An antihistamine is frequently studied using a model to examine its effectiveness (compared to a placebo) in inhibiting a positive skin reaction to a known allergen. Consider the following situation. Individuals are screened to find 20 subjects who demonstrate sensitivity to the allergen to be used in the study. The 20 subjects are then randomly assigned to one of two treatment groups (the known antihistamine and an identical- appearing placebo), with 10 subjects per group. At the start of the study, a baseline (predrug) sensitivity reading is obtained, and then each patient begins taking the assigned medication for 3 days. Skin sensitivity readings are taken at 1, 2, 3, 4, and 8 hours following the first dose. The percentage inhibition of skin sensitivity reaction (reduction in swelling of the area where the allergen is applied compared to the baseline) is shown here for each of the 20 patients.

(A negative value means there was an increase in swelling compared to the baseline.)
a. Compare means and standard deviations by time period for the two treatment groups.
b. Plot these data showing the mean percentage inhibition by time for each treatment group. Does the antihistamine group appear to differ from the placebo group?

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Time (hours) Treatment Patient Antihistamine1 10.5 28.2 15.3 43.0 29.0 41.2 25.3 27.8 28.0 53.2 43.0 20.8 29.3 52 26.5 614 66 62.8 438 9.6 5.0 28.2 31.6 195 2.3 6-102 27238.1 35.5 18.0 7-12922. 34.0434 34.2 27.1 265 38.8 28.5 17.4 13,0 19.7 23.5 294 39.6 28.9 26 112 18.1 16.5 9.3 L0 150 3.0 -1.5-10.1 20.2 18.3 13.5 10.8 20.6 28.3 252 15.8 15.3 19.8 25.4 313 217 8.0 17.5 26.6 164 5.8 12.7 15.6 29.6 7 -16.628432.7 344 158 94 15.7 22.7 298 232 19.3 .7 217 304 26.1 -12.8.30213 10.6 Placebo 3.0 8.7 4.6 10