Posted by Mark on .
A study found that for adults the general selfefficacy scale mean score was 35 and standard deviation was 12. A group of clients (n=14) was measured for their general selfefficacy with the same measure and found having 40 with standard deviation of 20. A group of therapist would like to know if the group selfefficacy mean score is significantly different from the population mean score use p=0.05.

Stats 
PsyDAG,
Z = (mean1  mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.