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#1
07-15-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,086 Times in 1,046 Posts Reputation: 2106
Testing for a statistical relationship

A study was performed on 200 elementary school students to investigate whether regular Vitamin A supplementation was effective in preventing colds during the month of March. 100 were randomized to receive daily Vitamin A supplements during the month of March, and 100 students were randomized to a placebo group (and did not receive Vitamin A) during the same month. The number of students getting at least one cold in March was computed in the two groups, and the results are given in the following 2 X 2 table.

........................Cold .........No Cold
Vitamin A ...........15 ............85.......... 100
Placebo .............25............ 75.......... 100
........................40............ 160......... 200

If you were interested in testing for a statistical relationship between taking Vitamin A and cold status in the population of elementary school students (ie: testing the null hypothesis of no difference in the proportion of colds in Vitamin A and placebo groups,versus the alternative of a difference in proportions), the correct statistical test is:
a. Two-sample t-test
b. Ad-hoc test for testing the equality of things
c. Chi-squared test
d. Paired t-test

#2
07-15-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 646 Threads: 52 Thanked 760 Times in 256 Posts Reputation: 771

c. Chi-squared test

 Tags Biostatistics-Epidemiology, Step-2-Questions

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