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Suppose the compression strength observation on the fourth type of box in Example \(10.1\)had been \(655.1,\,748.7,\,662.4,\,679.0,\,706.9,\,and\,640.0\) and (obtained by adding \(120\) to each previous \({x_{4j}}\)). Assuming no change in the remaining observations, carry out an F test with \(\alpha = 0.5.\)

Short Answer

Expert verified

The compression strength observation on the fourth type of box in Example.

\(\begin{aligned}{l}I{\rm{ }} = {\rm{ }}Number{\rm{ }}of{\rm{ }}categories = 4{\rm{ }}\\\alpha = {\rm{ }}Significance{\rm{ }}level = 0.05\end{aligned}\)

The null hypothesis states that all population means are equal:

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

There is not sufficient evidence to reject the claim that the population means are not equal.

Step by step solution

01

definition of hypothesis

Hypotheses are typically written in the form of if/then statements, such as if someone consumes a lot of sugar, they will develop cavities in their teeth.

Given:

\(\begin{aligned}{l}I{\rm{ }} = {\rm{ }}Number{\rm{ }}of{\rm{ }}categories = 4{\rm{ }}\\\alpha = {\rm{ }}Significance{\rm{ }}level = 0.05\end{aligned}\)

The null hypothesis states that all population means are equal:

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

The alternative hypothesis states the opposite of the null hypothesis

\({H_1};\)Not all of \({\mu _1},{\mu _2},{\mu _3},{\mu _4}\)are equal

Data summary

Samples

\(1\)

\(2\)

\(3\)

\(4\)

Total

N

\(\,6\)

\(\,6\)

\(\,6\)

\(\,6\)

\(24\)

\(\sum x \)

\(4278\)

\(4541.6\)

\(3888.7\)

\(4092.1\)

\(16800.4\)

Mean

\(713\)

\(756.9333\)

\(648.1167\)

\(682.0167\)

\(700.0167\)

\({\sum x ^2}\)

\(3061048.76\)

\(3445823.16\)

\(2618100.11\)

\(2709930.07\)

\(11923802.1\)

Variance

\(2166.952\)

\(1626.9467\)

\(19553.7657\)

\(1589.9337\)

\(7097.4823\)

Std.Dev.

\(46.5505\)

\(40.3354\)

\(139.8348\)

\(39.874\)

\(84.2466\)

Std .Err.

\(19.0042\)

\(16.4669\)

\(57.0873\)

\(16.2785\)

\(17.1968\)

02

divide the number

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

\(\overline x = \frac{{{n_1}{{\overline x }_1} + {n_2}{{\overline x }_2} + ...{n_k}{{\overline x }_k}}}{N}\)

\(\begin{aligned}{l} = \frac{{6\left( {713} \right) + 6\left( {756.9333} \right) + 6\left( {648.1167} \right) + 6\left( {682.0167} \right)}}{{24}}\\ \approx 700.0167\end{aligned}\)

The mean square for treatment is:

\(MS{T_r} = \frac{{{n_1}{{\left( {\overline {{x_1}} - \overline x } \right)}^2} + {n_2}{{\left( {\overline {{x_2}} - \overline x } \right)}^2} + ... + {n_k}{{\left( {\overline {{x_k}} - \overline x } \right)}^2}}}{{I - 1}}\)

\( = \frac{{6{{\left( {713 - 700.9167} \right)}^2} + 6{{\left( {756.933 - 700.0167} \right)}^2} + 6{{\left( {648.1167 - 700.0167} \right)}^2} + {{\left( {648.1167 - 700.0167} \right)}^2}}}{{4 - 1}}\)

\( = 12851.3678\)

Mean square for error is:

\(MSE = \frac{{\left( {{n_1} - 1} \right){s_1}^2 + \left( {{n_2} - 1} \right){s_2}^2 + \left( {{n_k} - 1} \right){s_k}^2}}{{N - I}}\)

\( = \frac{{(6 - 1){{\left( {46.5505} \right)}^2} + (6 - 1){{\left( {40.3354} \right)}^2} + (6 - 1){{\left( {139.8348} \right)}^2} + (6 - 1){{\left( {39.8740} \right)}^2}}}{{24 - 4}}\)

\( = 6234.3995\)

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

ANOVA summary Independent samples \(k = 4\)

Source

SS

df

Ms

F

P

Treatment between groups

\(38554.1033\)

\(3\)

\(12851.3678\)

\(2.07\)

\(0.137795\)

Error

\(124687.99\)

\(20\)

\(6234.3995\)

Graph maker

Ss/BI

Total

\(163242.093\)

\(23\)

\(F = \frac{{MS{T_r}}}{{MSE}} = \frac{{5.2017}}{{2.2475}} \approx 2.31\)

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 Table \(8\) containing the -value in the row\(d\,\,f\,n = I - 1 = {\rm{ }}4 - 1 = 3\)and\(d\,fd = N - I = {\rm{ }}24 - 4 = 20:\)

\(p > 0.10\)

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

\(P{\rm{ }} > 0.05 \Rightarrow Fail\;to{\rm{ }}reject{\rm{ }}{H_0}\)

There is not sufficient evidence to reject the claim that the population means are not equal.

Hence,

There is not sufficient evidence to reject the claim that the population means are not equal.

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  1. Perform an F at level \(\alpha = .05\)
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