Behavioral Genetics. In the article “Growth references for height, weight and BMI of Twins aged 0–2.5 years” (ACTA Pediatrica, Vol. 97, pp. 1099–1104), the researchers P. Dommelen et al.

determined the size of the growth deficit in Dutch monozygotic and dizygotic twins aged between 0–2.5 years as compared to the singletons and to construct reference growth charts for twins. The following table shows the difference of the height of the twins at various age groups from 0 to 2.5 years.

5.2 4.5 3.2 4.1 4.8 5.0 4.3 2.7 3.4 3.8 4.7 3.9 1.9 2.3 1.0

a. Identify the variable under consideration.

b. Identify the two populations.

c. Identify the paired-difference variable.

d. Are the numbers in the table paired differences? Why or why not?

e. At the 5% significance level, do the data provide sufficient evidence to conclude that the mean heights of twins separately differ?

(Note: d = 3.65 cm and sd = 1.23 cm.)

f. Repeat part

(e) at the 1% significance level.