Unit 2 Review

Explanatory Variable

attempts to explain the observed outcomes

Response variable

measures the outcome of the study

Scatterplot

shows the relationship between two quantitative variables measured on the same individuals

Form of a scatterplot

linear or curved

Direction of a scatterplot

is positive, negative, or neither

Strength of a scatterplot

is weak, moderate, or strong

Outlier

lies outside the overall pattern

Positively associated

as one increased the other increases

Negatively associated

as one increases the other decreases

Coorelation

mesures the strength and direction of the relationship between 2 quantitative variables; represented by r

Facts on correlation

• r does not change if x and/or y are changed

• positive r = positive association and negative r = negative association

• always a number between -1 and +1

• measures strength of a linear relationship

• is nonresistant

regression line

describes how a response variable y changes as explanatory variable x changes; predicts values of y for given values of x

R-squared

percentage of the change in the y-variable that can be attributed to its relationship with the x-variable

Residual

difference between observed value of y and a value predicted by the regression line; residual = actual y - predicted y

Residual plot

scatter plot of each x-value and its residual value

Influential point

the removal of the point has a large effect on the correlation and / or regression