Chapter 5 - Correlation Coefficient

Correlation Coefficient

A single number describing a relationship

“How are two variables related

Correlation Coefficient Range

-1 to 1

Correlation Coefficient Limitations

1. only good for linear relationships

2. range restriction

3. outliers

Coefficient of determination

Percentage shared by two variables

how much variance in A is explainable by B

Reverse Causation

Causal direction could be opposite from what has been hypothesized

Reverse Causation

Predictor variable ← outcome variable

Reciprocal Causation

2 variables cause each other

spiral effect/cyclical

Reciprocal Causation

predictor variable ← outcome variable

predictor variable → outcome variable

Common Causation

3rd variable influencing both variables

spurious correlation

Common causation

predictor variable ← common cause → outcome variable

Correlation Coefficient equation

Reverse Causation example

Married people are more likely to be happy

alternate explanation: happy people are more likely to attract mates and to be married

Reciprocal Causation Example

marriage and happiness

self efficacy and performance

giving to charity and happiness

Common causation example

Ice cream sales and murder are positively correlated

third variable = heat