L8: Correlation

Question 1

Outline the difference between spearman correlation coefficient and Pearsons

Answer 1

Pearson

• calculated directly from the raw scores
• suitable for data on an interval or ratio scale
• highly affected by outliers
• not suitable for skewed data

Spearman

• calculated from the ranking of the raw scores
• suitable for data on an ordinal scale
• marginally affected by outliers
• suitable for outliers

Question 2

Outline density curves

Answer 2

• plots lots of people and lots of data
• area of curve is related to number of people, histogram curve
• displays overall, pattern of distribution
• calculated so they have an area of exactly 1 underneath them

Median= half of the area is below this point, half is above

Quartile= 25% of area is below Q1, 25% of area is above Q3

Mode= position at the peak of the curve

Mean= balancing point of the curve

Question 3

When you have a perfect curve (normal distribution), what is the relationship between the mean the median and the mode?

Answer 3

They are all the same value

Question 4

What is the relationship between the mean, median and mode when you have both positively and negatively skewed data

Answer 4

Positively skewed: mean is higher than the median, which is higher than the mode

Negatively skewed: mode is higher than the median which is higher than the mean