Homework Assignment No. 5: Birth order effects.

First-born children tend to develop language skills faster than their younger siblings. One possible explanation for this phenomenon is that first-born children  have undivided attention from their parents. If this explanation is correct, then it is also reasonable that twins should show slower  language development than single children and that triplets should be even slower. In 1937, Davis found exactly this result. The following hypothetical data demonstrate this relationship. The dependent variable is a measure of language skill at age three. Do the data provide evidence for significant differences between the three populations? Test at the .05 level.

State the null and alternative hypothesis.

Fill in the following table of descriptive statistics.

Descriptive Statistics                                            
                                       N           Mean        SD    
Single
Twin
Triplet                                                                         

Also, complete the following ANOVA table.

Analysis of Variance of Sociability Data                               
Source                                 SS              df             MS              F            
Between Groups
Within Groups                                                                               

If the F is statistically significant at p < .05 place an asterisk next to it and go on to compute a post-hoc test to determine which pairs of means are significantly different.

Write a brief conclusion (interpretation) of the results.