Tests of Correlation

Question 1

what are tests of correlation?

Answer 1

tests of correlation are used to determine whether the association between two covariables is significant or not

Question 2

how to work out the strength of a correlation?

Answer 2

a correlation can be positive or negative

the closer the dots are to forming a diagonal line, the stronger the correlation

the strength can be assessed by calculating a correlation coefficient which is a number between -1 and +1 that tells us how closely the covariables in a correlation analysis are related

a perfect positive correlation will have a correlation coefficient of +1 and a perfect negative correlation will have a correlation coefficient of -1

strength may be strong, moderate or weak

Question 3

what is the non parametric test for correlation?

Answer 3

spearman’s rho

Question 4

what is the parametric test for correlation?

Answer 4

pearson’s r

Question 5

reasons for choosing spearman’s rho

Answer 5

the hypothesis states a correlation between two sets of data

the two sets of data pairs of scores from one person (i.e. related data)

the data is ordinal

Question 6

how to complete a spearman’s rho test

Answer 6

1) state hypothesis — either an alternative hypothesis (directional or nondirectional) or a null hypothesis
2) collect and place raw data in a table
3) find calculated value of rho — to use the formula, rank data in column A from low to high and do the same for column B, find the difference between each pair of ranks, square this difference and add the column up
4) identify if the result is in the right direction in relation to your hypothesis
5) find the critical value of rho — using significance level 5%, identify the kind of hypothesis (one tailed test if directional and vice versa), identify the N value which is total number of scores, locate the row in the statistical table that begins with your N level value, the number in the box is the critical value of rho
6) report the conclusion — if the calculated value is equal to or greater than the critical value, the result is significant

Question 7

reasons for choosing pearson’s r

Answer 7

the hypothesis states a correlation between two sets of data

the two sets of data are pairs of scores that are related

the data is interval

the data fits the criteria for a parametric test — the data is interval, the populations are assumed to have a normal distribution and the variances of the samples are assumed to be the same as the participants are related

Question 8

how to complete a pearson’s r test

Answer 8

1) state hypothesis — either an alternative hypothesis (directional or nondirectional) or a null hypothesis
2) collect and place raw data in a table
3) find calculated value of r
4) identify if the result is in the right direction in relation to your hypothesis
5) find the critical value of r — using significance level 5%, identify the kind of hypothesis (one tailed test if directional and vice versa), identify the df value which is total number of scores minus 2 (N - 2), locate the row in the statistical table that begins with your df level value, the number in the box is the critical value of r
6) report the conclusion — if the calculated value is equal to or greater than the critical value, the result is significant