They found that the average weight at birth of babies whose mother had had a sonogram was significantly lower than the average weight at birth of babies whose mother hadn't had a sonogram. What possible lurking variable is there?

The given question is incomplete as it lacks the options however the proper options are as follows:

1. Whether or not the mother had a sonogram

2. Type of magazine

3. Whether or not as a fetus the baby was having developmental problems

4. Only babies born in LA were in the study

5. Birth weight

Answer:

The correct answer is - whether or not as a fetus the baby was having developmental problems.

Explanation:

The lurking variable is a variable that is not shown or known or not being monitored but has a direct or indirect relation with the effect on the desired variables.

In the given question the sonogram is an independent variable that can be controlled and not depend on the dependent variable. Birth weight is dependent variable that can not be changed or controlled. Developmental problems are not monitored in the fetus or not known but can affect the dependent or independent variable.

Thus, the correct answer is 3.