In: Statistics and Probability
12. Toothpaste The table shows the costs per ounce (in dollars) for a sample of toothpastes exhibiting very good stain removal, good stain removal, and fair stain removal. At α = 0.05, can you conclude that at least one mean cost per ounce is different from the others?
Using SPSS!!!
Very Good |
.47 |
.49 |
.41 |
.37 |
.48 |
.51 |
Good |
.60 |
.64 |
.58 |
.75 |
.46 |
|
Fair |
.34 |
.46 |
.44 |
.60 |
The following table is obtained:
Group 1 | Group 2 | Group 3 | |
0.47 | 0.6 | 0.34 | |
0.49 | 0.64 | 0.46 | |
0.41 | 0.58 | 0.44 | |
0.37 | 0.75 | 0.6 | |
0.48 | 0.46 | ||
0.51 | |||
Sum = | 2.73 | 3.03 | 1.84 |
Average = | 0.455 | 0.606 | 0.46 |
∑iXij2 | 1.2565 | 1.8801 | 0.8808 |
St. Dev. = | 0.054 | 0.105 | 0.107 |
SS = | 0.01435 | 0.04392 | 0.0344 |
n = | 6 | 5 | 4 |
The between sum of squares is computed directly as shown in the calculation below:
Null and Alternative Hypotheses
The following null and alternative hypotheses need to be tested:
Ho: μ1 = μ2 = μ3
Ha: At least one mean cost per ounce is different from the others
Conclusion
It is concluded that the null hypothesis Ho is rejected. Therefore, there is enough evidence to claim that
at least one mean cost per ounce is different from the others at the α=0.05 significance level.