# Frequency Distributions - PowerPoint PPT Presentation

1 / 19

Frequency Distributions. PSY 211 8-29-07. Frequency Distribution. Definition: Table/graph showing number of participants in each category. If I gave a 5-point quiz to a class, the distribution of scores might look like this:.

## Related searches for Frequency Distributions

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Frequency Distributions

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

PSY 211

8-29-07

### Frequency Distribution

• Definition: Table/graph showing number of participants in each category

If I gave a 5-point quiz to a class, the distribution of scores might look like this:

Find the proportion (p) of people who have each score. p = f / N

Find the percentage (%) of people who have each score. % = p * 100

If the scores are spread out, it is okay to group them into a range of scores

Some data:

96, 68, 74, 82, 86,

51, 66, 82, 91, 85,

77,89,88,88,61,90,

79,86,80,92,88,69,

44,99,81,82

Turn a frequency table into a histogram:

Scores

Turn a frequency table into a histogram:

f

Scores

Histogram of Quiz Scores

f

Scores

Now turn that histogram (bar graph) into a polygon (shape, line graph)

Polygon of Quiz Scores

f

6

Scores

You could graph relative frequencies (percentages) instead of frequencies

%

Scores

Relative Histogram of Quiz Scores

%

Scores

### Distribution Shape

• Rather than graph an entire distribution, sometimes researchers just describe its shape and provide a few statistics

f

x

f

Symmetrical distributions: look the same on both sides, mirror images

x

f

x

Positive Skew

*Skewed distribution: lopsided, have a tail off to one side

Tail indicates the direction of the skew (+ or -)

f

x

Negative Skew

f

x

Negative Skew

In actuality, frequency polygons look more like these

f

x

f

Symmetrical

x

### Percentile Rank

• Used to describe where a score falls in a given distribution

95th percentile

50th percentile

f

f

x

x

### Finding Percentile Ranks

cf = cumulative frequency, number of people with that score or lower

### Finding Percentile Ranks

c% = cumulative percentage or percentile rank, percent with that score or lower