26 Correlation

Question 1

often first step in identifying causal relation (establish degree and direction of relationship/covariation between 2+ variables)

Answer 1

correlation

Question 2

correlation useful in health sci to:

Answer 2

determine reliability/validity, find/express how health probs related to bio/enviro/diet factors

Question 3

stat of magnitude and direction of association between 2 variables

Answer 3

correlation coefficient

Question 4

common coefficients?

Answer 4

Pearson’s r, Spearmans rho

Question 5

what is r?

Answer 5

both x and y measure on an interval or ratio scale, assume variables are normally dist. and have linear relation, convert to z score and corrects for x/y having diff means and SDs

Question 6

what is p (rho)?

Answer 6

both x and y measure on/transformed to ordinal, can readily convert variable on higher scale to ordinal scale

Question 7

what is phi?

Answer 7

both x and y measure on nominal

Question 8

square of correlation coefficient is called:

Answer 8

coefficient of determination

Question 9

r=

Answer 9

sum of ZxZy / n (or n-1 for sample)–>n= # paired measurements

Question 10

r>__ is quite high, < __ is weak

Answer 10

0.7; 0.3

Question 11

rho=

Answer 11

1-[6sum d^2/(n^3-n)]

Question 12

uses of correlation?

Answer 12

prediction, reliability and validity of assessment (test retest and inter observer), estimating shared variance

Question 13

square of correlation coefficient, proportion of variance in one variable accounted for by other

Answer 13

coefficient of determination (r^2)

Question 14

remember criteria of causal relationship:

Answer 14

antecedence, covariation, elimination of rival explanations

Question 15

calculate probabilities with:

Answer 15

t test

Question 16

need to show correlation coefficient has ___

Answer 16

statistical significance

Question 17

how show stat significance?

Answer 17

table of critical values for pearsons r, degrees of freedom for correlation is n-2