Suppose that 55% of the approximately 4,000 school-aged children in the county have vitamin deficiency. A nutritionist takes a cluster random sample of 100 those children. They test the children for vitamin
deficiency. They provide the children with vitamin-rich snacks at school for three months, then retest them.
They plan to look at the difference (after – before) between the proportions of children with vitamin
deficiency.
Consider the formula:
OPA-PB =
PA (1 - PA) PB (1 - PB)
+
пA
пр
Why is it not appropriate for the nutritionist to use this formula for the standard deviation of PA - PB?
Choose 1
The samples are not independent of each other.
We cannot assume independence for the students sampled before receiving the snacks.
We cannot assume independence for the students sampled after receiving the snacks.