Hypothesis Testing


The health services of several countries are considering, or have recently introduced, screening programs for abdominal aortic aneurysm (AAA). An abdominal aortic aneurysm is a widening of the aorta (the main artery in the body) at the point where it passes down through the abdomen towards the pelvis. Because of the aneurysm, the wall of the aorta is weak and can rupture at any time, often resulting in sudden death. The larger the aneurysm becomes, the greater the risk of rupture. It is possible, however, to detect an AAA with an ultrasound scan of the abdomen. Once detected the aneurysm can be regularly monitored and, if necessary, surgically repaired. Supporters of screening believe that detection of AAA in the early stages with an ultrasound scan can prevent complications and deaths due to rupture of the aneurysm. Imagine that a screening program for AAA has been operating in your country for the past ten years and that the government has appointed you to conduct a study to determine its effectiveness. A randomized controlled trial has been ruled out, because it is considered unethical to randomize people to the control group. Outline the study you would conduct, assuming that AAA takes at least five years to develop, that detection in the early stages leads to a 80% ‘cure’ rate, and that approximately 60% of people aged 60 to 75 are regularly screened. Include the following points in your answer:

a.    The null hypothesis you want to test.
b.    The type of study design you would choose, and why it is the most appropriate design for determining the effectiveness of screening for AAA.
c.    Selection of subjects for your study.
d.    Measurement of exposure.
e.    The potential sources of bias and confounding, and the steps you would take to minimize them.
f.    How you would analyze your results.
g.    The potential weaknesses of your study design.


This question or case study belongs to statistics. The question is about a medical condition called abdominal aorta aneurysm which is the expansion of the abdominal aorta to about 50% of the normal size. Depending on the present prevalence of this condition, a hypothesis has been proposed that people 60% of the people between the ages of 60 to 75 are screened and that 80% of such cases can be cured. This hypothesis has to be tested with a sample group and available information. A deeper explanation has been given in the solution.

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