stats CHAPTER 2.3.docx

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26 Apr 2012
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CHAPTER 2, 3, DEFINITIONS
Frequency Distribution: an organized tabulation of the number of individuals located in each category
on the scale of measurement
- Shows if scores are generally high or low, concentrated in one area or spread out, allows you to
see the location of any individual score relative to all others
- Can be either a graph or at able
- In either case, same 2 elements presented:
a) Set of categories that make up the original measurement scale
b) A record of the frequency, or number of individuals in each category
With ordinal, interval, or ratio scale #’s are listed in order, with a nominal scale it doesn’t matter
Proportion: measures the fraction of the total group that is associated with each score
- Are often called relative frequencies because they describe the F in terms of N
Grouped Frequency distribution: table presents groups of scores rather than individual scores the
groups or intervals are called class intervals
FREQUENCY DISTRIBUTION GRAPHS
Basically a picture of the information contained in a frequency distribution table
Graphs for numerical scores measured on an interval or ratio scale
a) Histograms
Width of the bar extends to the real limits
b) Polygon
A dot above each score
For a grouped distribution, dot is above the midpoint between interval
Graphs for nominal or ordinal data 9usually non-numerical values)
a) Bar graph
Essentially same as histogram, with spaces between bars
2 SPECIAL FEATURES OF GRAPSH FOR POPULATION DISTRIBUTIONS:
- Relative Frequency: although cannot find the absolute frequency for each score in a population,
can often obtain relative frequencies
- Smooth Curves: when population consists of numerical values from an interval or ratio scale
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