7.7 A researcher performs an experiment to determine if calcium supplements de-

Question

7.7 A researcher performs an experiment to determine if calcium supplements de- crease the probability of osteoporosis in lab mice. Seventy-four mice are assigned to the calcium treatment group and 226 are assigned to a control group. Osteoporosis Yes No 73 218 291 Calcium 74 No Calcium8 226 (a) The researcher tells you that a chi-square approximation cannot be used to approximate the two-tailed Fisher's exact test p-value because one of the cells of the above table is 1. Is this reasoning correct? Why or why not?

Explanation / Answer

Since for chi square approximation for the two tailed fisher exact test ,if df=1 then expected values must be greater than 5

here in our case expected values are

(74*9)/300 (74*291)/300

(226*9)/300 (226*291)/300

i.e.

2.22 71.78

6.78 219.22

Since EXpected value in cell 1 one equal to 2.22 which is less than 5 then we cannot use chi square approximation hence researcher reasoning is not exactly correct

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