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correlation

measure the direction and strength of the linear relationship between two quantitative variables.

residual plot

scatterplot of the residuals against the explanatory variable. help asses how well a regression line fits the data.

residual

difference between an observed data value of the response variable and the value predicted by the regression line.

extrapolation

use of a regression line for prediction far outside the interval of values of the explanatory variable x used to obtain the line.

regression line

line that describes how a response variable y changes as an explanatory x changes. we use it to predict the value of y for a given value of x.

negative association

when above average values of one tend to accompany below average values of the other.

positive association

above average values of one tend to accompany above average values of the other, and when below values tend to occur together.

scatterplot

shows the relationship between two quantitative variables measured on the same individuals. data appears as a point on the graph.

explanatory variable

may help explain or influence changes in a response variable.

response variable

measure an outcome of a study.

treatment

specific experimental condition applied to the units.

experiment

deliberately imposes some treatment on individuals in order to observe their responses.

observational study

observes individuals and measures variables of interest but does not attempt to influence the responses.

available data

data that were produced in the past for some other purpose but that may help answer a present question.

designs

arrangements or patterns for producing data.