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Flashcards in Ch23Research Deck (18):
1

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

2

What is the most frequently used correlation coefficient?

the Pearson product moment correlation

3

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

4

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

5

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

6

What is correlation coefficient?

Magnitude and direction of the relationship between variables expressed mathematically

7

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

8

range for correlation coefficient

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

9

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

when both variables are ranked or ordinal

10

When do you use point-biserial correlation?

with one continuous and one dichotomous variable

11

What correlation coefficients are used with nominal data?

phi, Cramer's V and kappa

12

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

13

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

14

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

15

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

16

Limits of interpretation

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

17

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

18

What is the equation for linear regression?

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