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.

Cold No Cold Total

Vitamin C 109

Placebo 33

Total 48

A. Fill in the missing cells in the table.

B. How many college students took vitamin C and still got

a cold?

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 the placebo. Write the percentages next to the

counts in each box in the table. Did you find column % or row %? Explain briefly.

E Summarize what you can say about the relationship between taking vitamin C and preventing a common cold. Write

complete sentences. Make sure to use the correct % to support your answer.