Twenty-two volunteers at a cold research institute caught a cold after having been exposed to various cold viruses. A random selection of 10 of these volunteers was given tablets containing 1 gram of vitamin C. These tablets were taken four times a day.

The control group consisting of the other 12 volunteers was given placebo tablets that looked and tasted exactly the same as the vitamin C tablets. This was continued for each volunteer until a doctor, who did not know if the volunteer was receiving the vitamin C or the placebo tablets, decided that the volunteer was no longer suffering from the cold.

The length of time the cold lasted was then recorded.

At the end of this experiment, the following data resulted.

Do the data listed prove that taking 4 grams daily of vitamin C reduces the mean length of time a cold lasts? At what level of significance?

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Treated with Vitamin C Treated with Placebo 5.5 6.5 6.0 6.0 7.0 8.5 6.0 7.0 7.5 6.5 6.0 8.0 7.5 7.5 5.5 6.5 7.0 7.5 6.5 6.0 8.5 7.0