Question

1.Explain case-control and cohort study designs? How do the two designs differ? Give at least one example from the text or the literature. 2. Define validity and reliability using examples.

Answer 1

Cohort studies - In this design, a longitudinal approach is used to investigate the occurrence of a disease in existing pressured causes Merits - practically no bias cause - effect can be proved - Results generalisable Demerits - Takes more time - Expensive - Needs large sample - Looses to follow-up Example - A reseacher longitudinally observes the smoker for development of lung cancer Case Control Studies - In this design, cause of a disease are investigated after the occurence of a disease - Takes less time - Non - expensive - Rare diseases can be studied - Recall bias - Cause - effect can't be proved - Results not generalisable - Selecting suitable control - A researcher investigates history of smoking in patients diagnised with lung cancer Validity: - Accuracy of measurement: The degree to which an instrument measures that which is supposed to be measured Appropriate Meaningful Useful - validity coefficient rightarrow An estimate of the validity of a measure in the form of a correlation coefficient eg. A lest of intelligence should measure intelligence and not something else such as memory