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