Deck 9: Z-Scores, Percentiles and Effect Size

Question 1

A z-score shows how many standard deviation intervals a value falls above or below the mean.

Answer 1

True

Question 2

When comparing the effect sizes of different studies "stronger" always means "better" or "best," regardless of the nature of the different dependent variables in the different studies.

Answer 2

False

Question 3

A percentile is the percentage of the normal distribution exceeded by a particular value.

Answer 3

True

Question 4

If the z-score is minus 0.50, the percentile is:

A)69.15
B)30.85
C)50.00
D)25.00

Question 5

Z-scores enable us to compare outcomes of evaluations that use very different outcome measures.

Question 6

Given the following values, the z-score is: Raw score = 55
Mean = 50
Standard deviation = 5

A)+ 1.0
B)+ 5.0
C)+ .10
D)- 1.0

Question 7

Given the following values, the percentile is: Raw score = 30
Mean = 30
Standard deviation = 5

A)30
B)50
C)0
D)5

Question 8

Given the following values for an undesirable outcome variable such as number of incidents of verbal abuse, the Cohen's d effect size is: Experimental group mean = 5
Control group mean = 8
Standard deviation = 2

A)+ 3.0
B)- 3.0
C)+ 1.5
D)- 1.5

Question 9

Given the following values for a desirable outcome variable such as self-esteem, the Cohen's d effect size is: Experimental group mean = 70
Control group mean = 60
Standard deviation = 20

A)+ 10.0
B)- 10.0
C)+ 0.50
D)- 0.50

Question 10

If a z score has a minus sign in front of it, then it is undesirable.

Question 11

If the percent of the normal curve between the mean and the z-score is .34, then the percentile is .84.

Question 12

If the z-score is 1.19, the percent of the area under the normal curve between the mean and the z-score is:

A)38.30
B)36.43
C)47.13
D)36.21

Question 13

Suppose John scores 70 on self-esteem scale A, and Bill scores 50 on self-esteem scale B.Assuming that the higher the score, the more self-esteem, which of the following statements is NOT an appropriate conclusion about comparing the two boys' level of self-esteem.

A)John has more self-esteem
B)We don't know based on this information alone because the two scales are different.
C)We should subtract each scale's mean from each raw score and then divide by each scale's standard deviation.
D)If scale A had a mean of 60 and a standard deviation of 20, and if scale B had a mean of 80 and a standard deviation of 10, then Bill has more self-esteem.

Question 14

After we calculate the absolute value for Cohen's d we insert a plus or minus sign according to whether the difference between the group means represents a desirable or undesirable effect.

Question 15

The Cohen's d effect size formula is simply a z-score formula, except that instead of comparing one case's score to the group mean in the numerator, it compares two group means in the numerator.