Question

1. A t-test should be used when the standard deviation of the population is known, whereas a z-test should be used when the standard deviation of the population is unknown. True or False?

2. If r = 0.72, what proportion of the variance in Y is accounted for by it's relationship with X?

A. .72

b. .52

c. .36

d. .85

3.Jane conducts a Pearson correlation to assess the relationship between years of marriage and happiness from data collected from 100 individuals. What's df in this study?

a.98

b. 99.

C. 100

d. Not enough information

4.A study with 46 participants investigated whether there was a relationship between one’s attitude toward giving blood and the number of times one has given blood in a year. The correlation coefficient was r = +0.56. Thus, the rcritrcrit is ±0.288±0.288 True or False?

Answer 1

Answer:

1. False

Because the t-test should be used when the standard deviation of the population is unknown, whereas a z-test should be used when the standard deviation of the population is known. But the above given sentence is exactly contradictory.

2. b. .52

We know that  the proportion of the variance in Y is accounted for by it's relationship with X is given by coefficient of determination( i.e R -squared). Which is square of correlation coefficient r

here r = 0.72 hence = 0.52 ...(rounded to 2 decimals )

3. a.98

The df for pearson corrleation study are df = n - 2

Here n = 100, so df = 100 - 2 = 98

4. False

r critical value can be obtained from the table with alpha=0.05 and df = n-2

here n = 46 so df = 46-2 = 44

r critical value is 0.291 . ( the give value 0.288 is for df=45 which is wrong)