Question

Human babies can be examined in the womb using ultrasound. Animal studies have suggested that ultrasound examinations can cause low birthweight. As ultrasound became more common, researchers observed an association in humans as well – babies who were exposed more often to ultrasound in the womb had lower birth weight on average than babies who were exposed less often.

(a) What are the explanatory and response variables? Is this association positive or negative?

(b) Suggest at least one lurking or confounding variable that could explain the association.

Answer 1

(a) Explanatory variable: Number of exposures to ultrasound

Response variable: Birth weight.

With increase in number of exposures, the birth weight reduces, so, the association is negative.

(b) Lurking variable : Health of the baby. if the baby was found unhealthy on first ultrasound, the doctors may do more frequent ultrasound scans to check on the condition of the baby. The baby, because he/she is unhealthy, will have a lower birth weight than usual as well.

Another confounding variable is the mother's health.