4f) Assuming spanking is a measure of strictness, the reader's statement has a problem because I see a plausible rival alternative hypothesis for this data. I see another reason why older parents might spank less frequently besides the reader's hypothesis that younger parents are more strict.
This statement is the most accurate out of the set from 1 through 4. A Plausible Rival Alternative Hypothesis to the reader's that parental age causes less spanking is that children's age causes spanking and older parents have, on the average, older children so that is why they spank less frequently -- parental age is associated with children's age but parental age does not cause spanking.
Another way to phrase this PRAH is, "Children's age is
associated with spanking frequency with younger children being spanked more
often than older children. Younger parents are more likely to have younger
children so that is why younger parents spank more. There is no proof in this
data to the idea that younger parents are more strict."
This type of PRAH is called the "third variable" or "Z variable" problem since,
besides parental age (the X variable), and spanking (the Y variable), there is a
third variable (the Z variable) which is the true cause of both X and Y.
Sometimes it is diagrammed like this with the arrows read as "associated with"
children's age (z)
\/
\/
(x) parental age > spanking frequency (y)
This is a great example of the third variable problem. However, for truthfulness, I need to point out that Straus (1994) considered this factor of children's by using advanced statistics to consider this factor. He found, even taking children's ages into account, younger parents still spank more than older parents.