Understanding Relationship Strength « phd monkey

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27Jul/11

Understanding Relationship Strength

On relationship strength:
The relationship between two sets of scores has two characteristics: strength and direction. The strength of a relationship tells the amount scores on one variable are related to scores on the other. Strength is stated from .00 to 1.00. The higher the number, (regardless of sign), the greater the relationship. A correlation of .80 is strong, whereas a correlation of .15 is weak. In a textbook relationship, all data points line up in a straight line.

Steinberg (2011), submits two great examples to explain relationship strength:

Example 1
By knowing the temperature on the Celsius scale, we can exactly predict the temperature on the Fahrenheit scale. Thus, the correlation between Celsius and Fahrenheit is 1.00 (p. 422).

A correlation of .00, at the other extreme, indicates no relationship.

Example 2
For example, there is no relationship between adult IQ and shoe size.
Adults with high, medium, or low IQs are equally likely to have small, medium, or large shoe sizes. Thus, the data points fall in a circular “blob.” (p. 422).

Here is how these two scatterplots would look:

Steinberg, W. J. (2011). Statistics alive! (2nd ed.). Thousand Oaks, CA: Sage Publications.

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