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

Additional Psychology Flashcards

 


 

Cards

Term

Correlation

Definition

● Correlation describes the linear relationship

between observed variables.

Term

Computing correlation

Definition

● One way to compute a correlation coefficient is to

convert all the raw scores (both variables) to z

scores.

● This will give us two sets of z scores.

● To calculate the correlation, cross-multiply the

two 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 (the

cross-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 z

score of y, r will be positive.

● The value of r can never be greater than 1.0 nor

less 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 correlation

will tend to be “larger” (nearer 1 or -1).

● When the scatterplot is blobby the correlation will

tend 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 of

the variable and additive random variability,

then as the range of scores decrease the

apparent influence of variability increases.

Term

The influence of the slope

Definition

● For the same reason, the absolute slope of the

original variables is also unimportant.

Term

The influence of linearity

Definition

● The correlation coefficient only measures the

linear relationship between the variables.

● Therefore, if the slope isn't constant

throughout the range of scores, r will decline.

Term

Factors that influence the correlation

Definition

● The strength of the linear relationship between x

and 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 y

becomes more restricted, the value of the

correlation will decrease.

● When samples are pooled, the correlation of

the aggregated data will depend on where the

samples lie relative to one another on both the

x and y variables.

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