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Stats 8 (ch.3 - ch.4)
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Key Concepts:
Terms in this set (17)
correlation
Denoted r, measures the direction and strength of the linear relationship between two quantitative variables x and y.
negatively associated
Two variables are said to be this when above-average values of one tend to accompany below-average values of the other, and vice versa.
explanatory variable
A variable that may explain or influence changes in another variable. Also referred to as an independent variable.
response variable
A variable that measures an outcome of a study. Also referred to as a dependent variable.
positively associated
Two variables are said to be this when above-average values of one tend to accompany above-average values of the other, and below-average values also tend to occur together.
scatterplot
A plot that displays the relationship between two quantitative variables measured on the same individuals. The values of one variable appear on the horizonal axis and the values of the other variable appear on the vertical axis. Each individual in the data appears as the point in the plot fixed by the values of both variables for that individual.
extrapolation
The use of a regression line for prediction well outside the range of values of the explanatory variable x that you used to obtain the line. Such predictions are often not accurate and should be avoided.
least-squares regression line
The line that makes the sum of the squares of the vertical distances of the data points from the line as small as possible.
association does not imply causation
association does not imply causation
intercept
Denoted a in the straight line equation of the form y = a + bx, the value of the response variable y when the explanatory variable x = 0.
regression line
A straight line that summarizes the relationship between two variables, but only in a specific setting: when one of the variables is thought to help explain or predict the other. Often used to predict the value of a response variable y for a given value of an explanatory variable x.
influential
An observation is said to be this for a statistical calculation if removing it would markedly change the result of the calculation.
residual plot
A scatterplot of the regression residuals against the explanatory variable. Helps us to assess the fit of a regression line.
slope
Denoted b in the straight line equation of the form y = a + bx, the amount by which the response variable y changes when the explanatory variable x increases by one unit.
residual
The difference between an observed value of the response variable and the value predicted by the regression line.
square of the correlation
Denoted r2, the fraction of the variation in the values of y that is explained by the least-squares regression of y on x.
lurking variable
A variable that is not among the explanatory or response variables in a study and yet may influence the interpretation of relationships among those variables.
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