# Shared Flashcard Set

## Details

Psych 101 Wk4
Midterm 1
13
Psychology
Not Applicable
02/17/2008

Term
 Correlation
Definition
 ● Correlation describes the linear relationshipbetween observed variables.
Term
 Computing correlation
Definition
 ● One way to compute a correlation coefficient is toconvert all the raw scores (both variables) to zscores.● This will give us two sets of z scores.● To calculate the correlation, cross-multiply thetwo sets of z scores and normalize by n.
Term
 The sign of the correlation coefficient
Definition
 ● The denominator of r must be positive, so the sign of r will be determined by the numerator (thecross-product of the z scores).
Term
 The sign and range of the correlation.
Definition
 ● For a particular observation (a pair of scores), when the z score of x has the same sign as the z score of y, r will be positive.● When the z score of x has the same sign as the zscore of y, r will be positive.● The value of r can never be greater than 1.0 norless than -1.0.● The sign of the correlation is given by the slope of the scatterplot.● When the slope is positive, 0 >= r <= 1.● When the slope is negative, 0 >= r <= -1.
Term
 The shape of the scattergram
Definition
 ● When the scatterplot is elongated, the correlationwill tend to be “larger” (nearer 1 or -1).● When the scatterplot is blobby the correlation willtend to be nearer 0.
Term
 The influence of sample means and SDs
Definition
 ● Because correlation is a function of the z scores of the variables, r is not affected by the mean or the standard deviation of the original observations.
Term
 The influence of variability
Definition
 ● As variability decreases, the correlation increases.● As variability increases, the correlation decreases.
Term
 The influence of the range of scores
Definition
 ● All else being equal, the smaller the range of x and y scores, the lower the correlation coefficient.● If each score reflects both the true value ofthe variable and additive random variability,then as the range of scores decrease theapparent influence of variability increases.
Term
 The influence of the slope
Definition
 ● For the same reason, the absolute slope of theoriginal variables is also unimportant.
Term
 The influence of linearity
Definition
 ● The correlation coefficient only measures thelinear relationship between the variables.● Therefore, if the slope isn't constantthroughout the range of scores, r will decline.
Term
 Factors that influence the correlation
Definition
 ● The strength of the linear relationship between xand y.● The strength of any nonlinear relationship between x and y.● The range of the scores across the variables.● Measurement error (and other uncontrolled sources of variability).
Term
 Potential problems with correlation
Definition
 ● Non-normally distributed variables.● Restriction of range.● Nonlinear relationship between variables.● Poor measurement reliability.
Term
 Factors influencing correlation
Definition
 ● The true underlying relationship between x and y.● The range of scores in x and y.● All else being equal, as the range of x or ybecomes more restricted, the value of thecorrelation will decrease.● When samples are pooled, the correlation ofthe aggregated data will depend on where thesamples lie relative to one another on both thex and y variables.
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