To solve complex problems, engineers try to identify all of the important variables that might be in play. Working from this list, each variable is analyzed and tested to determine its effect, if any, on the problem, until the root cause of the problem is identified. The root cause is often traced to a dominant variable, a Big Gorilla. Sometimes, however, it’s not possible to clearly identify a root cause, either because an important variable was not on the list, or because the cause is a combination of variables, and that combination was not considered.
Because we are prone to thinking there is always a single silver-bullet solution to every problem (see “The Single-Event Fallacy (Am I Psychic?)” in this post: “I’m Right! (Or Am I?)“), the possibility of a problem being caused by a combination of significant variables is often disregarded, making problem-solving efforts ineffective and even misleading. For example, a scientific study of thimerosal (50% mercury) in vaccinations may conclude that there is no correlation to autism, and the media will then shout, “Vaccinations don’t cause autism!” But this conclusion is not scientifically justified. For example, is there something else in vaccinations — either by itself or in combination with other factors, including thimerosal — that is linked to autism?
Therefore, in addition to all of the standard skeptical questions one should ask about any study (e.g., was there a control group? were statistics used properly? was the study funded by an organization that has a stake in the results?), it’s always good to be cautious about accepting overly broad conclusions from a study where only a single variable was considered.
Regarding autism and vaccinations, researchers have recently identified a correlation between the Haemophilus influenzae type b (Hib) vaccine and autism (“Hypothesis: Conjugate vaccines may predispose children to autism spectrum disorders,” discussed here). Hib can now be added to the list of possible significant variables (see “Off Topic: The Autism Epidemic“) that may play a significant role in the perplexing and devastating puzzle of autism.