Chris was interested in comparing the effects of two sunscreens (i.e. Ointment A

Question

Chris was interested in comparing the effects of two sunscreens (i.e. Ointment A and B) on reducing the degree of sunburn for 12~15 year-old boys. He decided to ask each boy to apply Ointment A to his left arm and Ointment B to his right arm. After applying ointments, each boy was asked to stay under the sun for an hour and was then measured the degree of burn for both arms on a 10-point scale with 10 being the worst burn and 1 being no burn at all. He randomly recruited 25 boys.

What parametric test would you use to compare the effects of two ointments?

a) Two-sample t test with unequal variances

b) Wilcoxon signed rank test

c) Paired t test Two-sample

d) Z test

Explanation / Answer

Here we compare two samples with n < 30 and standard deviation is unknown.

Therefore use " Two-sample t test with unequal variances".

Answer : (a) Two-sample t test with unequal variances.

Note: Wilcoxon test is non parametric test.

Paired t test is used when want to measure effect of some experiment.

Z test is used when n > 30 and standard deviation is known.

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