Answer
1) A group of individuals is selected for the research.
2) The sected individuals are observed for a long period of time.
3) The researchers take note of the individuals' behavior, but without attempting to influence them.
4) Finally, the researchers take note of the response variable.
Work Step by Step
1) 160 women were selected for the research.
2) They were observed for a long period. It is not clear in the problem text, but it seems they were observed during the whole pregnancy period (or at least 3 months).
3) According to the problem text, the women reported about their behavior.
4) In the end, the researchers obtained the birthweight.
