Flashcards in Lecture 10 Deck (18):
a measure of the strength of association or relationship between 2 variables.
a measure of the average relationship between 2 variables. It is the average cross-product deviation (i.e., the cross-product divided by one less than the number of observations).
Coefficient of determination:
the proportion of variance in 1 variable explained by a 2nd variable. It is Pearson’s correlation coefficient squared.
Cross product deviations:
a measure of the ‘total’ relationship between 2 variables. It is the deviation of 1 variable from its mean multiplied by the other variable’s deviation from its mean.
in general, curvilinearity is a upside-down U shape distribution.
nominal variable that consists of only 2 levels/groups
Refer to situations in which the sample is somehow limited. also called a restricted range.
What are the two fundamental characteristics of correlation coefficients? Be able to define each.
Direction (pos/neg) and magnitude (strength… how close to +1 or -1)
When the correlation coefficient is zero, what is the relationship between the X and Y variable?
What is a perfect positive correlation? What is a perfect negative correlation?
+1 and -1
When would you compute the following correlation coefficients: Pearson product-moment correlation, point-biserial correlation, biserial correlation, phi coefficient, Spearman’s rho? Note: remember the type of correlation depends on the scale of measurement of the X & Y variables (e.g. dichotomous, nominal, ordinal, continuous).
Be able to list and define/describe all of the issues discussed in class that may weaken (or attenuate) the correlation coefficient.
1. Outliers: extreme scores
2. Truncated range: restricted range/variance
3. Curvilinear relationship: nonlinear relationship that Pearson’s r cannot model
nonlinear relationship that person's r cannot model.
Be able to interpret a 95% confidence interval around a sample correlation coefficient.
CI95= The mean +/- (1.96)(standard error of the mean)