Question

A study was conducted to test whether marijuana use impacts your short-term memory. A simple random sample of college students that do NOT use marijuana was taken, and given a memory test in which they were shown items in a particular order then asked to recreate that ordering. A second simple random sample was taken of college students that use marijuana 4 - 7 days per week, and they were given the same memory test.

A higher score on the memory test indicates better memory recall.

μ1 indicates the population mean memory recall score for non-users.

μ2 indicates the population mean memory recall score for marijuana users.

The 95% confidence interval for the difference of means was found to be:

2.5 < μ1−μ2 < 16.4

Can we support the claim that marijuana users have less short-term memory than non-users?

• Yes
• No

Why or why not?

A retrospective study of 157 pairs of twins was performed. The twin pairs each had one male child and one female child. Their birth weights were studied to determine if the male twin was consistently heavier.

The difference in weights was calculated by subtracting the female weight (in ounces) from the male weight (in ounces):

d=xm−xf

After looking at 157 pairs of twins, the study finds the 95% confidence interval for the mean difference of weights (in ounces) is:

-2.7 < μd < 1.1

Can we be reasonably sure that the male twins are heavier than the females?

• Yes
• No

Why or why not?

Answer 1

A) The 95% CI is:
2.5 < μ1−μ2 < 16.4

As the confidence interval does not contain 0, we can say that the population mean memory recall score for non-users is significantly higher than marijuana users.
Hence, we support the claim that marijuana users have less short-term memory than non-users
Answer: YES

B) The confidence interval for the difference in weights is: -2.7 < μd < 1.1
As the confidence interval contains 0, we can say that the difference is not significantly different than zero.
Hence, we cannot be reasonably sure that the difference in weights between male twins and female twins is different.

Answer: NO