Finding Confidence intervals

Confidence Intervals

• Confidence interval– centers on the sample means plus/minus

(tcritical)(standard error)

• Result is a range of scores with the sample mean in the center

Confidence Interval: One sample

• CI = M ± (tcritical)(Sm)

Confidence Interval: Two Independent Samples

–CI = (M1-M2) ± (tcritical)( Sm1-m2)

–Sm1-m2 = standard error of difference between the means

Paired or Dependent SamplesStandard error of mean of differences

First member Second member

Differences

A1 A2 A1-A2

B1 B2 B1-B2

C1 C2 C1-C2

D1 D2 D1-D2

E1 E2 E1-E2

Confidence Interval: Paired or dependent samples

• We work with the Differences

• CI = Md ± tcritical smd

• Smd = standard error of mean of differences