PHP 405 Final Exam - Questions with Verified Answers

PHP 405 Final Exam - Questions with Verified Answers 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 ar ...

PHP 405 Final Exam - Questions with Verified Answers 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 is a type of selection bias that occurs in case-control studies when the controls do not accurately represent the exposure distribution in the source population that produced the cases. it occurs when different criteria were used to to select cases and controls State the main difference between differential and non differential misclassification, and state which directions each type of error can bias the study results -Nondifferential missclassification, inaccuracies that occur on one axis (exposure or disease) are independent from the other axis. of dichotomous variables biases the results towards the null -differential missclassification, inaccuracies that occur on one axis (exposure or disease) are dependent on the other axis. can bias the results either towards or away from the null State the different ways that each of the following biases can be minimized: A. Interviewer bias Mask interviewers to the study hypothesis and to the disease or exposure status of the study subjects, and carefully design the interview instrument B. Recall Bias mask study subjects to the study hypothesis, use diseased controls if conducting a case-control study, and carefully design an interview instrument C. selection bias ensure that selection of cases and controls is independent of exposure (in case-control study)and that selection of exposed and unexposed groups is independent of outcome (in retrospective cohort) and obtain high follow-up and participation rates (all studies) D. misclassification use the most accurate source of information, and use sensitive and specific criteria to define the exposure and disease Indicate whether the following statements are true or false: A. a study must be valid before its results can be generalized True B. Bias is introduced primarily during the analysis stage of a study False C. bias can pull an estimate of association either toward the null or away from the null True D. using an inaccurate case definition increases the likelihood of non-differential misclassification of the disease False E. including a large sample size reduces self-selection bias False F. poor recall and recall bias are synonymous terms for the same concept False Selection bias is most likely to occur in: A. case-control studies B. retrospective cohort studies C. experimental studies D. both retrospective and case-control E. both retrospective and experimental Recall bias is most likely to occur in: A. case-control studies B. prospective cohort studies C. experimental