This document discusses various types of bias that can occur in research studies. It defines bias as an unknown or unacknowledged error created during the research process. Some key biases discussed include selection bias, measurement bias, confounding, and publication bias. The document emphasizes the importance of research design features like randomization and blinding to help reduce bias.

1. Steven Moustafa Kassem

2. Steven Moustafa Kassem

3. unknown or unacknowledged error created
during the design, measurement, sampling,
procedure, or choice of problem studied

4. ◦ bias is so pervasive because we want to confirm our
beliefs
◦ science is organized around proving itself wrong
not right
◦ key difference between qualitative and quantitative
research is
 attempts to eliminate bias by quantitative researcher
 explicit acknowledgement of bias by qualitative
researchers

5.  when the study fails to identify the validity problems
 when publicity about the research fails to incorporate
the researchers cautions

6.  selecting the most or least of anything
creates a regression effect

7.  selecting the lowest functioning mentally ill people to
study the effects of a therapy program
 selecting the poorest people to study the effects of an
anti-poverty program
 selecting chronic homeless to study the effects of a
housing program

8.  Study Dropouts may be the ones who needed
it most
 People also drop out when the program
works

9.  Occurs when researcher fails to control for the
effects of data collection and measurement
 using self report is often biased by social
desirability
 most clinical research is highly vulnerable to
measurement bias
 when the person perceives there is something to
lose by their answer

10. Differential Bias occurs when one group of study
participants is more likely to be misclassified than
the other
Misclassification of exposure is non-differential if
it is similar among cases and controls i.e. the
exposure (mis)classification is not related to the
person's disease status
Interviewer bias happens when interviewers ask
questions differently in case-control or cohort
studies
a histopathologist may be more likely to report on
a biopsy specimen as mesothelioma if a history of
asbestos exposure is reported (biased follow-up)
Salmonella cases may be more likely to remember

11.  Occurs when we administer the research
interview or questionnaire under adverse
conditions
 Poor layout, obligatory participation,
uncomfortable settings, etc…

12.  only cases within a limited range of a disease
spectrum are included.
 This more commonly occurs with more obvious
or advanced disease.
 For example, in a study investigating the ability
of MR imaging to depict cirrhosis, if only
advanced clinical cases are included the
sensitivity will be overestimated.

13.  occurs when individual preferences or local
practices determine which subjects undergo a
certain treatment or imaging study
 New treatments or imaging studies that have
not been universally accepted into clinical
practice are particularly prone to this type of
bias.

14.  Exists when study subjects are self-
selected for enrollment for treatment or
imaging
 Differences may exist between those who
volunteer and those who refuse participation
 Volunteers may be more health conscious or
even healthier than the general population

15.  may arise in studies in which subjects are
interviewed by an investigator who is also
involved in the interpretation of a test result
or determination of disease classification.
 The investigator may inadvertently “coach”
subjects or selectively review entire medical
records

16.  results when additional factors or
variables are associated with exposure
and disease status
 Common confounding variables are age and
sex
 Stratification (separation based on
variables) is a common method to address
confounding in the analysis phase

17.  journals tend to publish studies with positive
results or better-quality study designs
 does not arise within a given single study but
can be seen in a review and analysis of the
literature, as in a meta-analysis
 leads to overly optimistic results or inflated
associations

18.  retained knowledge of the results of one
study influences the interpretation of the
second study, potentially leading to a more
accurate reading or diagnosis
 learning-curve phenomenon

19.  study subjects are randomly allocated to
receive one or other of the alternative
treatments under study.
 Methods include allocation concealment and
blinding

20.  Allows for consideration of time factors
 i.e.: differences in patients who visit an
emergency room in the morning versus those
who visit during the night

21.  Information such as pertinent test results,
demographic data, or disease status, which
may affect an investigator's test
interpretation or assessment of an outcome,
is not available to the investigator
 A double-blinded study refers to one in
which both the investigator and study subject
are blinded to group assignment

22. Good
Intentions