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Types of Research Studies

Shahd AlAli

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Study Designs

Observational Analytic

Case control Cohort Cross-

sectional

Experimental

Clinical trail

Community trail

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Case-control Study • Observational & retrospective • Compare a group of people with disease to a

group without disease & look for prior exposure or risk factor.

• Usage of Odds ratio Patients with COPD had higher odds of history of smoking than whose without COPD

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Odds Ratio • Typically used in case-control studies.

100 patients with lung cancer and 100 patients without lung cancer were enrolled in a study. They were questioned about tobacco use over the past 20 years. 90 of lung cancer patients reporeted smoking as did 10 patients without lung cancer

Lung cancer No lung cancer

Smoking

Non-Smoking

90

10

10

90

90 x 90---------10 x 10

=8100-------100

81

If a person had lung cancer he is 81 times more likely to smoke

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Cohort Study • Compare a group with a given exposure to risk

factor to a group without such exposure. • Can be prospective or retrospective Who will develop the disease?/ Who developed the disease • Relative risk & attributable risk

Smokers had a higher risk of developing COPD than nonsmokers had

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Relative Risk • Used for cohort studies • Incidence rate of exposed group/incidence

rate unexposed It tells how much greater the chance does one group have of contracting the disease compared to other group?

A study enrolls 100 smokers and 100 nonsmokers. They are followed for 20 years for the development of lung cancer 30 of smokers and 10 from nonsmokers developed lung cancer

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Attributable Risk • The difference in risk between exposed and

unexposed groups Risk of lung cancer in smokers is 21% and risk in nonsmokers 1% THEN 20% of the 21% risk in smokers is attributed to smoking

Smokers 50:1000 – 2:1000= 48-1000. That is 48:1000 cases of lung cancer can be attributed to smoking

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Cross-sectional Study • Collects data from a group of people to asses

frequency of disease (& related risk factors) at particular point of time

• Measures disease prevalence • Can show risk factors association with disease,

but does not establish causality

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Observational studies Characteristic Case-Control

studies Cohort Studies Cross-Sectional

studies

Time Retrospective Prospective One time point Incidence NO YES NOPrevalence NO NO YES Role of disease Begin with

disease End with disease Prevalence of

disease Assesse Many risk factors

for single disease Single risk factor affecting many disease

Association of risk factors and disease

Data analysis Odds ratio to estimate risk

Relative risk & attributable risk to estimate risk

Chi-square to assesse association

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Clinical trail • Experimental study that compares therapeutic

benefits of 2 or more treatments, or treatment and placebo.