I have a problem in calculating sample size. I did do a small pilot experiment, so this is some sample data with the same structure:
The idea is this: I'm trying to compare 2 school systems. Based on different factors I have paired schools together. So for ID=1 you have 2 schools with either a school method A or school method B. 3 different types of measuring were done for each School. And because a school with method A requires different testing methods than a school with system B, I end up with 6 different measuring types. For each measurement account: a class is tested and the average score (in %) is used. In the end, I want to know which method gives higher grades, and the outcome should say something for all schools (with the same methods of course, compared to each other) in the USA
But to make a proposal I need to give an indication for the sample size, and I am very unsure about how to calculate this. So what I think I should at least know is the variance of the SchoolSystemA_Score and SchoolSystemB_Score, and the effect size I would at least want to know is 5%.
I'm just not really sure how I should split the groups (or shouldn't)
and what way to do this, is
a good way to go?
Sorry this might be very obvious for many, but I've tried to find articles/literature on this but I get very stuck. mostly because I can;t seem to translate it to my dataset.. Could anyone help me with this, very much appreciated!
Code:
df <- data.frame(ID = c(1,2,3,4,5,6,7,8,9),
School = c("A","A","A","B","B","B","C","C","C"),
Test_Method_A = c("1A","2A","3A","1A","2A","3A","1A","2A","3A"),
SchoolSystemA_Score = c(80,75,25,87,65,15,66,90,65),
Test_Method_B = c("1B","2B","3B","1B","2B","3B","1B","2B","3B"),
SchoolSystemB_Score = c(78,56,80,58,65,98,79,55,70))
df
ID School Test_Method_A SchoolSystemA_Score Test_Method_B SchoolSystemB_Score
1 1 A 1A 80 1B 78
2 2 A 2A 75 2B 56
3 3 A 3A 25 3B 80
4 4 B 1A 87 1B 58
5 5 B 2A 65 2B 65
6 6 B 3A 15 3B 98
7 7 C 1A 66 1B 79
8 8 C 2A 90 2B 55
9 9 C 3A 65 3B 70
But to make a proposal I need to give an indication for the sample size, and I am very unsure about how to calculate this. So what I think I should at least know is the variance of the SchoolSystemA_Score and SchoolSystemB_Score, and the effect size I would at least want to know is 5%.
I'm just not really sure how I should split the groups (or shouldn't)
and what way to do this, is
Code:
pwr.t.test(d=d, sig.level=.05, power = .90, type = 'two.sample')
Sorry this might be very obvious for many, but I've tried to find articles/literature on this but I get very stuck. mostly because I can;t seem to translate it to my dataset.. Could anyone help me with this, very much appreciated!