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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>Irish Journal of Medical Science (1971</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.1007/s10354-017-0570-6</article-id>
      <title-group>
        <article-title>Formalizing Cognitive Biases in Medical Diagnostic Reasoning</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Dominik Battefeld</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Stefan Kopp</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Social Cognitive Systems Group, Bielefeld University</institution>
          ,
          <addr-line>Inspiration 1, 33619 Bielefeld</addr-line>
          ,
          <country country="DE">Germany</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2022</year>
      </pub-date>
      <volume>12513</volume>
      <fpage>0000</fpage>
      <lpage>0002</lpage>
      <abstract>
        <p>This paper presents preliminary work on the formalization of three prominent cognitive biases in the diagnostic reasoning process over epileptic seizures, psychogenic seizures and syncopes. Diagnostic reasoning is understood as iterative exploration of medical evidence. This exploration is represented as a partially observable Markov decision process where the state (i.e., the correct diagnosis) is uncertain. Observation likelihoods and belief updates are computed using a Bayesian network which de nes the interrelation between medical risk factors, diagnoses and potential ndings. The decision problem is solved via partially observable upper con dence bounds for trees in Monte-Carlo planning. We compute a biased diagnostic exploration policy by altering the generated state transition, observation and reward during look ahead simulations. The resulting diagnostic policies reproduce reasoning errors which have only been described informally in the medical literature. We plan to use this formal representation in the future to inversely detect and classify biased reasoning in actual diagnostic trajectories obtained from physicians.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Diagnostic reasoning</kwd>
        <kwd>Cognitive bias</kwd>
        <kwd>Cognitive model</kwd>
        <kwd>POMDP</kwd>
        <kwd>Bayesian network</kwd>
        <kwd>Epilepsy</kwd>
        <kwd>CDSS</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        gold standard tests exists to con dently con rm or rule out epilepsy as a diagnosis candidate [3,
p. 144]. Additionally, the isolated presence or absence of a semiological feature cannot warrant
a diagnostic decision towards or against epilepsy [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Information is mainly obtained through
subjective, personal dialogue rather than objective test results [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ] and consequently, evidence
quality su ers from inaccurate memory retrieval and miscommunication. The diagnosis of
seizure-like events is thus a prime example of the initially mentioned incompleteness and
uncertainty inherent to medical decisions. Today, the most successful approach to diagnose epilepsy
and thus solve the medical decision problem is e cient knowledge exploration, i.e., detailed
history taking, critical eyewitness report analysis and conservative test result interpretation
[
        <xref ref-type="bibr" rid="ref3 ref4 ref5">3, 5, 4</xref>
        ]. By that, experts learn to maneuver in the space of retrievable medical evidence. The
sequence of questions they ask, features they query and tests they issue de nes one possible
diagnostic trajectory through this space and the overall goal is not to cover everything but
everything relevant.
      </p>
      <p>
        In the endeavour to ease diagnostic pressure on physicians in highly complex domains like
these, clinical decision support systems (CDSS) provide assistance in various ways for both
doctors and patients [
        <xref ref-type="bibr" rid="ref6 ref7">6, 7</xref>
        ]. Some try to increase the certainty of information by tracking and
storing features about speci c seizures [8, p. 98]. Others facilitate information integration.
They act as di erential diagnosis generators which accept a set of present medical ndings and
test results and output candidate diagnoses along with their respective probability [
        <xref ref-type="bibr" rid="ref10 ref11 ref9">9, 10, 11</xref>
        ].
What these state-of-the-art systems lack is an explicit model of their user. They can be queried
for additional information but are agnostic to the reasoning process in the physician’s mind.
Thus, some argue that the development paradigm of clinical decision support systems should
shift from resembling an additional uncertain source of information (i.e., “Is the system output
correct?”) towards facilitating the process itself in a clinical reasoning support system [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ].
This is especially evident in the fact that most diagnostic errors are not rooted in insu cient
medical knowledge or expertise, but rather in structural causes like time pressure and cognitive
biases like premature closure [
        <xref ref-type="bibr" rid="ref13 ref14">13, 14</xref>
        ]. Additionally, reasoning errors are especially prevalent
in areas of high subjectivity like epilepsy. It su ers from an interobserver variation, where
multiple practitioners don’t agree in their diagnosis of the same patient. Misdiagnosis rates are
estimated around 23% or even higher in everyday practice [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ].
      </p>
      <p>
        Taken all together, the goal of this paper is to formally de ne the relation between a speci c
cognitive bias (i.e., premature closure, con rmation bias and availability bias) and the erroneous
knowledge exploration trajectory leading up to the diagnostic reasoning error that may result
from it. Premature closure describes the tendency to submit an unjusti ed diagnosis too early
while a con rmation bias leads to a skewed interpretation of observations [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]. Even con icting
evidence is seen as in line with the current beliefs. An availability bias causes physicians to
favor what is familiar by overestimating the likelihood of hypotheses that “readily come to
mind” [15, p. 777]. We capture this faulty reasoning in a partially observable Markov decision
process (POMDP) by altering rewards and observation likelihoods during belief update and
policy computation. Here, the idea of a biased policy computation is based on the premise that
planning always involves a predictive component of what happens next after executing some
action. If the understanding of the world is in itself biased, mental action execution during
planning will lead to biased world states which will manifest in biased action assessment and
thus in a biased policy. To explain this approach in more detail, Section 2 presents related
work on the formalization of diagnostic processes and cognitive biases in diagnostic reasoning.
Section 3 introduces the cognitive modeling work and how each bias can be integrated into
it. Section 4 presents the resulting policies under each bias and Section 5 concludes with a
discussion of the results, potential shortcomings and next steps.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Related work</title>
      <p>
        In general, POMDPs “model sequential decision making problems where the agent must act under
partial observability of the environment state. POMDPs consider both uncertainty in action e ect
(i.e., transitions) and observations, which are usually incomplete and noisy information related to
the state” [16, p. 2]. They are are a well known and frequently used formalism to operationalize
medical decision-making in various domains. In practice, Zhang et al. [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ] model the diagnostic
process and subsequent management of chronic diseases in the example domain of coronary
heart disease by maximizing the patient’s total expected quality-adjusted life years (QALYs).
They focus on deriving structural properties like diagnostic thresholds and the optimal age for
a screening. Similarly, Zhang et al. [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ] propose a non-stationary POMDP to model medical
screening for prostate biopsy referral decisions. Their model maximizes expected
qualityadjusted life years as well and incorporates prostate-speci c antigen test results as observations
within the formalism. Li et al. [
        <xref ref-type="bibr" rid="ref19">19</xref>
        ] motivate the usage of a partially observable Markov chain to
assess di erent screening strategies during colonoscopy. By optimizing parameters like initial
screening age or screening frequency, they aim to increase the diagnostic accuracy of colorectal
cancer. Arruda et al. [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ] try to mathematically de ne a stochastic shortest path policy of
tests to con rm or discard a disease hypothesis. Their approach uses Bayesian inference to
turn an a priori disease probability into posterior probabilities that warrant either immediate
treatment or a not-ill diagnosis. Partially observable Markov decision processes are also used to
infer a suitable medical treatment policy. Here, Bazrafshan et al. [
        <xref ref-type="bibr" rid="ref21">21</xref>
        ] use a nite-horizon MDP
to formalize the problem of planning chemotherapy and optimal drug administration to treat
gastric and gastroesophageal cancers. Hauskrecht et al. [
        <xref ref-type="bibr" rid="ref22">22</xref>
        ] employ the POMDP framework
“to model and solve the problem of the management of patients with ischemic heart disease” [22,
p. 221]. Ibrahim [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ] use the decision framework in two separate phases. A rst POMDP model
formalizes the physicians explorative process to understand how sensitive the patient reacts
to a medication with warfarin. Then, a second MDP model is used to calculate the optimal
treatment policy of the patient with warfarin based on the beliefs and sensitivities derived from
the rst stage.
      </p>
      <p>
        We adopt these previous approaches in which the potential state of the patient forms the
state space [
        <xref ref-type="bibr" rid="ref17 ref18 ref19">17, 18, 19</xref>
        ]. Sequential action selection is based on the current subjective belief
in each possible patient state and obtained medical information updates the belief after each
action using the Bayes calculus. Using a POMDP enables us to represent the current belief
and its update in an e cient and transparent manner at each time step. We share the view of
Arruda et al. [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ] to frame a diagnosis as a stochastic shortest path problem of information
retrieval actions up to a diagnosis submission as the point at which “su cient justi cation” is
reached. This connects to our idea of economically exploring the space of available medical
knowledge to only query features that are relevant at this point in time and neglect redundant
or insigni cant ones. This trade-o between acquiring more information to increase certainty
and making a diagnosis as fast as possible to decrease su ering is implicitly represented in the
policy computation.
      </p>
      <p>
        Diagnostic errors induced by cognitive biases are an increasingly explored eld of research.
The shortcomings of the pioneering work on modelling diagnostic reasoning as a whole by
Elstein et al. [
        <xref ref-type="bibr" rid="ref24">24</xref>
        ] back in 1978 led to a general discussion about the cognitive representation of
medical knowledge and expertise in the mind of a trained physician. Improvement ideas gave rise
to non-analytical reasoning processes like pattern recognition [25, p. 440] and recently proposed
models of clinical reasoning acknowledge the presence of such heuristic shortcuts mostly
framed as System 1 thinking [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ]. Thus, there is a tight connection between proposed models of
reasoning in the medical domain and Kahnemann’s book on "Thinking, fast and slow" [
        <xref ref-type="bibr" rid="ref27">27</xref>
        ] up
to the point that it inspired Coughlan et al. to publish a review on "Diagnosing, fast and slow"
which ultimately concludes that “Cognitive biases are ubiquitous, even among experts. Doctors
do not di er in this regard” [28, p. 5]. More detailed analyses have identi ed approximately
50 di erent biases a ecting a physician during clinical reasoning [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ]. Among these the ones
which have been studied most extensively in the eld of diagnostics are an availability bias
[
        <xref ref-type="bibr" rid="ref14 ref15 ref30 ref31 ref32 ref33 ref34">30, 14, 31, 32, 33, 34, 15</xref>
        ], con rmation bias [
        <xref ref-type="bibr" rid="ref14 ref15 ref34">14, 35, 15, 34</xref>
        ], premature closure [
        <xref ref-type="bibr" rid="ref13 ref14 ref15">14, 13, 15, 36</xref>
        ],
overcon dence [
        <xref ref-type="bibr" rid="ref14 ref34">37, 14, 34, 35</xref>
        ], anchoring bias [
        <xref ref-type="bibr" rid="ref15 ref32 ref34">38, 15, 34, 36, 32</xref>
        ] and a representativeness
heuristic [
        <xref ref-type="bibr" rid="ref15 ref32 ref34">39, 38, 15, 32, 34, 40</xref>
        ].
      </p>
      <p>Moving away from the descriptive and empirical level to examine cognitive biases, little
research has been conducted on a formal decision-theoretic formalization of each one. In
a resource allocation problem called police patrol hour assignment, Wu et al. introduce “a
general framework for deceiving adversaries with bounded rationality in terms of the obtained
reward minimization” [41, p. 6] by leveraging prospect theory [42] to compute a biased reward
function of a human opponent. Then a MDP-based control policy is derived to exploit the
di erences between the environments objective and the adversary’s subjective reward for
maximal deception. Zhang et al. [43] apply deceptive kernel functions to observations emitted
in a POMDP model to trick the agent in establishing false beliefs about the environment. And
Bilinski et al. speculate on demonstrating bias in a cyber deception game by “exploration of game
parameters [...] to associate the outcome of algorithms to that of human decision-making biases”
[44]. More speci cally, they suggest adaptations to their domain to potentially incorporate a
gambler’s or sunk cost fallacy.</p>
      <p>Overall, there is a growing interest in understanding and measuring cognitive biases during
medical diagnosis over recent decades. While research on this topic is extensive on the
descriptive level, and rising on the empirical level, our approach is - to the best of our knowledge - the
rst to operationalize cognitive biases in a formal decision-theoretic framework like Markov
decision processes with the goal to deliberately reproduce cognitive reasoning errors during
medical diagnosis.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Modeling diagnostic reasoning</title>
      <p>The idea behind the modeling approach is to capture the problem of medical diagnosis in a
POMDP and then exploit the transparency in the formalism to integrate biased components</p>
      <sec id="sec-3-1">
        <title>Feature observation</title>
      </sec>
      <sec id="sec-3-2">
        <title>Observation likelihood</title>
      </sec>
      <sec id="sec-3-3">
        <title>Belief</title>
      </sec>
      <sec id="sec-3-4">
        <title>Medical domain model</title>
      </sec>
      <sec id="sec-3-5">
        <title>Generator model</title>
      </sec>
      <sec id="sec-3-6">
        <title>Query action END</title>
      </sec>
      <sec id="sec-3-7">
        <title>Submit action</title>
      </sec>
      <sec id="sec-3-8">
        <title>Simulations</title>
      </sec>
      <sec id="sec-3-9">
        <title>Search tree</title>
        <p>into the decision problem representation. As sketched in Figure 1, the agent can decide to
query speci c medical information which is then sampled from the medical domain model.
The obtained information updates the belief through its likelihood to be observed given each
diagnosis and the agent simulates possible next queries to choose the most suitable one at the
current step in the process. This cycle of information retrieval repeats until the agent submits
a diagnosis. Biases can manifest either in the retrospective evaluation of observations in the
belief update or the prospective assessment of potential actions. As visualized in Figure 1 both
cases are tied to the generator model. With this broad overview at hand, Section 3.1 sheds light
on how the medical domain model is de ned and used for sampling, Section 3.2 de nes the
resulting POMDP with all of its components and Section 3.3 elaborates on the modi cations
made to the generator model for each cognitive bias.</p>
        <sec id="sec-3-9-1">
          <title>3.1. Medical domain model</title>
          <p>
            We use a Bayesian network to model the medical domain stochastically. In general, Bayesian
networks represent a joint probability distribution over a nite set of discrete random variables
and enable exible inference of prior or conditional distributions over node values [45]. Our
network de nes how medical features in uence others, i.e., how diseases are caused and how
diseases present themselves in form of symptoms. While there is a causal connection between
disease and ndings, observations might di er from patient to patient. It therefore makes sense
to model the e ect of a disease with a joint probability distribution over possible diagnoses
and medical ndings. The structure of the network is derived from the work of Richens et
al. [46] who propose a three layer disease model where the top layer describes medical risk
factors, the mid layer all diseases and the bottom layer potential symptoms. The nodes for
risk factors and symptoms are derived from the work of Wardrope et al. [
            <xref ref-type="bibr" rid="ref2">2</xref>
            ]. They conducted
a study on the prevalence of medical features among patients su ering from either epileptic
seizures, syncopes or psychogenic non-epileptic seizures. Through an iterative random forest
approach, they calculated that 36 features were enough to optimally predict the disease of a
patient. Each of these features is adopted as one binary node in the network - except whether
or not the patient had a brain tumor because the sample size was too low. Features concerning
          </p>
        </sec>
      </sec>
      <sec id="sec-3-10">
        <title>Poor coordination</title>
      </sec>
      <sec id="sec-3-11">
        <title>Febrile seizures</title>
      </sec>
      <sec id="sec-3-12">
        <title>Diagnosis</title>
      </sec>
      <sec id="sec-3-13">
        <title>Violent shaking</title>
      </sec>
      <sec id="sec-3-14">
        <title>Oral automatisms</title>
        <p>
          ... 31 more ...
the general medical history of the patient count as risk factor in the top layer, other features
about the semiology of a speci c seizure count as symptom in the bottom layer. Having su ered
from febrile seizures in the childhood is thus considered a risk factor while violently shaking
during a seizure is a symptom. The parameters of each node are calculated as a maximum
likelihood estimate from the prevalence data presented in the paper [
          <xref ref-type="bibr" rid="ref2">2</xref>
          ]. This ensures, that the
nal medical domain model (see Figure 2) captures actual medical relations from the real world.
With this model at hand, we can run the variable elimination algorithm [45] to exibly compute
the likelihood P (fn+1|d, f1, . . . , fn) of any feature fn+1 given a speci c diagnosis d and a set
of already known features f1, . . . , fn.
        </p>
        <sec id="sec-3-14-1">
          <title>3.2. Diagnostic process model</title>
          <p>We use a POMDP to model the diagnostic reasoning process. It is formally de ned as the tuple
hS, A, O, T, Z, R, γi, where S is a set of states, A is a set of actions and O a set of observations.
T de nes the transition model from one state to the next, Z de nes the probability of emitting
an observation given the current state and action and R likewise describes the probability
of emitting reward given the current state and action. γ is a discount factor to decrease the
in uence of reward collected far in the future.</p>
          <p>In our context, a diagnosis is understood as the sequential exploration of medical ndings up
to a point where the agent is su ciently certain to commit itself to one of multiple options. The
agent holds an initially uniform belief distribution over all three diagnostic options. Then, the
agent is able to query for medical information (i.e., risk factors and symptoms in the medical
domain model) and obtains uncertain observations (i.e., a sampled value for this node from the
medical domain model). The crucial decision to make at each step is which medical feature to
query next. Solving the POMDP for a diagnostic policy thus de nes one trajectory through
the space of available medical knowledge. After receiving the feature observation the agent
updates its belief state depending on the likelihood of observing such a feature value in a patient
given each diagnosis and the interaction loop starts again (see Figure 1). At any point in time,
the agent can submit a speci c diagnosis and by that end the whole process. Derived policies
are therefore expected to exhibit a trade-o between gathering valuable information about
the patient to reduce uncertainty and keeping the diagnostic process as short and e cient as
possible.</p>
          <p>
            We solve the POMDP problem via partially observable upper con dence bounds for trees in
Monte-Carlo planning (PO-UCT) [47] using the Python library pomdp_py [
            <xref ref-type="bibr" rid="ref16">16</xref>
            ]. This algorithm
is essentially an adapted version of a Monte-Carlo tree search where state nodes in the tree
are replaced by histories and the greedy action selection is adjusted for already encountered
nodes in the tree. For unknown nodes, we use a uniform random action selection. At each
time step, the agent runs simulations by sampling a current state from its belief state and
then repeatedly using a generator model to simulate transitioning to state s0 and obtaining
observation o and reward r after executing action a in state s in each trajectory. After all
simulations, the agent executes the action that reached the maximum expected return in the
search tree. In the following, we will introduce each POMDP component in more detail.
State space Each state s ∈ S is de ned by the true diagnosis the patient is su ering from (i.e.,
epileptic seizure, syncope or psychogenic non-epileptic seizure) and a predicted diagnosis by the
agent. This predicted diagnosis is null as long as the process is running and is set accordingly
once the agent commits itself. Thus, states where the true diagnosis and the predicted diagnosis
are set are terminal states.
          </p>
          <p>Action space Each action a ∈ A has one of two types. There are query actions to ask for
speci c information (one query action for each risk factor and symptom) and submit actions
to commit oneself to one option (one for each disease). For example, executing query febrile
seizures means to ask the patient whether he has ever su ered from febrile seizures.
Observation space Each observation o ∈ O is associated with a node in the medical domain
model. After query actions, the observation holds the queried feature and a value of that feature.
Observing febrile seizures = no thus means that the patient has not su ered from febrile seizures
in the past. After submit actions, the observation just holds the submitted diagnosis as the
process ends.</p>
          <p>Transition model Query actions do not change the state. Submit actions lead to a
deterministic transition into a terminal state, where the predicted diagnosis is set accordingly. Once the
agent is in a terminal state, no transitions are possible.</p>
          <p>Observation model The likelihood P (o|s0, a) of obtaining observation o after transitioning
to state s0 via query action a is computed using the medical domain model. The distribution
over all values of the queried feature is conditioned on the true diagnosis d in the state and the
medical evidence o1, . . . , on obtained thus far from previous observations. The next feature
value for observation on+1 is then sampled from P (on+1|d, o1, . . . , on). Observations after
submit actions are deterministic.</p>
          <p>Reward model Executing query actions triggers a reward of −1 to incentivise a short
diagnostic trajectory that does not query more features than necessary. Submit actions are
rewarded with +100 for a correct diagnosis (i.e., true and predicted diagnosis in the state match)
and −100 for a wrong one.</p>
          <p>Generator model The generator model is used during simulations to generate a successor
state s0, an observation o and a reward r when mentally executing action a in state s. It reuses
the observation model to infer the likelihood of a feature value P (o|s0, a) to sample from it.
Query actions again lead to a reward of −1. As the agent cannot know the true diagnosis during
simulation, the reward for submit actions di ers from the true reward model. Here, reward
is dependent on the entropy in the belief state. If the agent submits the diagnosis it is most
convinced of and the normalized entropy in its belief state is below 0.25, then it collects a reward
of +100 and −100 otherwise to penalize unjusti ed diagnoses under high uncertainty.</p>
        </sec>
        <sec id="sec-3-14-2">
          <title>3.3. Modeling cognitive biases</title>
          <p>We simulate cognitive biases with the diagnostic policy via adjustments to the generator model
during planning with PO-UCT. As mentioned earlier, the agent determines the next action
to execute at a given time step by running multiple simulations from the current belief state.
The evolution of these simulated trajectories is determined by the generator model G. Now if
the environment de nes a ground truth transition model T , observation model Z and reward
model R, then cognitive biases manifest themselves in conceptual deviations from T , Z and
R in G. In a cognitive sense, the agent exhibits a biased policy because its understanding of
the environment and thus its mentally derived action outcomes are biased. To exemplify the
e ects of biases in the generator model, we integrate three of the most common cognitive biases
associated with medical diagnoses: an availability bias, a con rmation bias and premature
closure (see Section 2). In the following, we will explain the integration of each in more detail.
Availability bias “The disposition to judge things as being more likely, or frequently occurring,
if they readily come to mind. Thus, recent experience with a disease may in ate the likelihood of
its [sic] being diagnosed” [15, p. 777]. Neurologists may overestimate the prevalence of epileptic
seizures where clinical psychiatrists tend to see psychogenic non-epileptic seizures as both draw
expertise from past experience with either disease. We implement this bias during belief updates
by using a skewed observation likelihood in the generator model. Before applying the update,
each likelihood is scaled according to how “readily the corresponding diagnosis hypothesis
comes to mind”. The bias always targets one of the three options. Observation likelihoods given
this diagnosis are scaled by 0.4 and others are scaled by 0.3, expressing a constant preference
towards one available diagnosis.</p>
          <p>Confirmation bias “This entails underestimating information that does not t one’s hypothesis”
[14, p. 3]. Because this bias again a ects the integration of new evidence into the current belief
state, it is implemented similarly to the availability bias. We again target the agent’s belief
update by skewing the likelihood of observations in the generator model, but this time the
likelihood of an observation given a speci c diagnosis is not scaled by a xed amount, but by
the current belief of the agent in that particular diagnosis. Thus, it is harder for new evidence to</p>
        </sec>
      </sec>
      <sec id="sec-3-15">
        <title>None Availability bias Confirmation bias Premature closure</title>
        <p>alter the current belief states. Con rming observations are over- and contradictory observations
are underestimated.</p>
        <p>Premature closure “The tendency to apply premature closure [...] accepting a diagnosis before
it has been fully veri ed” [15, p. 778] This bias manifests in the process if the agent commits itself
to one diagnosis although the entropy in the belief state is too high to justify that. Consequently,
we implement this bias by increasing the normalized entropy threshold in the generator model
at which the agent is able to collect positive reward for a diagnosis submission from 0.25 to 0.75.
This leads to the submission of unveri ed, uncertain diagnoses early in the process.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Experiments</title>
      <p>To demonstrate the resulting policies under each bias, we run and track 30 diagnostic trajectories
(10 for each di erential diagnosis) for each possible variant of the agent: unbiased, availability
biased towards epileptic seizures, availability biased towards psychogenic seizures, availability
biased towards syncopes, con rmation biased and a ected by premature closure. For computing
the next action to execute, we run 200 simulations at each time step via PO-UCT planning with
a maximum depth of 50 during tree search, an exploration constant of 1.0 and a discount factor
of 0.9.</p>
      <p>
        Unbiased Among all variants, the unbiased agent achieves a diagnostic accuracy of 86.7%
(see Table 2) which is comparable to the 86.0% reported by Wardrope et al. [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] on the same data
set that has been used to learn the parameters of the medical domain model. During diagnosis,
the agent exhibits no particular preference for speci c risk factors or symptoms (see Figure 3)
and revises its diagnostic belief over time by changing its main hypothesis (see Figure 4).
Availability bias In contrast to unbiased policies, agents with an availability bias focus
on a subset of features during knowledge exploration (see Figure 3). While the length of
each diagnostic process is comparably long to not having any bias (see Table 1), a previous
familiarity with epileptic seizures leads to a focus on limp limbs and oral automatisms. A similar
e ect is observable for psychogenic seizures (focused on deja-vu and impaired awareness)
and syncopes (focused on poor coordination and rapid head turning) but the e ect remains
strongest for epileptic seizures. Concerning diagnostic performance, an agent primed towards
epileptic seizures misdiagnoses nearly all cases of psychogenic seizure (9/10) and vice versa
the agent primed towards psychogenic seizures even declares all cases of epileptic seizures
as psychogenic. This e ect is absent for the diagnosis of syncopes which may be caused by
the closer similarity between epileptic and psychogenic seizures. Wardrope et al. [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] report a
similar e ect concerning confusion matrices between all three diagnoses, where all syncopes
are identi ed correctly while epileptic and psychogenic seizures are mixed up more often.
      </p>
      <p>Bias</p>
      <sec id="sec-4-1">
        <title>None Availability bias Confirmation bias Premature closure</title>
        <p>Confirmation bias A con rmation bias leads to short and unsuccessful diagnostic processes
(see Table 1 and 2). The agent typically follows its rst main hypothesis and after a few steps
con rms itself more and more into wrong diagnoses. As opposed to the unbiased model, the
policy is not able to recover from misleading belief states, that would need to be reverted upon
contradictory information (see Figure 4).</p>
        <p>Premature closure Similar to a con rmation bias, trajectories a ected by premature closure
are very short. But resulting policies still perform remarkably well in terms of accuracy (see
Table 2). In a vital di erence to the con rmation bias, the diagnostic process is therefore not
impaired at the stage of information integration, the agent simply does not collect enough
information to integrate.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Conclusion</title>
      <p>In conclusion, this paper proposes that cognitive biases are rational behaviour in misunderstood
environments. Formalizing a cognitive bias during diagnostic reasoning means distorting the
true environment to render the biased policy as optimal policy. We achieve these distortions by
skewing rewards and observation likelihoods during belief updates, but any modi cation to
the environment would be viable in principle. Agents could neglect parts of the state or action
space or dynamically grow the proportions of action they know. We justify this perspective by
the fact that planning in itself always requires some mechanism for mental outcome prediction.
If these outcome predictions are based on wrong assumptions, planning will produce biased
strategies.
No bias</p>
      <p>Availability bias (ES)
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0</p>
      <p>
        As we have shown, partially observable Markov decision processes in combination with
Monte-Carlo planning methods have proven as a suitable framework to implement these ideas
in an explainable fashion. By manipulating the generator model, biases due to skewed Bayesian
reasoning can be explicitly represented. Agents with an availability bias are deceived into
misdiagnoses of similar diseases (epileptic vs. psychogenic seizures), con rmation biased
physicians tend to arrive at a fast and mostly wrong diagnosis and premature closure can
be induced by rewarding prematurely. But the approach in general is at a rather early stage
and will need much more investigation. How this approach relates to modeling the proposed
System 1 and 2 processes during diagnosis [
        <xref ref-type="bibr" rid="ref28">28</xref>
        ] explicitly will require further research especially
with regard to cognitive plausibility. At the moment, a simplistic Bayesian network as medical
domain model is used, where only 35 features are integrated and each feature can only be
present or absent. The patient always su ers from one of three diseases. We plan to enhance
the current approach with an empirical study to collect diagnostic trajectories from physicians.
Analyzing their queries and diagnostic strategies will enable improvements to both the medical
domain model and the process model. Overall, the presented work contributes to empowering
diagnostic reasoning support systems to detect and potentially classify erroneous diagnostic
reasoning. As we can only x what we understand, identifying the error cause is a rst important
step towards resolving misdiagnoses altogether.
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      <p>S</p>
      <p>Queried feature
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      <p>Epileptic seizure
Psychogenic seizure
Syncope
Epileptic seizure
Psychogenic seizure
Syncope
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    </sec>
    <sec id="sec-6">
      <title>Acknowledgments</title>
      <p>Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation): TRR
318/1 2021 – 438445824.</p>
    </sec>
  </body>
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