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The researchers want to determine if chocolate consumption during pregnancy had an effect on the infant temperament at an age of six months or not. Thus, the chocolate consumption is the independent variable whereas the temperament of the infants is the dependent variable as it depends on the chocolate consumption by their mothers during pregnancy. Therefore, the chocolate consumption of the mother is the explanatory variable whereas the infants鈥� temperament is the response variable.

In the given study, the researchers did not try to influence the mothers nor the infants. Moreover, the mount of chocolate consumption was decided by the mother鈥檚 itself and thus the researchers did not have control over the mother鈥檚 decisions.

The researchers thus did not assign treatments to the mothers for the study and therefore, this study is an observational study.

In part (b) we found out that the study was an observational study.

It is then not possible to find out if the chocolate consumption is the cause of infants鈥� temperament because the result could be affected by a lurking variable. A possible lurking variable is the mothers鈥� temperament as children tends to have the same temperament as their parents while the mothers鈥� temperament also influence how much chocolate they eat.

If we have to find out the accurate result then the experiment is better because the lurking variable does not influence it.