Correlation

Question 1

Why is Correlation used?

Answer 1

To study the relationship between two continuous variables.

It quantifies the co-relationship between two variables

Question 2

What is Pearson’s correlation coefficient?

Answer 2

rho or p

1: perfectly positively correlated
0: no correlation
- 1: perfect negative correlation

Question 3

Describe the relationship of the correlation p-value for both Pearson’s and Spearman’s correlation coefficient

Answer 3

For any given sample size, there is a direct (positive) relationship between the correlation coefficient and the p-value

As n increases, the p-value decreases for each increasing rho value, creating a steeper, more towards 90* curve

Question 4

Generally in medical research, what does rho represent (in terms of which value are weak etc.)?

Answer 4

rho>0.5 is strong
rho 0.3-0.5 moderate
rho<0.3 weak

Question 5

what are the assumptions of correlation analysis?

Answer 5

1) data points are independent (two separate groups)
2) one data is normally distributed for and given value of the other
3) constant variance (pattern)
4) linear relationship (constant trend)

Question 6

What is the relationship between data in a Spearman’s Rank Correlation Coefficient?

Answer 6

Monotonic: there is either a positive or negative correlation, but this is not in a line as there is no constant trend

Question 7

What does Spearman’s Rank Correlation Coefficient do?

Answer 7

Replaces values with their rank before calculating a correlation coefficient