Stat > ANOVA > Oneway, Response=Length, Factor=Drug Use, Graphs > Residual vs. Fits Plot and Normal Plot
both plots look ok, no problems with the assumptions
Step 2: Summary Statistics
Stat > Basic Statistics > Display Descriptive Statistics, Variable=Length, By variables=Drug Use
| Groups | n | Mean | Std |
|---|---|---|---|
| Drug Free | 39 | 51.1 | 2.897 |
| 1st Trimester | 19 | 49.3 | 2.502 |
| Throughout | 36 | 48.0 | 3.601 |
Step 3: Hypothesis Test
Stat > ANOVA > Oneway, Response=Length, Factor=Drug Use, Graphs > Residual vs. Fits Plot and Normal Plot
both plots look ok, no problems with the assumptions
1) α=0.05
2) H0: α1 = α2 = α3=0 (no difference in the mean lengths of the babies)
3) Ha: αi≠0 for some i (some differences in the mean lengths of the babies)
4) p-value=0.000 < α
5) We reject H0, there are some differences in the mean lengths of the babies
Step 4: Multiple Comparison
Stat > ANOVA > Oneway, Response=Length, Factor=Drug Use, Comparisons > check Tukey
| Throughout | 1stTrimester | Drug Free |
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Interpretation: There is a stat. signif. difference between the mean lengths of the babies of Drug Free mothers and those who took Cocain throughout the pregnancy. Other differences are not stat. signif., at least not at these sample sizes.