Comparing Mean

H. Risanto Siswosuarmo

Objective of Lecture

To understand a continuous data To understand paired t test To understand independent sample t-test To calculate using SPSS statistical program To interprete computer output

Independent Sample T-test

1. Used for continuous data2. Comparing two means3. The subjects must be independent

(different), otherwise use paired t-test4. The data should be normally

distributed, otherwise use Wilcoxon rank test

5. If the CL of the both means doesn’t overlap, then it is statistically different (crosses the number of zero)

Example of Independent Sample T testNorplant Vs. IUD

Siswosudarmo and Sri Kadarsih, 1994

Group Statistics

29 38,28 4,42 ,82

31 43,58 5,85 1,05

29 13,307 ,847 ,157

31 13,216 ,817 ,147

29 31,198 5,040 ,936

31 30,848 4,643 ,834

29 367,586 58,248 10,816

31 386,968 67,042 12,041

Study groupnor

iud

nor

iud

nor

iud

nor

iud

Age (years)

PPT

APTT

Platelate Count

N Mean Std. DeviationStd. Error

Mean

Independent Samples Test

1,014 ,318 ,000 -8,00 -2,61

,000 -7,98 -2,63

,033 ,856 ,674 -,339 ,521

,675 -,340 ,521

,511 ,477 ,781 -2,153 2,852

,782 -2,161 2,860

,912 ,343 ,238 -51,935 13,172

,236 -51,785 13,022

Equal variancesassumed

Equal variancesnot assumed

Equal variancesassumed

Equal variancesnot assumed

Equal variancesassumed

Equal variancesnot assumed

Equal variancesassumed

Equal variancesnot assumed

Age (years)

PPT

APTT

Platelate Count

F Sig.

Levene's Test forEquality of Variances

Sig. (2-tailed) Lower Upper

95% ConfidenceInterval of the

Difference

t-test for Equality of Means

Norplant vs. IUD

Siswosudarmo and Sri Kadarsih, 1994

Paired T-test

1. Used for continuous data

2. Comparing two means

3. The subjects must be the same, but different in terms of other characteristic, e.g. time of observation

4. The data should be normally distributed

Paired T-test, Exp

Paired Samples Statistics

46.16 986 5.49

46.46 986 5.43

46.18 972 5.49

47.01 972 5.58

BW at entry

BW, 6 months

Pair1

BW at entry

BW, 12 months

Pair2

Mean N SD

Siswosudarmo and Moch Anwar, 1993

Paired T-test, ExpConfidence Limit

Siswosudarmo and Moch Anwar, 1993

Paired Samples Test

-.48 -.12 .001

-1.00 -.64 .000

BW at entry -BW, 6 months

Pair1

BW at entry -BW, 12 months

Pair2

Lower Upper

95% ConfidenceInterval of the

Difference

Paired Differences

Sig. (2-tailed)