An investigator conducts an experiment involving the effects of three levels of a drug on memory. Subjects are randomly assigned to one of three conditions. A different drug level is administered in each condition. Memory is measured 10 minutes after each subject receives the drug. The following scores are recorded. The higher the score, the better the memory. Assume you are doing planned comparisons evaluating drug levels 2 and 3 using a = 0.05 and H 1 is nondirectional. What is your conclusion?
A) accept H 0 ; the drug has the same effect at these levels
B) retain H 0 ; we cannot conclude the drug has a different effect at these levels
C) reject H 0 ; the groups are not significantly different
D) reject H 0 ; the drug has different effects at these levels

Question

An investigator conducts an experiment involving the effects of three levels of a drug on memory. Subjects are randomly assigned to one of three conditions. A different drug level is administered in each condition. Memory is measured 10 minutes after each subject receives the drug. The following scores are recorded. The higher the score, the better the memory.  Assume you are doing planned comparisons evaluating drug levels 2 and 3 using a = 0.05 and H 1 is nondirectional. What is your conclusion?
A) accept H 0 ; the drug has the same effect at these levels 
B) retain H 0 ; we cannot conclude the drug has a different effect at these levels 
C) reject H 0 ; the groups are not significantly different 
D) reject H 0 ; the drug has different effects at these levels

Quizplus · Accepted Answer

With planned comparisons, we are specifically testing for differences between two groups. In this scenario, we are testing for differences between drug levels 2 and 3. Given the scores provided in the table, the mean for drug level 2 is 30 and the mean for drug level 3 is 40. This suggests that there may be a difference between the two drug levels. Using a 2-tailed t-test with a significance level of 0.05, we find that t(8) = -2.31, p = 0.046. Since p is less than 0.05, we can reject the null hypothesis and conclude that the drug has different effects at these levels. Therefore, the best choice is D.

An Investigator Conducts an Experiment Involving the Effects of Three