Try Magic Notes and save time.Try it free
Try Magic Notes and save timeCrush your year with the magic of personalized studying.Try it free
Question

The article “Human Lateralization from Head to Foot: Sex-Related Factors” (Science, 1978: 1291–1292) reports for both a sample of right-handed men and a sample of right-handed women the number of individuals whose feet were the same size, had a bigger left than right foot (a difference of half a shoe size or more), or had a bigger right than left foot.

 Sample L>RL=RL<R Size  Men 2102840 Women 55181487\begin{array}{|c|c|c|c|c|} \hline & & & & \text { Sample } \\ & \mathbf{L}>\mathbf{R} & \mathbf{L}=\mathbf{R} & \mathbf{L}<\mathbf{R} & \text { Size } \\ \hline \text { Men } & 2 & 10 & 28 & 40 \\ \hline \text { Women } & 55 & 18 & 14 & 87 \\ \hline \end{array}

Does the data indicate that gender has a strong effect on the development of foot asymmetry? State the appropriate null and alternative hypotheses, compute the value of χ2\chi^{2}, and obtain information about the P-value.

Solution

Verified
Answered 4 months ago
Answered 4 months ago
Step 1
1 of 4

To test whether or not there is any effect of gender on the development of foot asymmetry, we will use the chi-square test of homogeneity (since the samples have been taken from two separate populations - of men and women).

Let πij\pi_{ij} be the probability of falling into the category described by the ii-th row and jj-th column of the given table (for instance, π11\pi_{11} is the probability that a randomly selected man would have left foot bigger than right foot), for all i{1,2}i \in \{1,2\} and j{1,2,3}.j \in \{1,2,3\}.

We want to test:

H0:π1,j=π2,j, for all j{1,2,3}H_0: \pi_{1, j} = \pi_{2, j}, \text{ for all } j \in \{1,2,3\}

H1:Not all probabilities are as specified in H0H_1: \text{Not all probabilities are as specified in } H_0

at significance level α=0.05\alpha=0.05 (our choice).

More informally, the above hypotheses can be stated as

H0:H_0': Gender and the development of foot asymmetry are not related

H1:H_1': Gender and the development of foot asymmetry are related.

First we need to make sure the assumptions required for carrying out the chi-square test are met, i.e. we need to make sure that at least 80%80\% of cells (i.e. at least 680%=4.8,6\cdot 80\% = 4.8, i.e. at least 5 cells) have expected counts greater than 5.

Let OijO_{ij} be the observed count in row ii and column j,j, let RiR_i be the row total and let CjC_j be the column total, for every i{1,2}i \in \{1,2\} and j{1,2,3}.j \in \{1,2,3\}.
Let also NN be the total sample size (i.e. the "total of totals").

The expected counts, denoted by EijE_{ij} are calculated as

Eij=RiCjN, for all i{1,2} and j{1,2,3}.E_{ij} = \frac{R_i \cdot C_j}{N}, \text{ for all } i \in \{1,2\} \text{ and } j \in \{1,2,3\} .

So, for instance, the expected count in the top left cell is

E11=40(2+55)127=4057127=17.95.E_{11} = \frac{40\cdot (2+55)}{127} = \frac{40\cdot 57}{127} = 17.95.

Create an account to view solutions

Create an account to view solutions

Recommended textbook solutions

Probability and Statistical Inference 10th Edition by Dale Zimmerman, Elliot Tanis, Robert V. Hogg

Probability and Statistical Inference

10th EditionISBN: 9780135189399Dale Zimmerman, Elliot Tanis, Robert V. Hogg
844 solutions
Probability and Statistics for Engineering and the Sciences 8th Edition by Jay L. Devore

Probability and Statistics for Engineering and the Sciences

8th EditionISBN: 9780538733526 (4 more)Jay L. Devore
1,232 solutions
Probability and Statistics for Engineering and the Sciences 9th Edition by Jay L. Devore

Probability and Statistics for Engineering and the Sciences

9th EditionISBN: 9781305251809 (9 more)Jay L. Devore
1,589 solutions
Statistics and Probability with Applications 3rd Edition by Daren S. Starnes, Josh Tabor

Statistics and Probability with Applications

3rd EditionISBN: 9781464122163Daren S. Starnes, Josh Tabor
2,555 solutions

More related questions

1/4

1/7