Psychological
Statistics
Frequency
Distributions
Psy 207
Erwin Segal
Homework: See Homework
Page
Descriptions of Sets
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Frequency distributions: Frequency grouping helps the researcher
see the shape of the distribution of scores
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Frequency distributions
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relative frequency distributions
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stem and leaf displays
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Histograms: graph for grouped frequencies of quantitative
data
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Bar Graphs: for grouped frequencies of qualitative data
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Pie Charts: alternative to bar graphs
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Box Plots
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Frequency polygons: useful substitute for histograms
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More notes on distributions
Start with
frequency distributions
Use the data to construct histograms or frequency polygons
Varying class intervals on a histogram--click
here
One can plot two or more frequency polygons on the same
axes for comparison. These used relative frequencies or proportions.
One can use the same data to plot cumulative frequency
curves
Charts or graphs based on Frequency
Measures include
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Bar Graphs
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Histograms
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Frequency polygons
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Relative frequency (i.e., proportions, percentages) equivalents
to above
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Pie Charts
There are certain general shapes of distributions based on
what is called the density of the scores at different values of the measures.
The height of the curve above the abscissa (x-axis) measures how many scores
have approximately that value.
Normal distribution
The proportion of the area under the curve between any two
values on the abscissa is the proportion of the set of scores that occur
between those two values.
Areas
of the Normal curve--click here
Skewed distributions
Bimodal distribution
A bimodal distribution can be asymmetric as well.
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