Effect size

Question 1

Effect size

Answer 1

• the difference in outcomes between intervention and controls, divided by standard deviation
• measure of the difference in point measurements
• commonly used in meta-analysis that summarise the findings from a specific area of research

Question 2

How to measure Effect size

Answer 2

• use Cohen’s d
• standardised difference between two means
• difference between the means M1-M2 divided by standard deviation,s, of either group

Question 3

Effect size grading

Answer 3

• small=0.2
• medium= 0.5
• large= 0.8

Question 4

Interpreting effect size

Answer 4

• assuming the control and experimental group values are normally distributed with same standard deviations, an effect size can be interpreted just like Z score fo standard normal distribution
  e. g if effect size of 1 then this means that the score of the average person in the experimental group is 1 standard deviation above the average person in the control group

Question 5

Common Language Effect Size

Answer 5

• McGraw and Wong
• probability that a score sampled at random from the experimental group will be greater than a score sampled from controls