In an Experiment on the Effect of Garlic on Blood

Multiple Choice

In an experiment on the effect of garlic on blood lipid concentrations, adult volunteers with slightly elevated cholesterol levels were randomly assigned to one of four treatments taken daily for six months: raw garlic, garlic powder, garlic extract, or a placebo. The participants' LDL levels (low-density lipoprotein, or "bad" cholesterol, in mg/dL) were assessed at the end of the six-month study period. Summary statistics and a partial ANOVA table for this study are shown here.

$\begin{array}{l}\begin{array} { l c c c } \text { Treatment } & \text { Mean } & \text { Standard Deviation } & \text { Sample Size } n \\\text { Raw garlic } & 142 & 22 & 49 \\\text { Garlic powder } & 137 & 25 & 47 \\\text { Garlic extract } & 137 & 22 & 48 \\\text { Placebo } & 133 & 21 & 48\end{array}\end{array}$


$$\begin{array}{l}\begin{array} { l l r } \text {Source }&\text {df }&\text {Sums of Squares }&\text {Mean Square }&\text {F-Ratio }\\\text { Treatment}&&&659.46\\\text {Error }&&95,457.00\end{array}\end{array}$$
The research question is: Do the data provide evidence that the treatments affect the mean LDL level in this population? What is the null hypothesis for this test?

A) The population mean LDL level after six months is the same for all four treatments.
B) The population mean LDL level after six months is higher among individuals given a placebo.
C) The population mean LDL level after six months is lower among individuals given a placebo.
D) The population mean LDL level after six months is highest among individuals given raw garlic and lowest among individuals given a placebo.