Definition: Whether and to what degree variables are related
Purpose:
Determine relationships
Make predictions
Limitation: Cannot indicate cause and effect
Problem selection
- Variables to be correlated are selected on the basis of some rationale:
- Math attitudes and math achievement
- Teachers’ sense of efficacy and their effectiveness
- Increases the ability to meaningfully interpret results
Inefficiency and difficulty interpreting the results from a shotgun approach
Participant and instrument selection
- Minimum of 30 subjects
- Instruments must be valid and reliable
- Higher validity and reliability requires smaller samples
- Lower validity and reliability requires larger samples
Design and procedures: Collect data on two or more variables for each subject
Data analysis: Compute the appropriate correlation coefficient
Correlation Coefficients
A correlation coefficient identifies the size and direction of a relationship
Size/magnitude: Ranges from 0.00 – 1.00
Direction: Positive or negative
Interpreting the size of correlations
General rule:
- Less than .35 is a low correlation
- Between .36 and .65 is a moderate correlation
- Above .66 is a high correlation
Predictions:
- Between .60 and .70 are adequate for group predictions
- Above .80 is adequate for individual predictions
Interpreting the size of correlations (cont.)
Criterion-related validity
- Above .60 for affective scales is adequate
- Above .80 for tests is minimally acceptable
Inter-rater reliability
- Above .90 is very good
- Between .80 and .89 is acceptable
- Between .70 and .79 is minimally acceptable
- Lower than .69 is problematic
Interpreting the direction of correlations
Direction
Positive
High scores on the predictor are associated with high scores on the criterion
Low scores on the predictor are associated with low scores on the criterion
Negative
High scores on the predictor are associated with low scores on the criterion
Low scores on the predictor are associated with high scores on the criterion
Positive or negative does not mean good or bad
