# Correlation

## 23 terms

### Univariate

Descriptive statistics are univariate when they are used to describe the shape, center and spread of the scores we have for a single variable

### Scatterplot

X axis = independent variable
Y axis = dependent variable

### Positive Relationship

Scores on one variable are associated with similar scores on the other variable
High with high and low with low

### Negative Relationship

Scores on one variablew are associated with scores at the opposite level on the other variable
High with low and low with high

### Correlation Coefficient

Statistical measure of the relationship between two variables

### Pearson Correlation Coefficient

Most common (r) - used when both variables are continuous (either interval or ratio)
Measure degree and direction of a linear relationship

### Spearman Correlation Coefficient

Ordinal data and or nonliner relationships

### Point Biserial Correlation Coefficient

One variable is continuous and the other is dichotomous

### Phi Coefficient

Two dichotomous variables

### Conceptually, r =

degree to which X and Y vary together
degree to which X and Y vary separately

### Putting r into words

There is a (strength) (direction) relationship between (name of IV) and (name of DV)

### Words for negative relationships

As IV increases, DV decreases
People who have more IV tend to have less DV
People who are more IV tend to be less DV

### Words for positive relationships

As IV increases, DV also increases
People who have more IV tend to have more DV
People who are more IV tend to be more DV

### Extraneous factors that can affect r

Range of values on one or both variables (restrict range can distort r)
Outliers - extreme scores on one or both variables (esp influential if sample size is small)

### Correlation is not causation

1. X causes Y
2. Y causes X
3. A third variable may be involved as a mediating variable

### r^2 (Coefficient of determination)

Proportion of variance in one variable that is accounted for by the relationship with the other variable; proportion of explained variance

### 1-(r^2) (Coefficient of nondetermination)

Proportion of variance not accounted for

### Uses of Correlation

Validity of a test or measurement procedure
(Does it measure what it is supposed to measure?)

### Uses of Correlation

Reliability of a test or measurement procedure: consistency of measurement

### Interrater Reliability

Correlation of two sets of ratings made by independent observers

### Test-retest Reliability

Correlation of the test given at one time with the same test given again

### Internal Consistency

Correlation of one part of a test with another part

### Uses of Correlation

Prediction (accuracy of predictions directly related to the strength of the correlation)