Confidence Interval on Difference between Means, Independent Groups, Standard
Deviation Known (3 of 3)
Next section: Difference between independent
groups, σ estimated
The 95% confidence interval is: 127 ±
(1.96)(52.836) = 127 ± 103.559
230.56 ≤ μ
_{1}
μ
_{2 } ≤
23.44
here μ
_{1}is the mean for simple RT and μ
_{2}
is the mean for choice RT.
Summary of Computations

Compute M_{d} = M_{1}  M_{2}
 Compute
 Find z (1.96 for 95% interval; 2.58 for 99% interval)
 Lower
limit = M_{d}  z
 Upper limit = M_{d} + z
 Lower limit ≤ μ_{1}  μ_{2 } ≤ Upper
limit
Assumptions:

The populations are each normally distributed.
 σ is known
 Scores are sampled randomly and are independent
Next section: Difference between independent
groups, σ estimated