PSYC 220: Homework 4

Note: In the case of decimals, round to the nearest hundredths place (ex: 9.37)

- Alpha is the probability of committing a Type I Error if…

- The null distribution is true
- The null distribution is false
- n is larger than 30
- the alternative distribution is true

- We are more likely to reject the null as…

- Alpha goes down
- n goes down
- variation goes down
- the difference between sample and population mean goes down

- Which of the following is true of a one-tailed test?

- It’s more difficult to reject the null than with a two-tailed test
- It’s more flexible than a two-tailed test
- It’s more sensitive than a two-tailed test
- It’s more appropriate when there are competing theories than a two-tailed test

- Which of the following is not a component of Cohen’s D?

- Sample Mean
- Population/Hypothesized Mean
- Standard deviation
- Sample Size

- When we reject the null hypothesis, we are saying that…

- we have proven the alternative hypothesis to be true
- we have proven the null hypothesis to be false
- our sample is too unlikely to have been produced by the null distribution
- our sample had a mean approximately the same as the population
- our sample had a standard deviation smaller than the population

- If our α = .05, we should make Type I Errors ___% of the time?

- 5
- 5
- 95
- .01
- .025

- The population of adults with tablets and/or smartphones get an average of 6 hours

(µ = 6 and σ = 2) of sleep a night. To see whether electronic use was interfering with sleep, researchers had a sample of 25 adults turn off their smartphones and tablets 1 hour before going to bed. This sample got an average of 6.9 hours of sleep a night. Assuming the population is normally distributed, use an alpha of .05 to test the hypothesis that turning off their electronics early increased the number of hours of sleep they got.

- Specify the null and alternative hypotheses.

- Report the critical value, the SE, and the test statistic

- Report your decision in a sentence

- What type of error did you risk making?

- A company uses a productivity measure to assess how efficiently employees use their time at work. The population of employees had an average productivity rating of 55 (µ=55 and σ = 21). To see how working from home (sometimes called telecommuting) would affect productivity the company selected a sample of 49 employees to work from home. Their average productivity rating was 48. Test the hypothesis that working from home affected productivity using an alpha of .01.

- Specify the null and alternative hypotheses.

- Report the critical value, the SE, and the test statistic

- Report your decision in a sentence

- What type of error did you risk making?

- Psychologists have found that in the population, people can store about 7 pieces of information in their short-term memory (µ = 7, σ = 1), normally distributed. Researchers developing a mnemonic device to increase short-term memory used a sample of 9 people to test their device. The average memory from the sample was 8 pieces of information.

Test the hypothesis that the mnemonic device improved short-term memory using alpha = .01

- Specify the null and alternative hypotheses.

- Report the critical value, the SE, and the test statistic

- Report your decision in a sentence

- Calculate Cohen’s D for the effect size. Does it appear small, medium or large?