PHP 405 Final Exam Questions With Answers Graded A+
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PHP 405 Final Exam Questions With Answers Graded A+
State the main similarity and main difference between cohort and experimental studies?
The main similarity is that both compare two or more exposure groups, which are followed to monitor outcome rates. The main difference is that the investigato...
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PHP 405 Final Exam Questions With Answers
Graded A+
State the main similarity and main difference between cohort and experimental studies?
The main similarity is that both compare two or more exposure groups, which are followed to
monitor outcome rates. The main difference is that the investigators allocate the exposure in
experimental studies, and the participants choose their exposure in cohort studies
describe the strengths and weaknesses of the three types of comparison groups used in cohort
studies. which one comes closes to the counterfactual ideal?
-Internal comparison: comes closest to the counterfactual ideal because it comes from the same
source population as the exposed group and so is most comparable. However, they are often hard to
identify
-General population: it is stable and easy to obtain. includes a lack of comparability to the exposed
group and lack of information on confounders.
-comparison cohort: least preferable option. although it may be comparable to the exposed group,
results from such a study are hard to interpret because the comparison cohort often has other
exposures.
State whether or not a cohort study is best suited for each of the following scenarios:
A. when little is known about a rare exposure
B. when little is known about a rare disease
C. when the study population will be difficult to follow up
D. when you want to learn about multiple effects of an exposure
A. Yes
B. No
C. No
D. Yes
why is it important to minimize loss to follow-up?
Loss to follow-up decreases the number of individuals who can be included in the analysis and so
reduces the statistical power of the study. also, if those who are lost have different rates of disease
than those who remain, the study results may be biased
how is person-time calculated within the context of a cohort study?
person-time is accrued for each individual in a cohort study. it begins when the follow-up period of
the study begins. it ends when one of the following occurs: the individual develops the outcome
under study, dies, is lost, or the follow-up period for the study ends
indicate whether the following statements are true or false:
a retrospective cohort study is more efficient than a prospective cohort study for studying diseases
with a long latent and induction period
true
cohort studies are the most sensible design for examining many exposures in relation to a single
disease
false
,the ideal comparison group for a cohort study would consist of exactly the same individuals in the
exposed group had they not be exposed
true
loss to follow-up can be a problem in a cohort study but not an experimental study
false
which of the following techniques that are commonly used in experimental studies can also be
applied to cohort studies?
A. Blinding
B. Placebo
C. randomization
D. Run-in period
A. Yes
B. No
C. No
D. No
Define each of the following terms:
A. TROHOC and TROHOC fallacy
TROHOC is the word cohort spelled backwards. Some epidemiologists use TROHOC as a disparaging
term for case-control studies because they believe that case-control studies are inferior to cohort
studies.
TROHOC fallacy means that it is incorrect to consider the logic of a case-control study backwards,
because the key comparison is identical to that of a cohort study.
B. odds ratio
-The odds of being a case among the exposed compared with the odds of being a case among the
nonexposed
-the odds of being exposed among the cases compared with the odds of being exposed among the
controls
C. case-crossover study
is a new variant of the case-control study that is used to study the acute effects of transient
exposures. Here, cases serve as their own controls, and the exposure frequency during a hazard
period is compared with that during a control period.
describe the situations in which it is desirable to conduct a case-control study
-when the exposure data is difficult or expensive to obtain, when the disease is rare, when the disease
has a long induction and latent period, when little is known about the disease, and when the
underlying population is dynamic.
describe one advantage and one disadvantage of using population controls in a case-control study
advantages: they usually come from the same source population as the cases and so they are likely to
be comparable.
disadvantages: they are time-consuming and expensive to identify, they are usually not as cooperative
as hospital controls, and their recall of prior exposures may not be as accurate as that of cases
, state the main advantages and disadvantages of case-control studies
advantages: case-control studies take less time and money to conduct than cohort and experimental
studies, they are well suited for studying rare diseases and diseases with long induction and latent
periods, and they can provide information on a large number of possible risk factors
disadvantages: the possibility of bias is increased, and it may be difficult to establish a correct
temporal relationship between the exposure and disease because the data are retrospective.
Indicate whether the following statements are true or false:
it is possible to obtain a valid estimate of disease prevalence from a typical case-control study
False
the purpose of a control group in a case-control study is to provide information on the disease
distribution in the source population that produced the cases
false
the control group in a case-control study should never include individuals who have the cases's
disease
false
a case-control study is the most efficient design for studying the health effects of rare exposures,
while a cohort study is the most efficient design for studying the risk factors for rare diseases
false
case identification is generally more difficult than control identification in case-control studies
false
the odds of illness are mathematically equivalent to the risk of illness
false
briefly define each of the following terms:
false
A. Recall Bias
occurs when the level of accuracy differs between the compared groups.
-in case-control study when cases remember or report their exposures differently from controls
-in cohort study when individuals who are exposed remember or report subsequent illnesses
differently than those who are unexposed
B. Healthy worker effect
occurs in occupational studies when disease and death rates in a working population are compared
with those among the general population.
C. control selection bias
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