January 2017
Beginner
882 pages
203h 41m
English
39. Emerald diamonds
The two categories have similar average weight. Weight is unlikely to confound this analysis.
| Level | Number | Mean | Std Dev |
|---|---|---|---|
| VS1 | 90 | 0.4136 | 0.0544 |
| VVS1 | 54 | 0.4081 | 0.0537 |
The two−sample t−test finds a statistically significant difference: VVS1 diamonds cost on average about $112 more than VS1 diamonds.
| Difference | − 112.30 t Ratio | − 2.88504 |
| Std Err | 38.93 DF | 103.4548 |
| 95% CI | − 189.50 to − 35.11 Prob > t | 0.0048 |
Because the interaction is not statistically significant, remove it and refit the model. Without the interaction, the estimated slope for clarity is significant.
| R2 | 0.4974 |
| se | 161.8489 |
| n | 144 |
| Term | Estimate | Std Error | t−statistic | p−value |
|---|---|---|---|---|
| Intercept ... |