Case Control Study

Case Control Study

Q. 1

Recall bias is most commonly associated with which study design:

 A

Cohort study

 B

Case control study

 C

Cross-sectional study

 D

Randomized controlled trial

Q. 1

Recall bias is most commonly associated with which study design:

 A

Cohort study

 B

Case control study

 C

Cross-sectional study

 D

Randomized controlled trial

Ans. B

Explanation:

Case control study [Ref: Park 20/e p69]

  • Recall bias is associated with Case-control studies.
  • Park writes- “When cases and controls are asked questions about their past history, it may be more likely for the cases to recall the existence of certain events or factors than the controls who are healthy persons. For example, those who have had a myocardial infarction might be more likely to remember and recall certain habits or events than those who have not. Thus cases may have a different recall of past events than controls”
  • Recall bias is an error due to the differences in accuracy or completeness of recall to memory of past events or experiences. As a hypothetical example, suppose one is studying the possible relationship of congenital malformations to prenatal infections. A case-control study is conducted and interview is done of mothers of children with congenital malformations (cases) and mothers of children without malformations (controls). Each mother is questioned about infections she may have had during the pregnancy.
  • A mother who has had a child with a birth defect tries to identify some unusual event that occurred during her pregnancy with that child. She wants to know whether the abnormality was caused by something she did. Why did it happen? Such a mother may even recall an event, such as a mild respiratory infection, that a mother of a child without a birth defect may not even notice or may have forgotten completely. This type of bias is known as recall bias.
  • Bias is said to have occurred when there is a systematic difference between the results from a study and the true state of affairs. Bias may be introduced at all stages of the research process, from study design, through to analysis and publication. Bias can create a spurious association (i.e. overestimation of an effect) or mask a real one (underestimation of an effect). While appropriate statistical methods can reduce the effect of bias, they may not be able to eliminate it entirely. Innumerable number of bias have been listed.
  • Bias associated with cohort study:
  1. Selection
  2. Confounding
  3. Interviewer’s bias
  • Bias associated with Case-control study:
  1. Selection
  2. Confounding
  3. Recall bias
  4. Berkesonian bias
  5. Interviewer’s bias
  • Interviewer bias is a type of information bias that arises when an interviewer consciously or unconsciously elicits inaccurate information from study subjects. Interviewer bias can result in differential error, which can seriously distort disease-exposure associations, if the interviewer is aware of the disease status and exposure hypothesis in a case-control study, or if the interviewer is aware of the exposure status and outcome hypothesis in a cohort study. In the former case, the interviewer may probe more deeply for evidence of exposure among cases than among controls. In the latter case, the interviewer may try to elicit evidence of health effects more assiduously in exposed than in unexposed cohort members.
  • Selection bias occurs when patients included in the study are not representative of the population to which the results will be applied.
  • Confounding bias occurs when we find a spurious association between a potential risk factor and a disease outcome or miss a real association between them because we have failed to adjust for any confounding variables. A confounding variable or confounder is an exposure variable that is related to both the outcome variable (e.g. disease) and to one or more of the other exposure variables. For example in the study of the role of alcohol in the etiology of esophageal cancer, smoking is the confounding factor because it is associated with the consumption of alcohol and it is also an independent risk factor for esophageal cancer. Thus the effects of alcohol consumption on esophageal cancer can only be determined when the influence of smoking is neutralized by matching.
  • Berkesonian bias: It occurs when patient admission rates vary between the experimental and control groups, especially in studies that use hospitalized patients for both groups. For example, this type of bias is present when hospitalized patients with the risk factor (experimental group) are admitted at a higher rate than the control group.

Q. 2

Nested case control study is a type of:

 A

Retrospective study

 B

Prospective study

 C

Descriptive study

 D

Cross-sectional study

Q. 2

Nested case control study is a type of:

 A

Retrospective study

 B

Prospective study

 C

Descriptive study

 D

Cross-sectional study

Ans. B

Explanation:

Prospective study [Ref: Epidemiology and prevention: a systems-based approach By John Yarnell p25,261

Lets see various analytical studies:

We already know about the typical case control study and the cohort study.

A case control study begins with the cases, i.e. diseased subjects, and the controls, i.e. non-diseased subjects, and then investigates their exposure status.

A cohort study begins with exposed and non-exposed groups and then studies the occurrence of the disease. A typical case control study is retrospective and typical cohort study is prospective in design.

[Retrospective study is one that looks backward in time, usually using medical records and interviews with patients who already known to have a disease.

Prospective study is a study in which the subjects are identified and then followed forward in time.] Now let’s see other types of analytical studies:

Retrospective cohort study?

  • In these, the exposure status of a whole cohort (for example an occupational cohort) is accurately known from historical or occupational records, and the disease status of individuals from the whole cohort is obtained in current time. Such studies are relatively quick and inexpensive to conduct.
  • The design of a retrospective cohort study differs from that of a prospective one in that the assembly of the cohort, baseline measurements, and follow-up have all happened in the past. This type of study is only possible if adequate data about the risk factors and outcomes are available on cohort of subjects that has been assembled for other purposes.
  • In a retrospective cohort study, a cohort is assembled by reviewing records to identify exposures in the past. Based on the recorded exposure histories, cohort members are divided into exposed and nonexposed groups, or according to level of exposure. The investigator then reconstructs health experience subsequent to exposure, up to some defined point in the more recent past or up to the present time.
  • Retrospective cohort studies have many of the advantages of prospective cohort studies but can be completed much more quickly and often with less expense. However, retrospective cohort studies depend on the availability of accurate information on past exposures.

Nested case control (also k/a Prospective case-control study)

  • A nested case-control study is a case control study “nested” within a cohort study.
  • Nested case control study is done when assessment of exposure, or one aspect of exposure, may be very time-consuming and costly and instead of undertaking measurement on everyone in a cohort, it may be more prudent to wait to determine which subjects in a cohort develop the disease under study (i.e. the cases for the nested case-control study). Thereafter, a control group of subjects could be selected amongst those from the original cohort who had not developed the disease.
  • For example: Suppose that an investigator is interested in whether serum beta carotene affects the risk of colon cancer. In a traditional prospective cohort study, beta carotene levels would be measured in blood samples from all the cohort members, and subsequent disease incidence would be determined according to the level of beta carotene. In a nested case-control study, blood samples from all of the (say, 10000) cohort members would be frozen and stored without measuring beta carotene. Suppose that after 10 years, 200 cohort members had been diagnosed with colon cancer and 9,800 are free of colon cancer. All of the cases and a sample of, for example, 400 controls without the disease could be selected and beta carotene could be measured in the stored serum. The cases and controls could then be compared according to beta carotene level, as in a traditional case-control study. Controls are usually selected from unaffected cohort members who are still alive and under surveillance at the time the cases developed the disease. This greatly reduces the cost compared with measurement of beta carotene levels of all 10,000 cohort members but assures that beta carotene measures represent levels before the diagnosis of the disease.
  • These studies are termed ‘nested’ because the exposure status is created and ascertained at the baseline examination (and subsequently ‘incubated’ until the end points are evaluated).
  • Compared with case-control studies, nested case-control studies can reduce ‘recall bias’ and temporal ambiguity, and compared with cohort studies can reduce cost and save time.
  • The drawback of nested case-control studies is non-diseased persons from whom the controls are selected may not be fully representative of the original cohort, due to death or failure to follow-up cases.

The nested case-cohort study

  • The nested case-cohort approach is the same design as nested case-control study except that the controls are a random sample of all the members of the cohort regardless of outcomes. This means that there will be some cases among those sampled for the comparison group, who will also appear among the cases and be analyzed as such (removing them from the cohort sample for purposes of analysis is a negligible problem provided that the outcome is uncommon). This approach has the advantage that the controls represent the cohort in general, and therefore provide a basis for estimating incidence and prevalence in the population form which it was drawn. More important, it means that this cohort sample can be used as the comparison group for more than one type of outcome provided that it is not too common.
  • Nested case-control and case-cohort studies are especially useful for costly measurements on serum, electronic images, hospital charts, etc. that have been archived at the beginning of the study and preserved for later analysis. In addition to the cost saving of not making the measurements on the entire cohort, the design allows the investigator to introduce novel measurements that were not available at the outset of the study. The design preserves all the advantages of cohort studies that result from collecting predictor variables before the outcomes have happened, and it avoids the potential biases of conventional case-control studies that drain cases and controls from different populations and cannot make measurements on cases and control who have died.
  • The chief disadvantage of this design is that many research questions and circumstance are not amenable to the strategy of storing materials for later analysis on a sample of the study subjects.
  • Prospective study is a design in which the subjects are identified and then followed forward in time. A prospective study watches for outcomes, such as the development of a disease, during the study period and relates this to other factors such as suspected risk or protection factor(s). Thus we can see that the nested case-control is a prospective study.

Q. 3 Recall bias is most commonly asso­ciated with which study design:
 A Case control study
 B Cohort study
 C Cohort case control study
 D Cross sectional study
Q. 3 Recall bias is most commonly asso­ciated with which study design:
 A Case control study
 B Cohort study
 C Cohort case control study
 D Cross sectional study
Ans. A

Explanation:

Case control study


Q. 4

All of the following statements regarding case control study are true, except

 A

Used to find the relative risk

 B

Odds ratio can be calculated

 C

Relatively cheap

 D

Used for rare diseases

Q. 4

All of the following statements regarding case control study are true, except

 A

Used to find the relative risk

 B

Odds ratio can be calculated

 C

Relatively cheap

 D

Used for rare diseases

Ans. A

Explanation:

Using case control study only odds ratio can be calculated.

Incidence rates, relative risk and attributable risk can be calculated using cohort study. Case control study is inexpensive, easy to carry out, used to investigate rare diseases, used to identify risk factors, allows study of different etiological factors and is associated with minimal ethical problems.


Reference:
Parks Textbook of Preventive And Social Medicine 20th edition, page 70.


Q. 5

Which of the following statement is not correct regarding case control study?

 A

Proceeds from effect to cause

 B

Exposure already occurred

 C

Odd’s ratio can be determined

 D

Incidence rate can be calculated

Q. 5

Which of the following statement is not correct regarding case control study?

 A

Proceeds from effect to cause

 B

Exposure already occurred

 C

Odd’s ratio can be determined

 D

Incidence rate can be calculated

Ans. D

Explanation:

Case control study generally yields estimate of RR (Odd’s ratio) only.

Cohort study yields incidence rate, RR as well as AR.

Case control study proceeds from the effect to cause.

It starts with the disease.

Ref: Park, 20th Edition, Page 69

Q. 6

In a case control study on smoking and lung cancer, out of 35 lung cancer patients, 33 are smokers. Out of 82 controls, 27 are non smokers. Find the odds ratio:

 A

0.21

 B

8.1

 C

4.1

 D

2.1

Q. 6

In a case control study on smoking and lung cancer, out of 35 lung cancer patients, 33 are smokers. Out of 82 controls, 27 are non smokers. Find the odds ratio:

 A

0.21

 B

8.1

 C

4.1

 D

2.1

Ans. B

Explanation:

    Cancer   Controls without cancer
  Smokers   33 (a)   55 (b)
  Non smokers   2 (c)   27 (d)
  Total   35   82

Odds ratio=  a×d/b×c  = 33×27/55×2= 8.1

REMEMBER: while constructing table keep exposure in rows (e.g.: smokers v/s non smokers here) and presence or absence of disease condition in columns (e.g.: cancer v/s no cancer)         

Ref: Park’s textbook of Preventive and Social Medicine, 21stedition, page-69.


Q. 7

True about case control study A/E

 A

Less expensive

 B

Those with disease and not diseased compared

 C

Attributable risk is estimated

 D

None of these

Q. 7

True about case control study A/E

 A

Less expensive

 B

Those with disease and not diseased compared

 C

Attributable risk is estimated

 D

None of these

Ans. C

Explanation:

Case control study:
  • An epidemiological study where a group of individuals with disease (CASE) are compared with a group of individuals who are not suffering from disease (CONTROLS) in terms of specific disease causing exposures. 
  • Since the starting point is a group of people who already have suffered from the disease, this is labeled as a retrospective study.(BACKWARD LOOKING STUDY)
Advantages of case control studies
  • Relatively quick and easy to undertake.
  • Relatively cheap to undertake.
  • Only method useful in rare diseases.
  • Not enmeshed in problems of follow-up as the data is collected at one point in time.
  • Can be used to study the effect of many exposure variables on a single disease outcome.
Drawbacks of case control studies
  • Prone to selection and recall bias.
  • Can’t measure relative risk or provide incidence estimates . (Only odd’s ratio can be calculated from the type of study, which is a rough estimate of relative risk. But when the disease in question is a rare one odd’s ratio is almost equal to relative risk.)
  • Sometimes the occurrence of the exposure in terms of time, i.e. whether it occurred before the disease may be difficult to estimate.
  • Can’t be used for rare exposures.
Attributable risk can be estimated in a cohort study.
 
Ref : Park’s Textbook of Preventive and Social Medicine; 18th edition; Page-65

Q. 8

All of the following are true about case control study except-

 A

Rapid and inexpensive

 B

No risk to subjects

 C

Risk factor can be identified

 D

Less prone to bias

Q. 8

All of the following are true about case control study except-

 A

Rapid and inexpensive

 B

No risk to subjects

 C

Risk factor can be identified

 D

Less prone to bias

Ans. D

Explanation:

Ans. is ‘d’ i.e., Less prone to bias 

  1. Case control study

o Case control study is a common first approach to test causal hypothesis.

  • Case              —>             Case is an individual who has developed the disease.
  • Control            —>       Is an individual who has not developed the disease but is otherwise comparable to case (e.g. age, sex, occupation, social status etc).

o The case – control study has three distinct features ‑

i)     Both exposure (risk factor) and outcome (disease) have occurred before the start of study so, there is no further risk for subjects.

ii) Study proceeds backwards from effect to cause —-> retrospective study.

iii) It uses a control or comparison group to support or refute an inference.

o The focus is on a disease that has already developed.

o Association between risk factor and disease can be tested —> risk factor can be identified.

o For example, if it is our intention to test the hypothesis that cigarette smoking causes lung cancer, the investigation begins by assembling a group of lung cancer cases (a + b) and a group of suitable matched control (not having lung cancer). Then past history for the presence or absence of smoking is explored in both groups. Suspected risk factor      

o If the frequency of smoking, a / (a + c) is higher in cases than in control b / (b + d), an association is said to exist between smoking and lung cancer.

o Case – control study is rapid and inexpensive.

o Problem of bias is common.


Q. 9

In a case control study, the most characteristic feature is –

 A

Odds ratio estimation 

 B

Problem bias

 C

Yield incidence rate

 D

Expensive

Q. 9

In a case control study, the most characteristic feature is –

 A

Odds ratio estimation 

 B

Problem bias

 C

Yield incidence rate

 D

Expensive

Ans. A

Explanation:

Ans. is ‘a’ i.e., Odds ratio estimation 

o Final step in case control study is analysis to find out ‑

i)    Exposure rates among cases and controls to suspected factor.

ii)  Estimation of disease risk associated with exposure (odds ratio).

i)         Exposure rates

o A case control study provides a direct estimation of the exposure rates (frequency of exposure) to a suspected factor.

ii)         Odds – ratio (cross product ratio)

o From a case control study odds ratio can be derived which a measure of the strength of association between risk factor and outcome.

o Odds ratio is closely related to relative risk (which is analysed in cohort study) —> odds ratio represents only an estimate of relative risk.

o The odds ratio is cross product of entries in above table

o Odds ratio is a key parameter in analysis of case control studies.

Why is it not possible to estimate relative risk in case-control study ‑

o Relative risk is the ratio between the incidence of disease among exposed and incidence among non-exposed. o So, for relative risk estimation, incidence rate is required.

o But incidence rate can not be calculated by case control study as there is no denominator (poulation at risk).

o Because both disease and exposure have already occured, there is no risk for the subjects in the study —> There is no population at risk.


Q. 10

In case control study, the risk is calculated by‑

 A

Relative risk

 B

Attributable risk

 C

Cross product ratio

 D

None

Q. 10

In case control study, the risk is calculated by‑

 A

Relative risk

 B

Attributable risk

 C

Cross product ratio

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Cross product ratio 

o Risk in case control study is calculated by odds ratio (cross product ratio).


Q. 11

In a case controlled study. It is found that the disease is more common in the group taking coffee as compared to the control group. The significance of this is –

 A

Cause and effect relationship established

 B

Disease median can be calculated

 C

Caffeine is associated with occurrence of disease

 D

Controls will not get the disease

Q. 11

In a case controlled study. It is found that the disease is more common in the group taking coffee as compared to the control group. The significance of this is –

 A

Cause and effect relationship established

 B

Disease median can be calculated

 C

Caffeine is associated with occurrence of disease

 D

Controls will not get the disease

Ans. C

Explanation:

Ans. is ‘c’ i.e., Caffeine is associated with occurrence of disease 

Case-control study does not establish the cause and effect relationship because it can not distinguish between cause and associated factors.

o Case-control study can only tell the association between cause and effect.


Q. 12

In case control study of buccal carcinoma ‑

 A

CA is commoner in zarda pan users than non users

 B

Zarda pan is a cause of buccal CA

 C

Zarda pan is associated with buccal CA

 D

If use of zarda pan is stopped, number of cases will reduce

Q. 12

In case control study of buccal carcinoma ‑

 A

CA is commoner in zarda pan users than non users

 B

Zarda pan is a cause of buccal CA

 C

Zarda pan is associated with buccal CA

 D

If use of zarda pan is stopped, number of cases will reduce

Ans. C

Explanation:

Ans. is ‘c’ i.e., Zarda pan is associased with buccal CA 


Q. 13

All of the following are characteristics of case control study except –

 A

Quick results are obtained

 B

Measures incidence rate

 C

Proceeds from effect to cause

 D

Inexpensive study

Q. 13

All of the following are characteristics of case control study except –

 A

Quick results are obtained

 B

Measures incidence rate

 C

Proceeds from effect to cause

 D

Inexpensive study

Ans. B

Explanation:

Ans. is ‘b’ i.e., Measures incidence rate 

o Incidence rate can not be measured by case-control study as denominator (population at risk is not available).


Q. 14

Which of the following statement is correct in regards to case control study –

 A

Proceeds from effect to cause

 B

Exposure already occured

 C

Odd’s rad ratio can be determined

 D

All of the above

Q. 14

Which of the following statement is correct in regards to case control study –

 A

Proceeds from effect to cause

 B

Exposure already occured

 C

Odd’s rad ratio can be determined

 D

All of the above

Ans. D

Explanation:

Ans. is ‘a’ i.e., Proceeds from effect to cause; ‘b’ i.e., Exposure already occured & `c’ i.e., Odd’s rad ratio can be determined

o Case-control study proceeds from effect to cause, i.e. exposure to risk factor has already occured.

o Odd’s ratio is estimated by case control study.


Q. 15

True about case control study –

 A

Less expensive

 B

Those with disease and not diseased compared

 C

Attributable risk is estimated

 D

None of these

Q. 15

True about case control study –

 A

Less expensive

 B

Those with disease and not diseased compared

 C

Attributable risk is estimated

 D

None of these

Ans. A

Explanation:

Ans. is ‘a’ i.e., Less expensive 


Q. 16

Case control study, All can be measured except – 

 A

Relative risk

 B

Incidence 

 C

Odds ratio

 D

a and b both

Q. 16

Case control study, All can be measured except – 

 A

Relative risk

 B

Incidence 

 C

Odds ratio

 D

a and b both

Ans. D

Explanation:

Ans. is ‘a’ i.e., Relative risk; ‘b’ i.e., Incidence

o Relative risk & Incidence cannot be measured in case-control study as there is no denominator population at risk.

o Cause and effect relationship cannot be established in case – control study because it can not distinguish between cause and associated factors.

o Case – control study can only tell the association between cause and effect.


Q. 17

Cohort study is better than case control study in all ways except – 

 A

Greater comparability 

 B

Lesser time spent

 C

Prospective analysis

 D

Less Bias

Q. 17

Cohort study is better than case control study in all ways except – 

 A

Greater comparability 

 B

Lesser time spent

 C

Prospective analysis

 D

Less Bias

Ans. B

Explanation:

Ans. is ‘b’ i.e., Lesser time spent 

o Cohort study is more time consuming.

o Cohort study is prospective study.

o Chances of bias are high in case-control study.


Q. 18

All of following are advantages of case control study except –

 A

Cheaper

 B

Less time consuming

 C

Possible to study many diseases

 D

All

Q. 18

All of following are advantages of case control study except –

 A

Cheaper

 B

Less time consuming

 C

Possible to study many diseases

 D

All

Ans. C

Explanation:

Ans. is ‘c’ i.e., Possible to study many diseases 

o Many risk factors can be studied (not many diseases).

o Case – control study has more chances of bias in comparison to Cohort study.


Q. 19

Direction of case control study‑

 A

Direction of study is reverse but time is forward

 B

Direction of study is forward and time is also forward

 C

Direction of study is forward and time is reverse

 D

Direction of study is reverse and time is also reverse

Q. 19

Direction of case control study‑

 A

Direction of study is reverse but time is forward

 B

Direction of study is forward and time is also forward

 C

Direction of study is forward and time is reverse

 D

Direction of study is reverse and time is also reverse

Ans. A

Explanation:

Ans. is ‘a’ i.e., Direction of study is reverse but time is forward 

o In case control study

i) Direction of study Reverse

Time Forward o In cohort study

i)            Direction of study —> Forward

ii)           Time -Forward


Q. 20

As compared to a routine case control study, nested case control study avoids problems (in study design) related to –

 A

Temporal association

 B

Confounding bias

 C

Need for long follow up

 D

Randomization

Q. 20

As compared to a routine case control study, nested case control study avoids problems (in study design) related to –

 A

Temporal association

 B

Confounding bias

 C

Need for long follow up

 D

Randomization

Ans. A

Explanation:

Ans. is ‘a’ i.e., Temporal association 

Nested case control study

  • It is hybrid study in which a case control study is nested in a Cohort study.
  • In this study a cohort is selected and data about exposure is obtained from interviews and/or biospcimens tests. o Cohort is then followed up for a period of time.

o The investigator identifies cases of disease that occured in the Cohort during follow up and disease free individuals within the Cohort that serve as control.

  • Using previously collected data (i.e., History taken at the start of study and biospecimens) the examinar compares the exposure frequencies in cases and controls as in non-nested case-control study.

Following flow charts will help you to understand the difference in different study.

Case control Vs Nested case control study

o In case control study, cases and controls are selected at the start of study and then the data about exposure in both group is obtained.

o In nested case control study, cases and controls are developed during follow up. Exposure frequencies are compared by the data collected at the start of study.

Cohort Vs nested case control study

o In cohort study, study cohort (exposed to risk factor) and control Cohort (not exposed to risk factors) are selected at the start of study and then these groups are followed for the development of disease.

o In nested case control study, data about exposure is obtained at the start of study in a single cohort and then it is followed for the development of disease. Once the cases and controls are identified during follow up, the exposure in cases and controls are compared by using data, collected at the start of study.

Advantages of nested case control study

Nested studies,

1) Can utilize the exposure and confounder data originally collected before the onset of the disease, thus reducing potential recall bias and temporal ambiguity,

and

2)Include cases and controls drawn from the same cohort, therefore decreasing the likelihood of selection bias. The nested case-control study is thus considered a strong observational study, comparable to its parent cohort study in the likelihood of an unbiased association between an exposure and outcome.

A concern, usually minor, is that the remaining nondiseased persons from whom the controls are selected when it is decided to do the nested study, may not be fully representative of the original cohort due to death or losses to follow-up.


Q. 21

Nested case control study is a type Of-

 A

Retrospective study

 B

Prospective study

 C

Descriptive study

 D

Cross sectional study

Q. 21

Nested case control study is a type Of-

 A

Retrospective study

 B

Prospective study

 C

Descriptive study

 D

Cross sectional study

Ans. B

Explanation:

Ans. is ‘b’ i.e., Prospective study 

Nested case control study is also known as prospective case-control study.


Q. 22

Problem of bias is maximum with –

 A

Cohort study

 B

Case study

 C

Case control study

 D

Experimental study

Q. 22

Problem of bias is maximum with –

 A

Cohort study

 B

Case study

 C

Case control study

 D

Experimental study

Ans. C

Explanation:

Ans. is ‘c’ i.e., Case control study 


Q. 23

Causal association factors can be revealed by ‑

 A

Case control study

 B

Cohort study

 C

Cross sectional study

 D

Experimental study

Q. 23

Causal association factors can be revealed by ‑

 A

Case control study

 B

Cohort study

 C

Cross sectional study

 D

Experimental study

Ans. A

Explanation:

Ans. is ‘a’ i.e., Case Control study 

o In a case control study we proceed from the effect to cause therefore we can study many causal associated factors at a time.

o Whereas in cohort study we proceed from the cause to effect, therefore we can get to several diseases associated with the cause but we can not study many causal factors at a time.


Q. 24

Recall bias is most commonly associated with which study design –

 A

Case control study

 B

Cohort study

 C

Cohort case control study

 D

Cross-sectional study

Q. 24

Recall bias is most commonly associated with which study design –

 A

Case control study

 B

Cohort study

 C

Cohort case control study

 D

Cross-sectional study

Ans. A

Explanation:

Ans. is ‘a’ i.e., Case control Study 

Recall bias (Memory bias) :

o This type of bias may occur when cases and controls are asked to recall certain events, and subjects in one group are more likely to remember the event than those in the other group.

o For example people take aspirin commonly and for many reasons, but patients diagnosed as having peptic ulcer disease may recall the ingestion of aspirin in greater accuracy than those without G1 problems. Also patients who have had an MI are more likely to recall and remember certain habits (like eating habit) with greater accuracy than those who have not had an MI.


Q. 25

Case control study is used for study of – 

 A

Common diseases

 B

Uncommon diseases

 C

Rare diseases

 D

Unkown diseases

Q. 25

Case control study is used for study of – 

 A

Common diseases

 B

Uncommon diseases

 C

Rare diseases

 D

Unkown diseases

Ans. C

Explanation:

Ans. is ‘c’ i.e., Rare diseases 


Q. 26

Case control study is –

 A

Prospective

 B

Retrospective

 C

Cross sectional

 D

None of the above

Q. 26

Case control study is –

 A

Prospective

 B

Retrospective

 C

Cross sectional

 D

None of the above

Ans. B

Explanation:

Ans. is ‘b’ i.e., Retrospective 


Q. 27

A case control study is not characterized by ‑

 A

Cases with the disease are compared to controls without the disease

 B

Assessment of past exposure may be biased

 C

Definition of cases may be difficult

 D

Incidence rates may be computed directly

Q. 27

A case control study is not characterized by ‑

 A

Cases with the disease are compared to controls without the disease

 B

Assessment of past exposure may be biased

 C

Definition of cases may be difficult

 D

Incidence rates may be computed directly

Ans. D

Explanation:

Ans. is ‘d’ i.e., Incidence rates may be computed directly


Q. 28

Case control study – estimate –

 A

Only odd’s ratio

 B

Odds ratio and attributable risk

 C

Relative risk, attributable risk, population attributable risk

 D

Incidence, Relative risk, and attributable risk

Q. 28

Case control study – estimate –

 A

Only odd’s ratio

 B

Odds ratio and attributable risk

 C

Relative risk, attributable risk, population attributable risk

 D

Incidence, Relative risk, and attributable risk

Ans. A

Explanation:

Ans. is ‘a’ i.e., Only odd’s ratio 


Q. 29

The association between disease & risk factor in a case control study is studied by – 

 A

Relative role

 B

Attributable role

 C

Population attributable role

 D

Odds ratio

Q. 29

The association between disease & risk factor in a case control study is studied by – 

 A

Relative role

 B

Attributable role

 C

Population attributable role

 D

Odds ratio

Ans. D

Explanation:

Ans. is ‘d’ i.e., Odds ratio


Q. 30

What does the limbic systeminclude?

 A
 B
 C
 D
Q. 30

What does the limbic systeminclude?

 A
 B
 C
 D
Ans.

Explanation:

Hyppocampus and amygdala


Q. 31

All of the following are true about case control study except ‑

 A

Rapid and inexpensive

 B

No risk to subjects

 C

Risk factor can be identified

 D

Less prone to bias

Q. 31

All of the following are true about case control study except ‑

 A

Rapid and inexpensive

 B

No risk to subjects

 C

Risk factor can be identified

 D

Less prone to bias

Ans. D

Explanation:

Ans. is ‘d’ i.e., Less prone to bias


Q. 32

Case control study is an example of ‑

 A

Prospective study

 B

Retrospective study

 C

Combined retrospective and prospective study

 D

Study at one point of time

Q. 32

Case control study is an example of ‑

 A

Prospective study

 B

Retrospective study

 C

Combined retrospective and prospective study

 D

Study at one point of time

Ans. B

Explanation:

Ans. is ‘b’ i.e., Retrospective study


Q. 33

Example of case control study (risk factor and disease/outcome) ‑

 A

Maternal smoking and congenital malformation

 B

Vaginal adenocarcinoma and intrauterine exposure to DES

 C

Thalidomide exposure and teratogenicity

 D

All of the above

Q. 33

Example of case control study (risk factor and disease/outcome) ‑

 A

Maternal smoking and congenital malformation

 B

Vaginal adenocarcinoma and intrauterine exposure to DES

 C

Thalidomide exposure and teratogenicity

 D

All of the above

Ans. D

Explanation:

Ans. is `d’ i.e., All of the above

Important risk factors and their outcomes/diseases which have been studied by case-control study are :-

  1. Cigarette smoking and lung cancer.
  2. Maternal smoking and congenital malformation.
  3. Radiation and leukemia.
  4. OCP used and hepatocellular carcinoma.
  5. Herpes-simplex and Bells palsy.
  6. Artificial sweeteners and bladder cancer.
  7. DES exposure in fetal life and vaginal adenocarcinoma.
  8. OCP use and thromboembolic disease.
  9. Thalidomide use in pregnancy and teratogenicity.

Q. 34

Matching is method to eliminate confounding bias. It is used in‑

 A

Case control study 

 B

Cohort study

 C

Experimental study 

 D

Cross sectional study

Q. 34

Matching is method to eliminate confounding bias. It is used in‑

 A

Case control study 

 B

Cohort study

 C

Experimental study 

 D

Cross sectional study

Ans. A

Explanation:

Ans. is ‘a’ i.e., Case control study 

  • Matching is most useful in case control studies (though it can also be used in cohort studies, but benefit is not assured if exposure is not randomized).

Method Used to Control Confounding

Method Utility to control confounding
Randomization 

Most ideal method

Restriction  Limiting study to people who have particular characteristics 
Matching  Mostly useful in case control studies
Stratification 

Useful for larger studies

Statistical modeling

When many confounding variables exist simultaneously




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