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= How do I compute Mean Square Error (MSE)? =  = How do I compute Mean Square Error (MSE) in EXCEL or SPSS? = 
How do I compute Mean Square Error (MSE) in EXCEL or SPSS?
Mean square error or MSE is frequently requested by journals as a companion statistic for ANOVA and, especially, ttests. MSE is the average intragroup variance. MSE is outputted in ANOVA tables but can be computed using a weighted average of the group variances.
Fo G groups with the ith an SD, $$SD_text{i}$$ and sample size $$N_text{i}$$,
MSE = $$\frac{\sum_text{i} (N_text{i}1) SD_text{i}^text{2}}{(\sum_text{i}N_text{i})G } $$
which equals $$\frac{\sum_text{i} SD_text{i}^text{2}}{G} $$ in the special case of equal group sizes.
In EXCEL, suppose we have two groups (A and B ) in cells A1:A100 and B1:B100 respectively, MSE can then be computed using
MSE =(SQRT(((COUNT(A1:A100)1)+(COUNT(B1:B100)1)))*(AVERAGE(A1:A100)AVERAGE(B1:B100)))/(SQRT((COUNT(A1:A100)1)*POWER(STDEV(A1:A100),2)+(COUNT(B1:B100)1)*POWER(STDEV(B1:B100),2)))