Statistics for Psychology!
Refresher
• With a partner, define all of these terms:– Mean– Median– Mode– Population– Sample– Variable– Range
Which 3 are measures of central tendency???
Central Tendency
• Mean, mode, median• A measure of central tendency is a way of
specifying - central value.• Measures of central tendency are measures of
the location of the middle or the center of a distribution.
• The mean is the most commonly used measure of central tendency.
Standard Deviation
• Measure of diversity or dispersion • Measures variability• It shows how much variation or "dispersion"
there is from the average (mean, or expected value).
• The measures in a study can be placed on a curve– Normal curve– Skewed curves
Calculating Standard Deviation
Normal Distribution
To Remember – Normal Curve
• Mean, mode, and median all fall dead center• Normal curves measure within 3 deviations to
the positive and negative (to the right and left)
• 99.5% of all data will fall within 3 deviations• 95% of all data will fall within 2 deviations• 68% of all data will fall within 1 deviation
Skewed DistributionsA skewed distribution is a frequency graph that is higher on one side
than the other. For instance, a graph of the frequency of ages of people eating Trix cereal is probably higher in the younger ages than the older ages (positively skewed). A graph of the frequency and ages
of people eating Fiber cereal is probably higher in the older ages (negatively skewed).
Using Deviations and Curves
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