Ch23Research Flashcards Preview

Research > Ch23Research > Flashcards

Flashcards in Ch23Research Deck (18):

What is correlation?

the value an individual exhibits on one variable is related to the value he or she exhibits on another variable; CORRELATION IS NOT CAUSATION


What is the most frequently used correlation coefficient?

the Pearson product moment correlation


What are the other correlation coefficients?

Spearman's rho and Kendall's tau used with ranked or ordinal #s; phi, Cramer's V, and kappa used for nominal data


What are the major assumptions of correlation coefficients?

1 relationships between variables are assumed to be linear, 2 homoscedasticity, 3 both variables have enough variability to demonstrate a relationship


How are correlation coefficients interpreted?

1 the strength of the coefficient itself, 2 the variance shared by the two variables, 3 the statistical significance of the correlation coefficient, 4 the confidence intervals about the correlation coefficient


What is correlation coefficient?

Magnitude and direction of the relationship between variables expressed mathematically


What is the Pearson product moment correlation?

(r) The average of the cross-products of the z scores for the X and Y variables, ex: relationship between functional variable such as gait velocity and physical impairment variable such as knew flexion ROM in patients with TKA


range for correlation coefficient

-1 (inversely negative) to +1 (directly positive)


When do you use Spearmans's Rho and Kendall's tau correlations?

when both variables are ranked or ordinal


When do you use point-biserial correlation?

with one continuous and one dichotomous variable


What correlation coefficients are used with nominal data?

phi, Cramer's V and kappa


Strength of coefficient

Assumes that the meaningfulness of a correlation is the same regardless of context
.00 - .25 Little of any correlation
.26 - .49 Low correlation
.50 - .69 Moderate correlation
.70 - .89 High correlation
.90 – 1.00 Very high correlation


What is the coefficient of determination?

square of the correlation coefficient, (r^2)
The coefficient of determination is an indication of the percentage of variance that is shared by the two variables


What is the statistical significance of the coefficient?

The probability that the calculated correlation coefficient would have occurred by chance if there was no relationship between the variables


How do you calculate the confidence interval around the coefficient?

Converts the r values into z scores, calculates confidence intervals with the z scores, and transforms the z score intervals back into a range of r scores


Limits of interpretation

Interpretation of correlation coefficients should not extend beyond the range of the original data


What is linear regression?

Prediction of future characteristics from previously collected data; a line showing best fit between variables; variables must be defined as IV or DV


What is the equation for linear regression?

y = bx + a; b=slope a=intercept