The nutritionist and medical doctors have always believed that Vitamin C is highly
effective in reducing the incidents of colds. To test this belief, a random sample of 13
persons is selected and they are given daily doses of Vitamin C under medical supervision
over a one-year period. The number of codes each person catches during the year is
recorded and a comparison is made with the number of colds contracted by each such
person during the previous year. This comparison is tabulated as follows, along with the
sign of the change.
Observation 1 2 3 4 5 6 7 8 9 10 11 12 13
Without
Vitamin C
7 5 2 3 8 2 4 4 3 7 6 2 10
With
Vitamin C
2 1 0 1 3 2 3 5 1 4 4 3 4
Use the sign test at 0.05 level of significance, determine if Vitamin C is effective in reducing
colds.
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