PSY STATS CHAPTER 2

positively skewed

A skewed distribution with the tail on the right-hand side is

negatively skewed

If the tail points to the left, the distribution

cumulative percentages

The cumulative frequencies show the number of individuals located at or below each score. To find percentiles, we must convert these frequencies into percentages. The resulting values are called.

tail of the distribution

The section where the scores taper off toward one end of a distribution is called the

percentile.

When a score is identified by its percentile rank, the score is called a percentile.

17 Complete the final two columns in the following frequency distribution table and then find the percentiles and percentile ranks requested: x f cf c% 5 2 4 5 3 6 2 4 1 3 a What is the percentile rank for x=2.5 ? b What is the percentile rank for x=4.5 ? c What is the 15th percentile? d What is the 65th percentile?

cf c% 20 100 18 90 13 65 7 35 3 15 a. 35% b. 90% c. 1.5 d. 3.5

18 Complete the final two columns in the following frequency distribution table and then find the percentiles and percentile ranks requested: x f cf c% 25-29 1 20-24 4 15-19 8 10-14 7 5-9 3 0-4 2 What is the percentile rank for x=9.5 ? What is the percentile rank for x=19.5? What is the 48th percentile? What is the 96th percentile?

cf c% 25 100 24 96 20 80 12 48 5 20 2 8 a. 20% b. 80% c. 14.5% d. 24.5%

frequency distribution

is an organized tabulation of the number of individuals located in each category on the scale of measurement.

symmetrical distribution

it is possible to draw a vertical line through the middle so that one side of the distribution is a mirror image of the other

rank or percentile rank

of a particular score is defined as the percentage of individuals in the distribution with scores at or below the particular value.

skewed distribution

the scores tend to pile up toward one end of the scale and taper off gradually at the other end

Construct a frequency distribution table for the following set of scores. Include columns for proportion and percentage in your table. 2,7,5,3,2,9,6,1,1,2 3,3,2,4,5,2,5,4,6,5

x 9 8 7 6 5 4 3 2 1 f 1 0 1 2 4 2 3 5 2 p=f/n .05 0 .05 .10 .20 .10 .15 .25 .10 %=p(100) 5% 0% 5% 10% 20 10 15 25 10

10 For the following set of scores 8,5,9,6,8,7,4,10,6,7, 9,7,9,9,5,8,8,6,7,10 a. Construct a frequency distribution table to organize the scores. b. Draw a frequency distribution histogram for these data.

x f 10 2 9 4 8 4 7 4 6 3 5 2 4 1 draw histogram

5 For the following scores, the smallest value is 13 and the largest value is 51. Place the scores in a grouped frequency distribution table, 44,19,23,17,25,47,32,26, 25,30,18,24,49,51,24,13, 43,27,34,16,52,18,36,25,

x f 50-54 2 45-49 2 40-44 2 35-39 1 30-34 3 25-29 5 20-24 3 15-19 5 10-14 1 x f 50-50 2 40-49 4 30-39 4 20-29 8 10-19 6