Question

A baby weighing more than 4000 grams at birth is considered to be large for gestational age (LGA). Gestational diabetes in the mother is believed to be a common risk factor for LGA. In an article published in the New England Journal of Medicine (October 2009), researchers Landon et al. reported a study of 958 women diagnosed with mild gestational diabetes between 24 and 31 weeks of pregnancy who volunteered to participate in the study and they were randomly assigned to one of two groups: 473 to usual prenatal care (control group) and 485 to dietary intervention, self-monitoring of blood glucose, and insulin therapy, if necessary (treatment group). Of the 473 women in the control group, 68 had babies who were LGA, and of the 485 women in the treatment group, 29 had babies who were LGA.

a. Was this an experiment or an observational study? Explain how you are deciding.

b. Identify the explanatory and response variables. Also, for each variable, be sure to identify the kind of variable (categorical or quantitative)

c. Is there statistically significant evidence to suggest the proportion of LGA babies is higher in the control group than in the treatment group?

· State the parameters of interest

· State the test being used and the conditions needed to conduct it · State the null and alternative hypothesis

· State the test statistic and p-value

· State your conclusion in the context of the problem

Answer 1

Given that,
sample one, x1 =68, n1 =473, p1= x1/n1=0.144
sample two, x2 =29, n2 =485, p2= x2/n2=0.06
null, Ho: p1 = p2
alternate, H1: p1 > p2
level of significance, α = 0.05
from standard normal table,right tailed z α/2 =1.645
since our test is right-tailed
reject Ho, if zo > 1.645
we use test statistic (z) = (p1-p2)/√(p^q^(1/n1+1/n2))
zo =(0.144-0.06)/sqrt((0.101*0.899(1/473+1/485))
zo =4.307
| zo | =4.307
critical value
the value of |z α| at los 0.05% is 1.645
we got |zo| =4.307 & | z α | =1.645
make decision
hence value of | zo | > | z α| and here we reject Ho
p-value: right tail - Ha : ( p > 4.3074 ) = 0.00001
hence value of p0.05 > 0.00001,here we reject Ho
ANSWERS
---------------
a.
A observational study is where nothing changes and just record what you see,
but an experimental study is where you have a control group and a testable group.
b.
sample one, x1 =68, n1 =473, p1= x1/n1=0.144
sample two, x2 =29, n2 =485, p2= x2/n2=0.06
c.
null, Ho: p1 = p2
alternate, H1: p1 > p2
test statistic: 4.307
critical value: 1.645
decision: reject Ho
p-value: 0.00001
we have enough evidence to support the claim that the proportion of LGA babies is higher in the control group than in the treatment group.