Intermediate Epidemiology Review
2024/2025 Exam Questions and Answers
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Non-differential misclassification of exposure - 🧠ANSWER ✔✔Bias toward the
null
Non-differential misclassification of outcome (usually) - 🧠ANSWER ✔✔Bias
toward the null
Non-differential misclassification of outcome (sensitivity is misclassified- non-
perfect) - 🧠ANSWER ✔✔Then there will be no bias
Non-differential misclassification of exposure and outcome using odds ratio -
🧠ANSWER ✔✔Bias toward the null
Differential misclassification of exposure - 🧠ANSWER ✔✔Bias toward or away
from the null
over ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk difference is biased
toward the null
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,under ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk ratio is biased
toward the null
Both over and under ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk
ratio and risk difference biased toward the null
Sufficient cause model - 🧠ANSWER ✔✔Sufficient but not necessary
Necessary but not sufficient
Sufficient cause model and attributable risk - 🧠ANSWER ✔✔Of people who do
two things (i.e. smoke and drink), how much of their risk is attributable to just
one of the risks (i.e. just smoking). You look at overall risk for smoking (3 non-
drinking smokers have disease and 12 drinking-smokers have disease), that
means that 12 out of 15 of the cases came from drinking AND smoking together
(12/15), now there are 12 cases among drinking-smokers so (12/15) * number of
cases=12= ARF.
Special Exposure Cohort studies - 🧠ANSWER ✔✔People who were exposed to
something specific
General Population - 🧠ANSWER ✔✔Population "giving rise to the cases" is the
entire general population
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, Closed cohort - 🧠ANSWER ✔✔This is static. Exposure status is determined at the
beginning of the study and cannot be changed throughout. People are followed
overtime until they die, get disease, or are lost. They are not replaced, and thus
the population of the cohort will decrease over time and eventually run out.
You can directly calculate risks and incidence proportions.
Issues: what if people die, can we be sure they would not have gotten disease
had they lived longer? also, what if people get a disease more than once? if we
include them in our proportion it could be greater than 1.0, but if we don't then
we may underestimate the true burden of disease.
Open cohort - 🧠ANSWER ✔✔Dynamic. People enter in and out of study freely,
and new people can be accepted after study begins. Similarly, people's exposure
status can CHANGE over time.
For this reason, we can calculate incidence RATE.
Immortal person time - 🧠ANSWER ✔✔When a cohort study has inappropriately
been designed in a way that ensures that everyone will survive for a specific
period of time.
Usually come because one of the entry criteria into the study is dependent upon
survival.
Page 3 of 20
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER:
619652435. TERMS OF USE. PRIVACY STATEMENT. ALL RIGHTS RESERVED
2024/2025 Exam Questions and Answers
100% Guaranteed Success | Already
Rated A+
Non-differential misclassification of exposure - 🧠ANSWER ✔✔Bias toward the
null
Non-differential misclassification of outcome (usually) - 🧠ANSWER ✔✔Bias
toward the null
Non-differential misclassification of outcome (sensitivity is misclassified- non-
perfect) - 🧠ANSWER ✔✔Then there will be no bias
Non-differential misclassification of exposure and outcome using odds ratio -
🧠ANSWER ✔✔Bias toward the null
Differential misclassification of exposure - 🧠ANSWER ✔✔Bias toward or away
from the null
over ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk difference is biased
toward the null
Page 1 of 20
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER:
619652435. TERMS OF USE. PRIVACY STATEMENT. ALL RIGHTS RESERVED
,under ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk ratio is biased
toward the null
Both over and under ascertainment of cases in a cohort - 🧠ANSWER ✔✔Risk
ratio and risk difference biased toward the null
Sufficient cause model - 🧠ANSWER ✔✔Sufficient but not necessary
Necessary but not sufficient
Sufficient cause model and attributable risk - 🧠ANSWER ✔✔Of people who do
two things (i.e. smoke and drink), how much of their risk is attributable to just
one of the risks (i.e. just smoking). You look at overall risk for smoking (3 non-
drinking smokers have disease and 12 drinking-smokers have disease), that
means that 12 out of 15 of the cases came from drinking AND smoking together
(12/15), now there are 12 cases among drinking-smokers so (12/15) * number of
cases=12= ARF.
Special Exposure Cohort studies - 🧠ANSWER ✔✔People who were exposed to
something specific
General Population - 🧠ANSWER ✔✔Population "giving rise to the cases" is the
entire general population
Page 2 of 20
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER:
619652435. TERMS OF USE. PRIVACY STATEMENT. ALL RIGHTS RESERVED
, Closed cohort - 🧠ANSWER ✔✔This is static. Exposure status is determined at the
beginning of the study and cannot be changed throughout. People are followed
overtime until they die, get disease, or are lost. They are not replaced, and thus
the population of the cohort will decrease over time and eventually run out.
You can directly calculate risks and incidence proportions.
Issues: what if people die, can we be sure they would not have gotten disease
had they lived longer? also, what if people get a disease more than once? if we
include them in our proportion it could be greater than 1.0, but if we don't then
we may underestimate the true burden of disease.
Open cohort - 🧠ANSWER ✔✔Dynamic. People enter in and out of study freely,
and new people can be accepted after study begins. Similarly, people's exposure
status can CHANGE over time.
For this reason, we can calculate incidence RATE.
Immortal person time - 🧠ANSWER ✔✔When a cohort study has inappropriately
been designed in a way that ensures that everyone will survive for a specific
period of time.
Usually come because one of the entry criteria into the study is dependent upon
survival.
Page 3 of 20
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER:
619652435. TERMS OF USE. PRIVACY STATEMENT. ALL RIGHTS RESERVED
