Psychology2016

Statistics in Psychology A-3

Just by looking at this table, it is clear that typical people drink between four and eight

glasses of water a day.

Tables can be useful, especially when dealing with small sets of data. Sometimes a

more visual presentation gives a better “picture” of the patterns in a data set, and that is

when researchers use graphs to plot the data from a frequency distribution. One common

graph is a histogram, or a bar graph. Figure A.1 shows how the same data from Table A.1

would look in a bar graph. Another type of graph used in frequency distributions is the

polygon, a line graph. Figure A.2 shows the same data in a polygon graph.

THE NORMAL CURVE Frequency polygons allow researchers to see the shape of

a set of data easily. For example, the number of people drinking glasses of water in

Figure A.2 is easily seen to be centered about six glasses (central tendency) but drops

Table A.1 A Frequency

Distribution

Number of

Glasses

Per Day

Number of

People Out of

30 (Frequency)

1 0

2 1

3 2

4 4

5 5

6 6

7 5

8 4

9 2

10 1

histogram

a bar graph showing a frequency

distribution.

polygon

line graph showing a frequency

distribution.

Figure A.1 A Histogram

Histograms, or bar graphs, provide a visual way to look at data from frequency distributions. In this graph,

for example, the height of the bars indicates that most people drink between four and eight glasses of water

(represented by the five highest bars in the middle of the graph).

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Figure A.2 A Polygon

A polygon is a line graph that can represent the data in a frequency distribution in much the same way as a

bar graph but allows the shape of the data set to be easily viewed.

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