I am trying to calculate RCI (reliable change index) which I am able to do with a simple formula - SEM*(standard deviation) X SQRT(1-reliability) I have everything I need for this calculation except a reliability number. It's making me crazy.

All I'm trying to do is come up with a reliability coefficient for the 34 client scores below. As I understand it, the reliability should be pretty close to the average (which for the scores below is 83). But using the formulas I'm finding, I keep coming up with weird numbers like 20. Any help at all would be greatly appreciated! Thanks in advance.

Client Score

A 83

B 80

C 80

D 83

E 86

F 80

G 85

H 79

I 80

J 89

K 87

L 90

M 86

N 74

O 86

P 80

Q 73

R 81

S 92

T 87

U 85

V 89

W 84

X 81

Y 78

Z 86

AA 79

BB 86

CC 84

DD 79

EE 81

FF 90

GG 85

HH 89