This is an example of a double blind experimental study investigating a therapeu

Question

This is an example of a double blind experimental study investigating a therapeutic value of vitamin C (ascorbic acid) for preventing common colds. The study was conducted during a 2-week period on a random sample of 279 college students. The contingency table below relating the variables incidence of common colds and taking or not taking vitamin C is shown here. 1 No Cold 109 Cold Total A. Fill in the missing cells in the table. Vitamin C Placebo Total B. How many college students who took vitamin C and still got a cold? 48 C Which variable makes most sense to use as the explanatory variable and which should be used as the response variable? D Determine the conditional percentages for students taking vitamin C and placebo. Write the percentages next to the counts in each box in the table. Did you find column % or row %? Explain briefly.

Explanation / Answer

from above:

a)

b)

number of college students who took vitamin C and still get a cold =15

c)

explanatory variable : having vitamin C or placebo

response variable: catching cold or not

d)

these are row percentages as they are taken against row marginal probablites of taking vitamin C or placebo

cold no cold total vitamin C 15 109 124 placebo 33 122 155 total 48 231 279

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