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Numerous factors contribute to the smooth running of an electric motor (鈥淚ncreasing Market Share Through Improved Product and Process Design: An Experimental Approach,鈥 Quality Engineering, 1991: 361鈥369). In particular, it is desirable to keep motor noise and vibration to a minimum. To study the effect that the brand of bearing has on motor vibration, five different motor bearing brands were examined by installing each type of bearing on different random samples of six motors. The amount of motor vibration (measured in microns) was recorded when each of the 30 motors was running. The data for this study follows. State and test the relevant hypotheses at significance level .05, and then carry out a multiple comparisons analysis if appropriate.

Short Answer

Expert verified

There is sufficient evidence to support the claim that the population means are different.

Step by step solution

01

Finding Null and Alternative hypothesis

\(\begin{aligned}{l}I = 5\\\alpha = 0.05\end{aligned}\)

The null hypothesis states that all population means are equal:

\({H_0}:{\mu _1} = {\mu _2} = {\mu _3} = {\mu _4} = {\mu _5}\)

The alternative hypothesis states the opposite of the null hypothesis

\({H_1}:\)not all of \({\mu _1},{\mu _2},{\mu _3},{\mu _4},{\mu _5}\)are equal.

02

Finding ANOVA F Value

The overall mean is the sum of all values divided by the number of values:

\(\overline x = \frac{{{n_1}\overline {{x_1}} + {n_2}\overline {{x_2}} \ldots + {n_k}\overline {{x_k}} }}{N} = \frac{{6(13.6833) + 6(15.95) + 6(13.6667) + 6(14.7333) + 6(13.0833)}}{{6 + 6 + 6 + 6 + 6}} \approx 14.2333\)

\(\begin{aligned}{l}MSTr = \frac{{{n_1}{{(\overline {{x_1}} - \overline x )}^2} + {n_2}{{(\overline {{x_2}} - \overline x )}^2} + \ldots + {n_k}{{(\overline {{x_k}} - \overline x )}^2}}}{{I - 1}}\\ = \frac{{6{{(13.6833 - 14.2233)}^2} + 6{{(15.95 - 14.2233)}^2} + 6{{(13.6667 - 14.2233)}^2} + 6{{(14.7333 - 14.2233)}^2} + 6{{(13.0833 - 14.2233)}^2}}}{{5 - 1}}\\ = 7.7138\end{aligned}\)The mean square for treatment is:

The mean square error is:

\(\begin{aligned}{l}MSE = \frac{{({n_1} - 1)s_1^2 + ({n_2} - 1)s_2^2 + \ldots + ({n_k} - 1)s_k^2}}{{N - I}}\\ = \frac{{(6 - 1){{(1.194)}^2} + (6 - 1){{(0.8165)}^2} + (6 - 1){{(0.9395)}^2} + (6 - 1){{(0.4729)}^2}}}{{(6 + 6 + 6 + 6 + 6) - 5}}\\ = 0.9135\end{aligned}\)

The ANOVA F statistic is the ratio of the MSTr and MSE:

\(F = \frac{{MSTr}}{{MSE}} = \frac{{7.7138}}{{0.9135}} \approx 8.44\)

ANOVA Summary

Source

SS

df

MS

F

P

Treatment

(between groups)

30.8553

4

7.7138

8.44

0.000188

Error

22.8383

25

0.9135

Ss/Bl

Total

53.6937

29

03

Concluding using P value

The P-value is the probability of obtaining the value of the test statistic, or a value more extreme. The P-value is the number (or interval) in the column title of the F-distribution table in the appendix containing the F-value in the row \(dfn = I - 1 = 5 - 1 = 4\)and \(dfd = N - I = 6 + 6 + 6 + 6 + 6 - 6 = 25\):

P < 0.001

If the P-value is less than the significance level, then reject the null hypothesis.

P<0.05鈬扲eject \({H_0}\)

There is sufficient evidence to support the claim that the population means are different.

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Most popular questions from this chapter

consider a single-factor ANOVA experiment in which \(I = 3,\,J = 5,{\overline x _{1.}} = 10,{\overline x _{2.}} = 12,\,and\,{\overline x _{3.}} = 20\)find a value of SSE for which \(f > {F_{.05,2,12,}}\) so that \({H_0}\,:\,{\mu _1} = {\mu _2} = {\mu _3}\)is rejected, yet when Tukey鈥檚 procedure is applied none of the \({\mu _{i'}}s\) can be said to differ significantly from one another.

In Example \(10.11\), subtract \({\overline x _{i.}}\), from each observation in the \({i^{th}}\)sample \(\left( {i = 1,...,6} \right)\) to obtain a set of \(18\)residuals. Then construct a normal probability plot and comment on the plausibility of the normality assumption.

Exercise \(10.7\) described an experiment in which \(26\)resistivity observations were made on each of six different concrete mitures. The article cited there gave the following sample means: \(14.18\,,17.94,\,18.00,\,\,25.74,\,\,27.67\) Apply Tukey鈥檚 method with a simultaneous confidence level of \(95\% \)to identify significant differences, and describe your findings \((use\,\,MSE = 13.929)\)

Six samples of each of four types of cereal grain grown in a certain region were analyzed to determine thiamin content, resulting in the following data \((\mu g/g):\)

Wheat \(5.2\) \(4.5\) \(6.0\) \(6.1\) \(6.7\) \(5.8\)

Barley \(6.5\) \(8.0\) \(6.1\) \(7.5\) \(5.9\) \(5.6\)

Maize \(5.8\) \(4.7\) \(6.4\) \(4.9\) \(6.0\) \(5.2\)

Oats \(8.3\) \(6.1\) \(7.8\) \(7.0\) \(5.5\) \(7.2\)

Does this data suggest that at least two of the grains differ with respect to true average thiamin content? Use a level \(\alpha = .05\)

Repeat Exercise supposing that \(\,\,{\overline x _{2.}} = 502.8\)in addition to\(\,\,{\overline x _{3.}} = 427.5.\)

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