which
contains a large amount of social interactions but a limited
amount of content, or the microblogging platform Twitter,
which contains an intermediate amount of social
interaction and content, Tumblr represents a unique combination
of a rich and diverse content platform and a dynamic
social network. To make use of this vast advertising potential,
we propose to classify user-generated Tumblr content into a
standard multi-level general-interest taxonomy 2 that
advertisers commonly use for defining their targeting campaigns,
opening doors to high-quality audience segmentation and
modeling for purposes of ad targeting. However, inferring
categories of user posts is a challenging task, given the huge
quantities of unlabeled data being posted every day and the
very limited amount of labeled data, typically obtained by
human editorial efforts. To this end, we propose a novel
semi-supervised neural language model, capable of jointly
learning embeddings of post keywords, post tags and
category representations in the same feature space. The neural
model was trained on a large-scale data set comprising of
6.8 billion posts, with only a fraction of categorized content.</p>
        <p>Targeting pipelines described in this paper are being used
to show ads to millions of users daily, and have substantially
improved Tumblr’s business metrics following the launch.
On our path to developing targeting capabilities for
Tumblr, we first created user profiles, based on users’ Tumblr
activities that include publishing blog posts, following other
blogs, liking posts, and other. Lastly, we aimed at
building and delivering both demographic and interest predictive
models based on the created profiles.</p>
        <p>We note that the privacy of our users is of critical
importance. Therefore, we were constrained in regards to what
data we can use. Specifically, user profiles were created
solely from data which users share publicly with others,
including contents of blog posts, blog titles and descriptions,
and follow, like and reblog actions. This data is publicly
available through Tumblr Firehose data source3. Other user
activities, such as user searches on Tumblr, which blogs they
visited and where they clicked, are considered to be sensitive
data and were not used in any way for the development of
the ad targeting models.
2.</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>RELATED WORK</title>
      <p>
        Personalization is defined as “the ability to proactively
tailor products and product purchasing experiences to tastes of
individual consumers based upon their personal and
preference information” [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ], and it has become an important topic
in recent years. Personalization of online content for
individual users may lead to improved user experience and directly
translate into financial gains for online businesses [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ]. In
addition, personalization fosters a stronger bond between
customers and companies, and can help in increasing user
loyalty and retention [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. For these reasons it has been
recognized as a strategic goal and is the focus of significant
research efforts of major internet companies [
        <xref ref-type="bibr" rid="ref12 ref8">8, 12</xref>
        ].
      </p>
      <p>
        We consider personalization through the domain of ad
targeting [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], where the task is to find the best matching ads
to be displayed for each individual user. This improves the
user’s online experience (as only relevant and interesting ads
are shown) and can lead to increased revenue for the
advertisers (as users are more likely to click on the ad and make a
purchase). Due to its large impact and many open research
questions, targeted advertising has garnered significant
interest from the machine learning community, as witnessed
by a large number of recent workshops4. and publications
[
        <xref ref-type="bibr" rid="ref11 ref5">5, 11</xref>
        ].
      </p>
      <p>
        One of the basic approaches in ad targeting is to target
users with ads based on their demographics, such as age or
gender. Historically, this approach has proven to work better
than targeting random users. However, while for some
products this type of targeting may be sufficient (e.g., women’s
makeup, women’s clothing, man’s razors, man’s clothing),
for others it is not effective enough and a more involved
profiling of users is required. A popular method in today’s
ad targeting that addresses this issue is known as interest
targeting, in which users are assigned interest categories,
such as “sports” or “travel”, based on their historical
behavior [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. Typically, a taxonomy is used to decide on the
2http://www.iab.net/QAGInitiative/overview/
taxonomy
      </p>
      <sec id="sec-3-1">
        <title>3gnip.com/sources/tumblr 4www.targetad-workshop.net</title>
        <p>
          targeting categories, and a model is learned to categorize
user activities and estimate their interest in each category.
Interest targeting is known to build good brand awareness
with relevant audience, which has already shown interest in
the corresponding category. In this paper we follow this
interest targeting approach. Alternatively, advertisers may be
interested going a step forward and optimizing for intent,
typically done by assigning categories to actual ads, and
training a machine learning model to estimate the
probability of an ad click in that category [
          <xref ref-type="bibr" rid="ref17">17</xref>
          ]. For each ad category
a separate predictive model is trained, and evaluated on the
entire user population, with N users with the highest score
selected for ad exposure.
        </p>
        <p>
          To the best of our knowledge, the Tumblr social network
has been considered by only a few scientific studies. In [
          <xref ref-type="bibr" rid="ref15 ref3">3,
15</xref>
          ], the authors discuss the problem of blog
recommendation, while in [
          <xref ref-type="bibr" rid="ref6">6</xref>
          ] they explore Tumblr social norms.
However, our work is the first paper that addresses ad targeting
on Tumblr.
        </p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>WHAT IS TUMBLR?</title>
      <p>Tumblr5 is one of the most popular social blogging
platforms, where users can create and share posts with the
followers of their blogs. According to data from January 20156,
there is a total of 221.6 million blogs on Tumblr, which
jointly produced over 102.7 billion blog posts. With a large
number of users signing up every day, Tumblr is currently
the fastest growing social platform7.
3.1</p>
    </sec>
    <sec id="sec-5">
      <title>User activities on Tumblr</title>
      <p>To register for a Tumblr account, a valid e-mail address is
required, along with a primary username (which will become
a part of the blog URL) and a confirmation of age. A Tumblr
blog resembles a webpage, with a profile picture, blog title
and blog description appearing at the top (see Figure 1),
followed by a stream of blog posts bellow. The first blog
5www.tumblr.com
6www.tumblr.com/about
7http://t.co/3txHFRJreJ
title
body
tags
reblog
like
created by a registered user is considered his or her primary
blog. In addition, a very small portion of users maintain
one or more secondary blogs. A Tumblr user is uniquely
described by the blog ID of the primary blog, and throughout
the paper we will use “blog” and “user” interchangeably.</p>
      <p>
        Common user activities of Tumblr users include the
following: 1) creating a post on one’s blog; 2) sharing a post
created by another blog, called reblogging (a reblogged post
will appear on the user’s blog); 3) liking a post by another
blog; and 4) following another blog. Similar to Twitter, the
follow connections at Tumblr are uni-directional. However,
unlike Twitter, users can create longer and richer content in
the form of several post types, such as text, photo, quote,
link, chat, audio and video. The most popular types of blog
posts are photo posts and text posts, and, based on the
analysis published in [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ], together they cover more than
92% of all posts on Tumblr (see Figure 2). Any post type
can be annotated with words starting with # that concisely
describe the post and allow for easier browsing and
searching (called tags). Additional metadata that describes a post
includes photo captions in photo posts, post titles in text
posts, and artists names in audio posts. An example post
is shown in Figure 3. Tags, such as #gadgets or #tech, are
displayed bellow the photo caption, while the buttons for
reblog and like actions are located in the bottom right corner.
Lastly, each user has a dashboard (i.e., a feed of blog posts
published by followed users, which is ordered in time), with
more recent posts appearing at the top.
3.2
      </p>
    </sec>
    <sec id="sec-6">
      <title>Advertising at Tumblr</title>
      <p>Advertising on Tumblr is implemented through the
mechanism of sponsored (or promoted) posts shown in a user’s
dashboard. This is similar to how advertising works on
Twitter and Facebook. A sponsored post can be a video, an
image, or simply a textual post containing an advertising
message. In Figure 4, we show an example of a sponsored post
and how it appears on web and mobile dashboards.
Similarly to organic (or non-promoted) posts, sponsored posts
can propagate from user to user in the network by means of
reblogs, and users can also “like” the promoted post. Both
likes and reblogs can be seen as an explicit form of
acceptance or endorsement of the advertising message. Moreover,
THAT ARE
FFECTIVE
images
by
video
rease the
just like any other posts, sponsored posts are supplemented
with notes on who liked and reblogged the post.</p>
      <p>Interestingly, while user-generated, organic posts are
reblogged on average 14 times, sponsored posts are reblogged
on average 10,000 times8. We have observed that 40% of
engagements with sponsored posts are reblogs, likes, or
follows. What is more, every fourth reblog of a sponsored
post results in 6 downstream reblogs from followers, leading
to content longevity, and one third of reblogs of sponsored
posts are present for 30 days or more after the initial post.</p>
    </sec>
    <sec id="sec-7">
      <title>TUMBLR DATA</title>
      <p>In this section, we describe the data sources (user
activities and post contents) utilized to create user profiles.
In particular, user activities included actions such as posts,
likes, follows and reblogs, while post contents included tags,
the title and body for text posts, artist names from audio
posts, as well as tags and captions for photo posts.
4.1</p>
    </sec>
    <sec id="sec-8">
      <title>Data sources</title>
      <p>Once signed in onto Tumblr, a user can follow other users’
blogs. The follow action is one-directional as it does not
require the follow back. For the purpose of this study, we
collected a sub-graph which contained 96.9 million unique
nodes (i.e., users), 5.1 billion edges (i.e., follows), out of
which 36.4 million are bi-directional (18.2 million pairs of
users that follow each other). The data set included more
than 26.1 billion activities on Tumblr. As discussed
earlier, an activity log is available through a data feed called
Firehose.</p>
      <p>To create user profiles for targeting, textual contents of all
posts were collected, including photo captions, tags, titles
and bodies. In addition, every time a user performs a post
or reblog activity, Firehose lists the user’s blog title and
blog description, which we also used to represent a user.
As we can see in Figure 1, a blog title and description often
provide useful information with respect to targeting, such as</p>
      <sec id="sec-8-1">
        <title>8http://yhoo.it/1vFfIAc</title>
        <p>In order to improve the representation of user profiles, we
propose to extract keywords from available blog
information. This requires a certain amount of data preparation
and processing. Given the extracted blog data, including
the title, content and tags, we first removed all the html
tags, followed by the removal of stopwords and the
formation of bigrams. It is common for certain words to appear
together more often than some others (e.g., words “credit”
and “card”), and we aim to capture those bigrams and use
them in keyword-based user profiles. To detect bigrams, we
use a procedure that counts the unigram and bigram
appearances, and for each combination of words wi and wj it
calculates the following score:
score(wi, wj ) =</p>
        <p>count(wi, wj )
count(wi)count(wj )
.</p>
        <p>(4.1)
Finally, bigrams with a score above a certain threshold were
extracted from the text in blog contents. Tags, on the other
hand, naturally form n-grams, and we extracted them in
their original form.
4.3</p>
      </sec>
    </sec>
    <sec id="sec-9">
      <title>User profiles</title>
      <p>Available data sources were used to create user profiles. In
particular, we extracted three distinct groups of user-related
data: 1) declared; 2) content of posts; and 3) actions. The
specific components included in each of the data groups are
listed in Table 1. From each group we extracted features to
represent the users as described below.</p>
      <p>Declared data consists of information which a user
provided during sign-up, including keywords from the blog title
and blog description, where keywords were extracted using
the method in Section 4.2. To create user profiles we kept
the most frequent keywords from blog titles and
descriptions, after removing stopwords such as “a”, “the”, “where”,
“in”. We counted the keyword frequency in a user’s blog title
and description, and stored the count along with the time
stamp of the latest log-in as a part of the user profile.</p>
      <p>Content features were formed from the textual contents
of posts which a user either created or reblogged. The main
content feature types included: 1) post tags; 2) keywords
from the post title and body; 3) keywords from photo post
captions; and 4) artist names from audio posts. Tags in
posts were not tokenized, instead they were used in the form
they appear, e.g., tag “food for a vegan” was one keyword.
On the other hand, in order to extract keywords from text
appearing in text post content, we again used the method
from Section 4.2. We kept only the most frequently
occurring keywords, excluding stopwords. In addition, we used
the most popular artist names as keywords. In this way,
we collected several millions of distinct keywords that were
tags  within  a  single  post  
tj-­‐n   …   tj-­‐1  
tj+1   …   tj+n  
tags  within  a  single  post  
tj-­‐n   …   tj-­‐1  
tj+1   …   tj+n  
Projec(on  </p>
      <p>tj  
j-­‐th  tag  
Projec/on  </p>
      <p>tj   c1   …   ck  
j-­‐th  tag   j-­‐th  tag  categories  
used to obtain rich representation of user profiles. To
illustrate content keyword extraction from our dataset,
consider that user ui at time stamp t used tag #hp five times
and tag #nba eight times, keyword football two times in
post titles and posted an audio post with a song from artist
Shakira ten times, then the resulting user profile would be:
ui = {tag : {#hp, t : 5, #nba, t : 8}, title : {f ootball, t :
2}, artist : {shakira, t : 10}}.</p>
      <p>Action features include follows, likes, and reblogs. If
user ui follows user uj at time stamp t, we create an
indicator feature f ollows : {j, t : 1} and add it to the ui’s user
profile. Similarly, if user ui likes or reblogs user uj’s post,
we create a feature that keeps record of the number of likes
m and reblogs n, as likes : {j, t : m}, reblogs : {j, t : n},
respectively, and update the user profile accordingly.</p>
      <p>The described approach resulted in user profiles for a total
of 81.8 million users. The total number of unique features
was 1.4 million, and an average user had 379.9 non-zero
features. Most of the features described above are represented
as either binary indicators or counts of occurrences.</p>
    </sec>
    <sec id="sec-10">
      <title>5. INTEREST PREDICTION</title>
      <p>
        The goal of our work is to infer user demographics
(described in the following section) and identify user groups
with interests in certain topics, such as music, travel,
cooking or books, in order to allow advertisers to target
segmented Tumblr audiences. As the topics may be defined at
various levels of granularity, to avoid sparsity problems while
still providing useful and actionable interest categories, user
interests are often classified into a pre-determined
hierarchical interest taxonomy that the advertisers commonly use.
However, to be able to create effective user interest
classifiers, one requires a sufficient amount of labeled data. Yet,
for the problem of the scale of Tumblr interest prediction,
this can be a daunting task for human editors. For that
reason we propose a novel semi-supervised classification
approach, based on the recently proposed word2vec model [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ],
which efficiently and seamlessly makes use of large amounts
of unlabeled and a limited amount of editorially labeled data
for learning effective content classifiers.
5.1
      </p>
    </sec>
    <sec id="sec-11">
      <title>User interest taxonomy</title>
      <p>We decided to classify keywords into the General
Interest Taxonomy (GIT), used by the Yahoo Gemini
advertising platform for native advertising9. The GIT is carefully
derived based on Interactive Advertising Bureau (IAB)
taxonomy recommendations, in order to meet advertiser needs
and protect Yahoo’s interests. The GIT has a two-level
hierarchical structure, such that advertisers can adjust the
audience reach by utilizing broader or narrower interest
categories. The top level of the taxonomy contains 23 nodes
(e.g., “Automotive”, “Business”, “Pets”, “Travel”), while the
second level contains 130 nodes which represent more precise
interests (e.g., “Automotive/SUV”, “Automotive/Luxury”,
“Pets/Dogs”).
5.2</p>
    </sec>
    <sec id="sec-12">
      <title>Proposed semi-supervised classification</title>
      <p>
        In this section, we present a novel classification approach
based on the recently proposed skip-gram model [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ], which
is used to categorize keywords into the GIT taxonomy. For
conciseness, we describe the proposed model on the
assumption that it is applied to tag categorization. However, we
used the same methodology for categorization of keywords
originating from blog titles, descriptions and text, audio and
image posts.
      </p>
      <p>We consider the task of tag classification, where the goal
is to classify tags into a pre-defined taxonomy of interest
categories. In order to address this problem, we propose
to learn tag representation in a low-dimensional space using
neural language models that are applied to historical
Tumblr posts. Let us assume that we are given N posts. In the
post logs found in Firehose, every post pi is recorded along
with the tags tij , j = 1...M . We collected data in the form
pi = {tij , j = 1...Mi}, where Mi represents the number of
N
tags in the i-th post. Given the data set D = ∪i=1pi, the
objective is to find a representation of tags in which
semantically similar tags are nearby in the representation space.
For this purpose, we extend ideas originating from recently
proposed language models, as described in the remainder of
this section.</p>
      <p>
        The skip-gram (SG) model involves learning
representations of tags in a low-dimensional space from post logs in
an unsupervised fashion, by using the notion of a blog post
as a “sentence” and the tags within the post as “words”,
borrowing the terminology from the Natural Language
Processing (NLP) domain (see Figure 5). Tag representations
using the skip-gram model [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ] are learned by maximizing
the objective function over the entire D set of blog posts,
      </p>
      <sec id="sec-12-1">
        <title>9gemini.yahoo.com</title>
        <p>log P(tj+m|tj).</p>
        <p>(5.1)
kg_coks
chocc
where vt and vt0 are the input and output vector
representations of tag t of user-specified dimensionality d, n defines the
length of the context for tag sequences, and T is the number
of unique tags in the vocabulary. From equation (5.2) we see
that tags that co-occur often and tags with similar contexts
(i.e., with similar neighboring tags) will have similar vector
representations as learned by the word2vec model.</p>
        <p>The semi-supervised skip-gram (SS-SG) model
assumes that some tags are labeled with categories from the
GIT taxonomy. Next, we introduce a dummy category
vector for each node of the taxonomy, and leverage the tag
contexts in blog posts to jointly learn tag vectors and category
vectors in the same feature space. Given such a setup, after
learning the representations, every tag from the vocabulary
can be categorized by simply looking up the closest category
vector in the joint embedding space.</p>
        <p>Specifically, given the labeled tags, we extend D to obtain
data set Dss where categories are imputed into post
“sentences” pi, where available. In particular, labeled tags are
accompanied by assigned categories, and every time a vector
of a labeled central tag tj is updated to predict the
surrounding tags, the vectors of categories assigned to tj are updated
as well. More formally, assuming the central tag tj is
labeled with Cj of C categories in total, ζj = {c1, . . . , cCj },
the semi-supervised skip-gram learns tag and category
representations by maximizing the following objective function,
X X</p>
        <p>X
p∈Dss tj∈p −n≤m≤n,m6=0
log P(tj+m|tj)+ X log P(tj+m|c) .</p>
        <p>c∈ζj
(5.3)
The probability P(tj+m|c) of observing tag tj+m, given label
c of the current tag tj, is defined using the soft-max,
P(tj+m|c) =
exp(vc&gt;vt0j+m )
PT
t=1 exp(vc&gt;vt0)
.</p>
        <p>(5.4)
This procedure allows us to seamlessly incorporate labeled
and unlabeled data, and learn tag and category vectors in
the joint embedding space. Then, the classification of tags
amounts to a simple nearest-neighbor search among the
category vectors. In Figure 6 we show the graphical
representation of the semi-supervised skip-gram model.
5.2.1 Training</p>
        <p>
          The models are optimized using stochastic gradient
ascent, suitable for large-scale problems. However,
computation of gradients ∇L in (5.1) and (5.3) is proportional to the
vocabulary size T , which may be computationally expensive
in practical tasks seeing as how T could easily reach several
million tags. As an alternative, we used a negative sampling
approach [
          <xref ref-type="bibr" rid="ref13">13</xref>
          ], which significantly reduces the computational
complexity.
        </p>
        <p>The data set used during the model training comprised 6.8
billion posts that contained tags. To collect category labels
for some of the tags, we sorted the tags in a decreasing order
of popularity and the editors labeled the top ones with one or
more categories. Following this process, we obtained 8,400
categorized tags. We show several examples in Table 2.</p>
        <p>
          The models were trained using a machine with 96GB of
RAM memory and 24 cores. The dimensionality of the
embedding space was set to d = 300, and the context
neighborhood size was set to n = 5. Finally, we used 10
negative samples in each vector update for negative sampling.
Similarly to the approach in [
          <xref ref-type="bibr" rid="ref13">13</xref>
          ], most frequent tags were
sub-sampled during the training.
5.2.2 Inference
        </p>
        <p>When the vector representations of all tags are learned,
we can find similar tags for a given tag by straightforward
extracted from an activity is of class k, and 0 otherwise.
In addition, we used the time stamp tact, representing the
day in which the activity happened, to exponentially decay
less recent activities to account for passing interest (we used
α = 0.99 in our experiments). Note that the set Ai, in
addition to the user’s original content, also included posts
reblogged by user ui.</p>
        <p>t</p>
        <p>The value of ui,cat=k represents an exponentially
timedecayed count of all the activities in the k-th category. To
effectively store the user profile for interest targeting, instead
of storing all possible activities and their time stamps, we
maintain a decayed sum of the activities and update the
t
ui,cat=k daily.</p>
        <p>Using this approach, we are able to qualify top K users in
t
each category by sorting the interest score ui,cat=k.
Depending on the advertiser’s goals and the category, the choice of
K varies from campaign to campaign. We note that a
single user can be qualified into one or more interest categories
(e.g., a user can be categorized in “Sport”, “Sport/Basketball”,
and “Health and Nutrition/Vitamins” at the same time),
and, when the system was deployed, each user was assigned
to 13 categories on average. An example of user profiles
qualified into certain categories is given in Table 5.
5.3.1</p>
        <p>Leveraging the follower graph</p>
        <p>To be able to target Tumblr users who do not create
much content, but who actively follow and engage with other
blogs, we leverage the follower graph to create additional
categorized features. Using equation 5.5 we can identify
frequent bloggers in certain interest categories by focusing on
a small percentage of users with a maximum ui,cat=k.
Following and liking posts created by social influencers in the
k-th category serves as additional evidence of one’s interest
in that category.</p>
        <p>In each interest category, we label the 5% of users with
the highest number of activities in that category as frequent
bloggers. Next, we update the interest score of all users ui
in the k-th category, in the following manner</p>
        <p>t
ui,cat=k+ =</p>
        <p>X X α(t−teng) weng I(b is of class k),
(5.6)
where Fi is a set of all frequent blogs followed by user ui,
eng are all engagements with the b-th blog, i.e. likes or
follow actions, along with their weights weng (e.g., if the
b∈Fi eng∈b
posts created by the b-th blog were liked ten times, then the
value was set to 10; if a user followed the b-th blog, then
the value was set to 1), while the indicator function I(·)
returns 1 if the blog is of class k, and 0 otherwise. Similarly
to other activities, we applied the exponential decay to the
sum, based on the time stamps of follow and like actions.</p>
        <p>We have observed that additional signals, in the form of
follow and like engagement with frequent bloggers, increase
our segment sizes, making it possible to efficiently target a
greater number of users.
5.4</p>
      </sec>
    </sec>
    <sec id="sec-13">
      <title>Results</title>
      <p>In order to evaluate the generated user interest segments,
we performed online A/B testing and worked with several
advertisers who ran concurrent interest-targeted and
untargeted campaigns. We tracked user engagement with their
ads in terms of sponsored post likes, reblogs and follows,
and show the results for 8 targeting campaigns in Table 6.
We observed an average increase of 20% in user engagement
(aggregate of 3 metrics) with sponsored posts in comparison
to untargeted campaigns. This performance result
represents a significant improvement over the baseline approach.
6.</p>
    </sec>
    <sec id="sec-14">
      <title>GENDER PREDICTION</title>
      <p>In this section, we explain the details of our gender
prediction model, based on the user profiles described in the
previous sections. We first describe the generation process
of a golden set of labeled users, which is used to train a
predictive model that generalizes well on the remaining
unlabeled users. This is followed by the model’s description
and a discussion of the results.
#Microposts2016
6th Workshop on Making Sense of Microposts</p>
      <p>In order to train the machine learning method for gender
prediction, in addition to user profiles, we also require
labels that present the ground truth (i.e., “male” or “female”).
However, Tumblr does not collect gender information when
users sign-up, leaving open the question of how to obtain
such data.</p>
      <p>To address this problem, we proposed to leverage highly
informative blog description data in order to infer user
gender information. In particular, very often users declare their
name in the blog description, as illustrated in Figure 1. To
extract the users’ declared names, we used several regular
expression rules that we found to result in very high
precision. The obtained results from a large set of name-matching
regular expressions were editorially tested for quality. It was
found that regular expressions reported in Table 7 yielded
the most reliable extracted names (valid names were
extracted in more than 95% of the cases). Next, in order
to generate the gender ground truth, we used the US
census data of popular baby names10 from year 1880 to 2013
to create a “name → gender” mapping. Seeing as how
certain names are given to both males and females, we used
the empirical counts of babies with certain names from
census data to generate the labels. More specifically, we used
male/female empirical ratios as soft labels, with 1 indicating
100% confidence in a male and 0 indicating 100% confidence
in a female name.
6.2</p>
    </sec>
    <sec id="sec-15">
      <title>Proposed approach</title>
      <p>
        Let Dg = {(xi, yi), i = 1, ..., N } denote our gender data
set, where N is the total number of labeled users, xi is the
K-dimensional user feature vector generated from the user
profiles, and yi ∈ [
        <xref ref-type="bibr" rid="ref1">0, 1</xref>
        ] is the user label (real-valued number,
ranging from 0 to 1). The feature vectors were generated
from the user profiles described in Section 4.2, by
disregarding time stamps (due to the fact that, unlike the users’
interests, their gender does not fluctuate), and directly using
the feature counts as values. To handle large counts, we
normalized the counts by applying log transformation:
assuming that the count is x, we replace the count by the value
log(1 + x).
      </p>
      <p>Our goal is to learn a gender-predictive model, f : x →
y. As a classification model, we used logistic regression,
parameterized by weight vector w. We assume that the
posterior gender probabilities can be estimated as a linear
10www.ssa.gov/oact/babynames/limits.html
and P(y = 0|x) = 1 − P(y = 1|x). To estimate the
parameters w, we minimize the following loss function,</p>
      <p>N
min 1 X
w∈RK N i=1</p>
      <p>yi − f (xi, w) 2 + λkwk1,
where hyper-parameter λ controls the `1-regularization,
introduced to induce sparsity in the parameter vector and
reduce the feature space to a subset of features that are the
most predictive. For data sets with a large number of
features, as we have in our use case, it is common that many
features are not useful for producing the desired learning
result. For this reason, the `1-regularization was a critical
part of our training procedure. In addition, we
experimentally observed that the model generalizes better when we
trained an initial model with `1-regularization to find which
features have non-zero weight, and then do another round
of training without `1-regularization, by only using features
with non-zero weights from the first round to learn a better
classifier.</p>
      <p>
        Given a trained logistic regression model, the posterior
class probabilities are estimated as f (xi, w) ∈ [
        <xref ref-type="bibr" rid="ref1">0, 1</xref>
        ]. Then,
the classification predictions are made by thresholding, as
yˆi = sign(f (xi, w) − θ), where threshold θ is set between 0
and 1 to ensure the desired precision and recall according to
specific advertisers requirements.
6.3
      </p>
    </sec>
    <sec id="sec-16">
      <title>Results</title>
      <p>
        To evaluate the accuracy of our gender prediction
framework, we trained a logistic regression model on 70% of the
golden set and tested on the remaining 30%. We used the
Vowpal Wabbit [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ] implementation on Hadoop to train the
model. To illustrate the performance of our gender
classifier, the performance results in terms of precision and recall
measures are presented in Table 8. The threshold value θ
was set to a value which ensured precision of 0.8.
      </p>
      <p>In addition to evaluation on the hold-out set, we also
editorially evaluated gender predictions on the unlabeled data
set of user profiles. We randomly picked 1,007 gender
predictions from the population of 64.1 million users and asked
editors to visit their profiles and verify their gender. They
were instructed to mark our predictions as “correct”,
“incorrect”, or “not sure”. The “not sure” grade is to be used when
the visual inspection of a profile is inconclusive, as we found
was often the case. The editorial judgment came back with
573 “correct” (429 females and 144 males), 9 “incorrect”, and
425 “not sure” grades (see Table 9). The fact that there are
so many “not sure” grades indicates that in many cases it
is hard to infer the gender even after manual efforts,
further indicating the benefits of the proposed approach and
its superior performance in comparison to humans. Finally,
we retrained the model with 100% of the golden set and
deployed it in Yahoo production systems.</p>
      <p>A demonstration video of the most predictive tags
in each gender group is available online at https://www.
youtube.com/watch?v=jXGJ0TpOlhg.</p>
    </sec>
    <sec id="sec-17">
      <title>DEPLOYED SYSTEM</title>
      <p>Due to the rapid growth of Tumblr and the large number
of activities generated by the existing users, we implemented
daily scoring of users in Yahoo production servers. We store
the activities, i.e. raw counts as well as decayed counts,
in Hive tables11 for efficient retrieval. The decayed counts
used in interest prediction are updated on a daily basis by
multiplying the old feature values by the decay factor α and
adding new activities. In order to infer the gender of new
users we implemented daily scoring by leveraging
MapReduce on Hadoop12. Both interest and gender models are
retrained on a regular basis.</p>
      <p>After thorough editorial evaluation of the inferred
gender and interest targeting, both targeting frameworks were
enabled through Gemini self-serve tool13. Advertisers can
choose to use gender and/or interest targeting with custom
segment sizes, allowing for effective targeting campaigns.</p>
    </sec>
    <sec id="sec-18">
      <title>CONCLUSIONS</title>
      <p>We have presented the steps in the development of a
largescale Tumblr gender and interest targeting framework, where
we used historical Tumblr activities to create rich user
profiles. We described the methodology, including a novel
semisupervised neural language model, as well as the high-level
implementation details behind the deployed system.
Currently, our gender and interest predictions cover users that
generate more than 90% of Tumblr’s daily activities, and
are heavily leveraged by advertisers. In our ongoing work,
we are concentrating on creating custom keyword-targeted
advertising segments, specifically tailored for a particular
advertiser, which include addressing of the problems of
keyword discovery and expansion.</p>
    </sec>
  </body>
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