# Calculating Cohens d which mean to use?

#### KfStats

##### New Member
Hey everyone!

(Not sure if i posted this right here but I am new here)

So I am going to try and explain this as well as I can but if anything is unclear just let me know. So currently i am busy with research on personality using the Big Five Trait Inventory. The point of the research is to compare my own scores on the traits to the averagescore of the population on each of these traits. I am also to compare my own score to average of the scores given to me by four class members. For both comparisons I have to calculate the cohens d using the formula (X-Mu)/SD. So for the first comparison I know i simply have to grab my own score subtract the population average score and divide it by the standard deviation of the population. But for the second case im unsure as in what to do. Should i take my own score subtract the average of the average of the scores given to me by the four class members and then divide that by the population standard deviation to get the effect-size? can i I still use the populations standard deviation when comparing my score to the scores given to me by others?
Hope you guys can help me.