26 terms

Frequency Distribution

Organization of data to show the number of times each score occurs in the sample

Ungrouped Frequency Distribution

1. List each individual score or category on the scale in order from lowest to highest or highest to lowest

2. For each score or category, indicate the frequency, or the number of times it occurs in the data set

2. For each score or category, indicate the frequency, or the number of times it occurs in the data set

Grouped Frequency Distribution

1. Scores or vales are grouped into intervals

2. For each interval, indicate the frequency or number of scores

2. For each interval, indicate the frequency or number of scores

Symmetrical

Each half of the distribution is the mirror image of the other half

Normal

Symmetrical, bell-shaped distribution

Skewed

Asymmetrical with a few extreme values on one side of the distribution

Positively Skewed

Many relatively low values and few extremely high values

Negatively Skewed

Many relatively high values, and few extremely low values

Bimodal

Having two distinct peaks

Kurtosis

Flatness or peakedness of the distribution

Platykurtic

Flat

Leptokurtic

Sharply peaked

N =

∑f (sum of all the frequencies, total number of all the scores in the sample)

Proportion =

p = f / N

Percentage of Proportion =

(f / N) x 100

Cumulative Frequency

Sum of the frequencies at and below that category or value

Cumulative Percentage (c%) =

(cf / N) x 100

How many intervals you you usually want? And Equation

1. Usually want around 10 intervals

2. Interval width = (highest value - lowest value) / 10

2. Interval width = (highest value - lowest value) / 10

Percentile and Percentile Rank

Both give information about cumulative percentage (c%)

Percentile

Usually refers to a score corresponding to a particular rank. Ex. For the ungrouped frequency distribution example, the score of 6 is at the 97th percentile.

Someone takes a standardized test and gets a score of 650. The score report shows that the percentile rank is 75. What does that mean?

Only 25% of people who took that test did better. Or. That person did better than 75% of everyone who took that test.

For graphing frequency distributions, the vertical axis (Y) is used...

To display frequency

For graphing frequency distributions, the horizontal axis (X), is used...

To display scores/categories of the variable

Bar Graph

For discrete data; vertical bar centered over each score or category on X axis; adjacent bars do not touch

Frequency Histogram

For continuous data; vertical bar centered over each score or score interval on X axis and bars touch

Frequency Polygon

For continuous data; point centered over each score or score interval on X axis and points are connected by strait lines