PSYC 220
Homework 6
1. In a 95% confidence interval, the 95% tells us…
a. The true population value has .95 probability of being in the interval
b. Under repeated sampling, 95% of intervals would contain the true population value
c. We are 95% confident that our interval is the correct one
d. We are 95% confident the null distribution is true
2. As sample size increases…
a. Confidence level goes up
b. Alpha goes up
c. Interval size decreases
d. Interval size increases
3. If the confidence interval for an independent samples t-test contains zero…
a. The confidence level is too high
b. We likely can’t distinguish the effect from zero
c. The interval size is too large
d. Zero is in the critical region
4. The ± 3% we see on many surveys is the direct product of
a. The critical z and the standard error
b. The critical z and the sample size
c. The standard error and the sample size
d. The proportion and the critical z
e. The proportion and the standard error
5. The standard error for an independent samples t-test is the standard deviation of
a. the sampling distribution for the sample mean
b. the sampling distribution for the sample variance
c. the sampling distribution for the alternative hypothesis
d. the sampling distribution for the difference between the sample means
6. The null hypothesis for an independent samples t-test is often:
a. No difference between a sample mean and population mean
b. No difference between a sample and a hypothetical mean
c. No difference between two population means
d. No difference between a proportion and a population mean
7. a) A recent poll of 600 voters found 60% believed that the issue of collusion between the Trump campaign and the Russian government to be “very serious”. Calculate the 99% confidence interval for this estimate. Report the critical value, the SE, and the interval. Report the interval in a sentence.
b) If the poll had instead been conducted with 96 people, would the interval become larger, smaller, or stay the same and why?
8. Personality researchers wondered if there were differences between “dog people” and “cat people” in how extraverted they were. To find out if there are any differences, researchers asked people to self-identify as cat or dog people and then complete a personality inventory. The results of the extraversion test (on a scale from XXXXXXXXXXfor the two types of person are presented below.
“Dog People” Sample: M = 83, SS = 360, n = 10
“Cat People” Sample: M = 74, SS = 720, n = 10
Assuming a normal population, test the hypothesis that dog and cat people are different in extraversion with alpha = .05.
a) Specify the null and alternative hypotheses.
b) Report the df, critical value, SE, & test statistic
c) Report your decision in a sentence.
9. Using the same example from #8:
a) Calculate the 95% confidence interval for this treatment effect. Report the interval in a sentence.
b) Calculate the 99% confidence interval for the same treatment effect. Report the interval in a sentence.
c) Do the two intervals from parts a) and b) tell us different things? If so, what?