Each week, we try to review a research article. This week, instead of reviewing an article, we are going to review a type of research. We are doing this because lately, news outlets have highlighted various studies about autism (e.g., autism and prematurity, autism and diabetes, and autism and IVF to name a few). While these findings are certainly interesting, we should point out that all of these studies are correlational rather than causal. Specifically, prematurity does not cause autism but rather it is associated with or correlated to autism.
A correlational study is designed to measure behaviors, outcomes, or characteristics within a sample and then determine through the use of statistics if any relationships exist between or among the variables. This is usually done by surveying a large group of people and comparing the results from within the group. For example, IVF, or in-vitro fertilization has been shown to be associated with autism.We are sure you are not surprised that IVF is also associated with older mothers. Other factors that should be considered when studying IVF include the rate of prematurity, complications with pregnancy, low birth weight. You see, if a family is using IVF, by nature, the parents had difficulty getting pregnant naturally. Thus, other factors may be at play. These factors may impact the later development, labor, and delivery of the fetus. As the author of the study, Dr. Zachor, pointed out, “mothers in her study who had IVF tended to be older — with a median age of 32.6 years. Also significantly, nearly 4% of the children with autism were born prematurely, and about 5% of those had a low birth weight. In the general population, only about 1% of all newborns are delivered with a low birth weight.” Thus, we should use caution when interpreting the results of this study. Other, more salient factors, may be linked to autism. I would want to know how many of those babies had other complications (e.g., reflux, ear infections, fevers) and how many of those babies also had autism.
Another study recently demonstrated that prematurity increased the risk of autism. Before reading the study, think about all of the factors regarding “preemies”. We would expect preemies to have longer hospitalizations when compared to full-term babies. When babies live in hospitals, they are more likely to be exposed to germs and other illnesses that they would not experience in the safety of their home. Preemies are more likely to have disturbed sleep patterns. Hospital lights, noises, and other disruptions make it difficult to sleep comfortably. Preemies are also more likely to have brain bleeds. Finally, preemies are also more likely to weigh less. None of these factors alone (hospitalization, disturbed sleep, low birth weight) cause autism just as being premature doesn’t cause autism. However, the fact that a child is born prematurely increases the likelihood of other complications. More interesting to us is what other issues did those babies have (e.g., reflux, ear infections, fevers) and were those babies also more likely to develop autism?
So your take away today is this: When you read studies, pay careful attention to the nature of the study. Is it a correlational study where researchers have merely conducted a series of statistical analyses and reported a finding? If so, dig deeper to find other variables that may be the real culprit and continue to push scientists to design experimental prospective studies so that we may learn the real causes of autism.
With that, we are off to sip on a glass of wine and ponder the latest research on alcohol consumption and breast cancer.