epidemiological study ( CASE CONTROL )

Question 1

what tyoe of study is case control study ?

Answer 1

an analytical retrospective study , where the cases are picked based on outcome along with a group of control , the exposure and outcome are both identified before the start of the study

Question 2

when is a case control study desirable ?

Answer 2

when the disease being studied is rare
when the study population is dynamic
when little is known about the risk factors for the disease

Question 3

what are cases for this type of study chosen based on ?

Answer 3

diagnostic criteria and eligibility criteria

Question 4

how are controls selected for a case control ?

Answer 4

1. by using multiple control groups from different sources
2. through matching
3. size of the control group should be similar to the cases

Question 5

what is meant by matching when it comes to choosing controls ?

Answer 5

controls should be similar to the cases in selected variables

Question 6

what is the limiting number of controls that can be used ?

Answer 6

using more than 3 controls for each case is not efficient

Question 7

what are the problems that arise with measuring exposure in case control studies ?

Answer 7

recall bias
interviewer bias
unlike cohort which is free from recall bias

Question 8

what is the most appropriate method to measure exposure to avoid any bias ?

Answer 8

using biological markers (an objective method)

Question 9

how can association be calculated form a case control study ?

Answer 9

using the odds ratio

Question 10

why cant relative risk be calculated to see the association inn a case control study ?

Answer 10

to calculate relative risk the incidence must first be calculated
incidence can only be deduced from a cohort study

Question 11

how is odds ratio calculated ?

Answer 11

ratio between the odds of exposure in cases and the odds of exposure in the controls

Question 12

what is the odds ratio a measure of ?

Answer 12

strength of the association between the risk factor and the outcome

Question 13

when can the odds ratio be an approximation of the relative risk ?

Answer 13

when prevalence of the disease in the general population is low
+
the risk ratio is low

Question 14

what are the disadvantages of case control studies ?

Answer 14

problems with bias
no time temporality like with cross sectional studies
( temporal association perserved in cohort studies)
selection of control group ay be difficult
odds ratio is only an estimation of the relative risk

Question 15

what are the sources of bias in case-control study ?

Answer 15

selection bias 
measurement bias 
recall bias 
observer bias
bias is reduced in cohort studies

Question 16

how does selection bias arise ?

Answer 16

maybe difficult to find appropriate controls

Question 17

how does measurement bias arise ?

Answer 17

through inaccuracy , reporting bias or recall bias