5. You conduct a randomized controlled trial with vitamin B-12 and placebo and t

Question

5. You conduct a randomized controlled trial with vitamin B-12 and placebo and their effect on depressive symptoms. You randomly allocated in a double blind study to two groups recruiting from GPs. The difference in depressive symptoms between the two groups after 1 year of treatment was not statistically different but you find out that 30% of women were noncompliant with the vitamin B-12 tablets. If you omit them from the analysis the results of the study were significant. What analysis was done first and what was done second – what would you use and why? (4 points) 5. You conduct a randomized controlled trial with vitamin B-12 and placebo and their effect on depressive symptoms. You randomly allocated in a double blind study to two groups recruiting from GPs. The difference in depressive symptoms between the two groups after 1 year of treatment was not statistically different but you find out that 30% of women were noncompliant with the vitamin B-12 tablets. If you omit them from the analysis the results of the study were significant. What analysis was done first and what was done second – what would you use and why? (4 points) 5. You conduct a randomized controlled trial with vitamin B-12 and placebo and their effect on depressive symptoms. You randomly allocated in a double blind study to two groups recruiting from GPs. The difference in depressive symptoms between the two groups after 1 year of treatment was not statistically different but you find out that 30% of women were noncompliant with the vitamin B-12 tablets. If you omit them from the analysis the results of the study were significant. What analysis was done first and what was done second – what would you use and why? (4 points)

Explanation / Answer

In the first case, since the two groups (two samples) are independent of each other (since a double blind study was used, the patients were kept in the dark whether they are receiving a placebo or not), and the hypothesis test was to test the difference between their means of two independent samples, hence a Two-Sample t-test with a Pooled Variance method was used.

In the second case, 30% of women were non-complioant with the vitamin B-12 tablets and if we omit them from the anaslysis, the results become statistically significant. So this test captures the impact of gender on the test result. Hence,the second test performed was a Logistics Regression test.

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