15- Correlation

Question 1

correlation

Answer 1

a statistical method used to measure and describe the relationship between 2 variables (when one changes, so does the other)

Question 2

a correlation typically evaluates 3 aspects of the relationship….

Answer 2

1- the direction
2- the form
3- the strength

Question 3

1) the direction consists of POSITIVE and NEGATIVE relationships (describe them)

Answer 3

positive relationship: 2 variables change in the SAME DIRECTION
negative relationship: 2 variables tend to go in the OPPOSITE DIRECTION

Question 4

2) the form

Answer 4

the most common use of a correlation is to measure straight-line relationships (but other forms do exist)

Question 5

3) the strength

Answer 5

correlation measures the consistency of the relationship (the actual number, REGARDLESS OF + or -)

Question 6

Pearson correlation

Answer 6

measures the direction and degree (strength) of the linear relationship between 2 variables

Question 7

steps to finding pearson correlation:

Answer 7

1) measure variability for SSx and SSy
2) sum of the products:
SP= ∑(X-Mx) (Y-My)
3) calculate: r= SP/ √SSx (SSy)

Question 8

R (pearson correlation) should never go past __ or __.

Answer 8

R (pearson correlation) should never go past -1 or +1.

Question 9

correlations are used in a number of situations:

Answer 9

1) prediction
2) validity
3) reliability
4) theory verification

Question 10

what is one of the most common errors in interpreting correlation….

Answer 10

to assume that a correlation necessarily implies a cause-and-effect relationship

Question 11

important aspects to remember involving the RANGE….

Answer 11

1) be cautious when interpreting data that does not represent a FULL RANGE of possible values
2) you should not generalize any correlation beyond the range in the sample
3) there should be a WIDE range of X and Y in the data

Question 12

outlier:

Answer 12

an individual X and/or Y values that are substantially different (larger or smaller) which causes dramatic effect

Question 13

researchers prefer to ______ the correlation and…..

Answer 13

researchers prefer to SQUARE the correlation, and use the resulting value to measure the STRENGTH (%) of the relationship

Question 14

regression towards the mean

Answer 14

extreme score (high or low) tend to be paired with the less extreme scores (more toward the mean)

Question 15

occasionally, a researcher may suspect that the relationship between 2 variables is being distorted by the influence of ________________.

Answer 15

occasionally, a researcher may suspect that the relationship between 2 variables is being distorted by the influence of A THIRD VARIABLE

Question 16

partial correlation

Answer 16

measuring the relationship between 2 variables while CONTROLLING the influence of a third variable by holding it CONSTANT

Question 17

partial correlations formula: (holding z constant)

Answer 17

rxy - z = rxy - ( rxz(ryz) )
/ √ (1-r²xz) (1-r²yz)

Question 18

what is the null hypothesis in a correlation study stating?

Answer 18

no, there is NO correlation [ H0: p=0 ]

Question 19

what is the alternative hypothesis in a correlation study stating?

Answer 19

yes, there is a REAL, NON-ZERO correlation [H1: p≠ 0]

Question 20

what is the degrees of freedom formula for a correlation study?

Answer 20

df= n-2

Question 21

what is the t statistic for a correlation study?

Answer 21

t = r-p / √ (1-r²) / (n-1)