In: Statistics and Probability
The compressive strength of concrete is being studied, and four different mixing techniques are being investigated. The following data have been collected to test if the mixing techniques affect the strength of the concrete.
Mixing Technique |
Compressive strength (psi) |
|||
A |
3125 |
3200 |
2800 |
2600 |
B |
3000 |
3300 |
2900 |
2700 |
C |
2865 |
2975 |
2985 |
2600 |
D |
2890 |
3150 |
3050 |
2765 |
a. Find the summary statistics for compressive strength of each mixing technique.
b. State the null and alternative for the above problem.
c. What assumptions are required to perform the hypothesis testing for above problem?
d. Is there any evidence that mixing techniques affect the strength of the concrete at 5% level of significance?
a. Plot comparative boxplot for each type of mixing techniques and interpret the results (use Excel/R to draw the plots).
There is equal variance among the groups.
b. Find the summary statistics for compressive strength of each mixing technique.
Mean | n | Std. Dev | |
2,932.0 | 4 | 281.60 | A |
2,975.0 | 4 | 250.00 | B |
2,856.3 | 4 | 179.28 | C |
2,963.8 | 4 | 170.36 | D |
2,931.8 | 16 | 207.08 | Total |
c. State the null and alternative for the above problem.
The hypothesis being tested is:
H0: µ1 = µ2 = µ3 = µ4
Ha: At least one means is not equal
d. What assumptions are required to perform the hypothesis testing for above problem?
e. Is there any evidence that mixing techniques affect the strength of the concrete at 5% level of significance?
Source | SS | df | MS | F | p-value |
Treatment | 34,379.50 | 3 | 11,459.833 | 0.23 | .8766 |
Error | 6,08,875.50 | 12 | 50,739.625 | ||
Total | 6,43,255.00 | 15 |
The p-value is 0.8766.
Since the p-value (0.8766) is greater than the significance level (0.05), we fail to reject the null hypothesis.
Therefore, we cannot conclude that mixing techniques affect the strength of the concrete.