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	15	109	124
Placebo	33	122	155
Total	48	231	279

Complete parts (b, c, d).

2(b) Which variable makes most sense to use as the explanatory variable and which should be used as the response variable?

Cold is [ Select ]

[-"the response variable",

-"the explanatory variable",

-"not a variable"]

Health condition is [ Select ]

[-"the explanatory variable",

-"the response variable",

-"not a variable"]

Placebo is [ Select ]

[-"the response variable",

-"the explanatory variable",

-"not a variable"]

Treatment is [ Select ]

[-"not a variable",

-"the response variable",

-"the explanatory variable"]

Vitamin C is [ Select ]

[-"not a variable",

-"the explanatory variable",

-"the response variable"]

2(c) Determine the conditional percentages for students taking vitamin C and placebo.

Did you find column percentages or row percentages? The answer: found percentages.

Round percentages to integers as needed.

	Cold	No cold
Vitamin C	%	%
Placebo	%	%

2(d) Summarize what you can say about how taking vitamin C and preventing a common cold.