Exam 9: Z-Scores, Percentiles and Effect Size

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.

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

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

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

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

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

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

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

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

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

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.

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.

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.

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