Question

Breastfeeding has become popular in the US during the past decade. Today nearly 77% of American mothers breastfeed for some length of time. Some studies indicate that children who are breastfed become more intelligent than those who are bottle-fed. One study examined 5000 men and women born in Japan, the United States and Sweden between the years 1970 and 1980. The subjects were divided into breast fed and non-breast-fed groups, the groups were controlled for socioeconomic status and their IQ scores were measured when each subject reached 30 years of age. The results indicated that the group of subjects who were breastfed had significantly higher IQ scores than those who were not. The researchers believe that the contents of breast milk account for brain growth and thus intelligence.

For this study:
1. Identify the independent and dependent variables in this study.
2. Tell what type of study this is.
3. Why can't the researchers draw a causal relationship between type of food and later intelligence?
4. What might be an alternate explanation for these results?
5. How could researchers design a study to make a causal connection?

Answer 1

1. The independent variable in this study is the type of feeding (breastfed vs. bottle-fed) and the dependent variable is IQ scores.

2. This study is a cross-sectional study, where data is collected at one point in time for both the independent and dependent variables.

3. The researchers cannot draw a causal relationship between type of food and later intelligence because the study only shows a correlation and does not prove that breastfeeding caused the higher IQ scores. There may be other factors affecting the results such as genetics, socioeconomic status, and parenting.

4. An alternate explanation for the results could be that mothers who choose to breastfeed may also have different parenting styles or educational opportunities that could impact their child's IQ.

5. To make a causal connection, researchers could design a randomized controlled trial, where participants are randomly assigned to either the breastfed or bottle-fed groups and all other factors are controlled for to determine if the type of feeding is the cause of the difference in IQ scores.