1. Confirmation bias
Reliability of cognitive processes: Biases in thinking and decision-making

2. What is confirmation bias?
the tendency to search for, interpret, favour, and recall information or evidence that substantiates one's pre-existing beliefs or hypotheses and can lead to poor decision- making.
Example: The Mathematician
Schema: expectation - unemotional, lacking social skills, strange sense of humour.
Selective remembering: remember things that confirm our beliefs/ignore info that contrasts with schema
e.g. remember: rather quiet, failed to laugh when someone made a joke; ignore that he spoke warmly about his daughter, maintained good eye contact.
Leads us to draw unhelpful conclusions, poor decisions, e.g. do not seek out this man in future, miss out on a potential new friend.

3. Link to system 1 thinking
CB may have evolved to help us cope with the intensity and sheer volume of information from the senses
We cope by instinctively deploying ‘system one’ thinking, (Stanowich and West ) - fast and without conscious awareness
no control over this style of thinking, ‘forced’ to ignore information that does not fit with prior knowledge
focus on limited array of details that confirms pre-existing sense of reality before putting in effort to discover contradictory evidence.
Fiske and Taylor (1984): humans as ‘cognitive misers’, avoid expending time and effort on cognitive tasks instead use heuristics (mental short cuts)

4. Example of CB in Action: Medicine
Can lead to devastating consequences in medicine; misdiagnosis - incorrect treatment, further health complications or even death.
Doctors selectively attend to information that confirms preliminary diagnosis, failing to attend to contradictory signs and symptoms suggestive of different diagnoses
Example: Patient diagnosed with migraine due to symptoms of headaches, doctor may not pick up on signs of forgetfulness or co-ordination problems, symptoms of brain tumour.
Doctors may ask leading questions
patient then primed to provide information that fits with the doctor’s expectations
e.g. do have any visual disturbance prior to the headache coming on?

5. Mendel et al. (2011) - Aim
To show how confirmation bias can affect the validity of psychiatric diagnoses.
Specifically, whether confirmation bias limits the search for new information once a preliminary diagnosis had been made
How this affects final diagnosis and treatment recommendations.

6. procedure Method: Quasi-experiment
IV: Level of experience: Psychiatrists and medical students
Hypothesis: Less experienced student group would be more prone to confirmation bias than more experienced group (psychiatrists)
75 psychiatrists (44 men, 31 women, average age 35, with average of 6 years professional experience) from two state and one university hospital
75 fourth-year medical students (31 men, 43 women, average age 25) who were completing a one-week internship in a psychiatric hospital.

7. Procedure cont’d…
Pps shown a vignette about a 65-year-old male patient with depressive symptoms who had been admitted to a psychiatric hospital due to an overdose.
Pps had to make a preliminary diagnosis:
Alzheimer’s or severe depressive episode
96% initially diagnosed depression
Next, Pps given the option of receiving access to further information about the patient.
12 summary statements, 6 relating to Alzheimer’s and 6 to depression
asked to tick which ones they would like to read in full
summaries included sentences such as ‘A hint of the presence of Alzheimer’s disease could be that the patient shows memory problems’
if the participants ticked this option they would then be given more detailed notes of around 150–175 words.

8. Procedure Detailed chunks of information presented one at a time
participants allowed as many pieces of further information as they wished before making their final diagnosis and suggest treatment plan
The detailed information was strongly suggestive of Alzheimer’s and not depression, unlike the summary statements which were deliberately more balanced.
DVs:
1. how many pieces of further information were requested
2. whether the participants’ information search was …
confirmatory (they asked for at least one more piece of information, linked to their initial diagnosis)
balanced (they asked for the same number of pieces of information linked to the two diagnoses)
disconfirmatory (they asked for at least one more piece of information linked to the alternative diagnosis).

9. Findings
Number of pieces of additional information requested did not differ significantly between the psychiatrists and the students (the mean was 8/12 for both groups).
However, psychiatrists were significantly more likely to ask for disconfirmatory items of information, than confirmatory items (p< 0.001)
students’ information search was more balanced, although this was not significant, p=0.23.
13% of psychiatrists and 25% of students showed confirmation bias when searching for new information
participants conducting a confirmatory information search were significantly less likely to make the correct diagnosis compared to participants searching in a disconfirmatory or balanced way.
70% of psychiatrists and 63% of student who used the confirmatory style ended up making the wrong diagnosis.
The number of information items searched significantly predicted diagnostic accuracy; participants selecting six or less items showing poorer diagnostic accuracy than participants selecting more than six items.
Participants who chose the wrong diagnosis also prescribed different treatment options compared with participants who chose the correct diagnosis.

10. Conclusions
Clear evidence that confirmation bias can affect decision-making in the field of psychiatry
confirmation bias more common in inexperienced thinkers compared with experts
possibly explained by cognitive dissonance theory, i.e. if people think that a certain outcome is the case e.g. the patient has depression, then being confronted with contradictory evidence (the patient is showing signs and symptoms of Alzheimer's) creates an cognitive dissonance
CD is reduced without the challenges of changing one’s original position, by searching for additional supportive evidence whilst ignoring information to the contrary.