Question

Dr. T. Aich-Sea is a psychologist from Bowling Green University interested in studying altered time perception. For one of her experiments, she creates two groups (with different subjects in each group). One group of subjects does not smoke anything; while another group smokes marijuana. She waits 15 minutes and asks subjects to estimate how much time has just past (in mins). The data are shown below:

    no drug        marijuana

    23            20

    15            18

    12            27

    20            20

    16            34

    15            25

    SS = 78.83        20

                SS = 191.71

Use a t-test to determine if there is a difference between these two groups.

Answer 1

Here, we will use t test for two sample means.

represents mean time for group 1 no drugs

represents mean time for group 2 with marijuana

Test statistic is t =

where SE is =

Where Is sample 1 variance , and is sample 2 variance.

Since absolute value of test statistic is less than absolute of critical value at 5 % level of significance, so we do not reject null hypothesis.

Note that since t has symmetric distribution, so two tailed test critical value at 5 percent is calculated by 2.5 percent from left only.