Confidence Interval on Difference Between Means, Independent Groups, Standard Deviation Estimated (7 of 7)
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Linear combinations of means from independent groups
Summary of Computations
Compute M
d
= M
1
- M
2
Compute SSE
1
= Σ(X - M
1
)² for Group 1 and SSE
2
= Σ(X - M
2
)² for Group 2
Compute SSE = SSE
1
+ SSE
2
Compute df = N - 2 where N = n
1
+ n
2
Compute MSE = SSE/df
Find t from a
t table
.
Compute
(If the sample sizes are equal then n
h
= n
1
= n
2
).
Compute:
Lower limit = M
d
- t
Upper limit = M
d
+ t
Lower limit ≤ µ
1
- µ
2
≤ Upper limit
Assumptions
:
The populations each are
normally distributed
.
Homogeneity of variance
Scores are sampled randomly and
independently
from 2 different populations
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Linear combinations of means from independent groups