People still misunderstand and misuse correlation all of the time. I think the Wikipedia article on the subject still gives one of the better summaries on the subject -
Correlation does not imply causation" is a phrase used in science and statistics to emphasize that correlation between two variables does not automatically imply that one causes the other (though correlation is necessary for linear causation, and can indicate possible causes or areas for further investigation... in other words, correlation can be a hint).I still run across people who ignore that definition and twist it to suit their own needs.
If they disagree with a controversial treatment, such as the GFCF diet, and you say that the treatment has helped your children, they might use the "correlation does not imply causation" line to say that the diet couldn't have caused the changes. Or on the flip side, you have people who think that autism is genetic and take the smallest correlation or appearance of increased risk and immediately jump to the fact that just having a rare genetic condition can cause autism.
Its funny really, even people who claim to base their opinions on science fall into the trap of favoring lines of thought that agree with their opinions and discount those that don't. I, of course, never have that problem and am perfectly rational at all times.....
In my first post I also briefly mentioned a part of my twin daughters history that I don't think I have ever really explained. You see, my older twin daughters experienced a regression at about one year old.
Before the regression, the twins were progressing normally for being twins, which means they were meeting most of their milestones but were slower to start using words (its a twin thing). They also had some decent social skills going and we had actually seen them team up to do something a few times.
But, about a month before their first birthday, we went in for a normal doctors visit and they received their second flu shot. Less than a day later, they both spiked a fever and developed what we thought was a cold. We still don't know what exactly they had but, whatever it was, it was something nasty and they couldn't seem to shake it. They spent the next six to eight weeks or so trying to fight off whatever it was and were just miserable little lumps the entire time. They went from being happy little girls to just sitting and staring.
About two weeks into the cold they both came down with what was most likely rotavirus and we experienced diarrhea like we never had before. And even though the worst of it passed after a week or two, the twins never stopped having issues with loose stools until we put then on the GFCF diet over a year later.
About four weeks into the cold they both developed ear infections and were put on antibiotics. A trip to the emergency room, some perforated eardrums, and a week later they seemed to be coming out of whatever it was and we took them in for a regular doctors visit which is when they received the MMRV shot. The same day as the appointment the mystery illness came back and, over the next several days, they also developed a strange rash that resembled chicken pox on their stomachs. They spent the next two weeks being even more miserable than before.
When they finally managed to kick whatever it was and started feeling better, they were subtly different. They were not as engaging as they were before and the early vocalizations we had heard disappeared. More importantly, they stopped responding to sound the same way. It took up a while to pick up on what was going on, but for several months we thought that they might be deaf.
As a matter of fact, after they failed two hearing tests, there were several audiologists who also thought that they might be deaf. It took a procedure known as an auditory brainstem response (ABR) to establish the fact that they were still physically able to hear. I suspect that this abnormal processing of sound is a large part of the reason that their ability to understand speech and to talk is still very limited to this day.
Now, let me be clear, I don't think that this illness or the vaccines "caused" their autism - I believe that they would have still developed autism like their younger sister did. But I do believe that this illness made their autism worse than it would have been otherwise.
Since this time we have learned a few little facts. Like the fact that a flu shot hasn't been shown to be effective in children under the age of two. Like the fact that thimerosal - which was in the flu shots - probably isn't the best thing to give to very young children. Or like the fact that you really shouldn't give any vaccine to a child who is sick and on antibiotics.
I have also learned more about how the body works and how seemingly unrelated systems can interact. Such as how problems with energy metabolism can be made worse by an abnormal immune system reaction. Did I ever mention that the twins have documented problems with immune disregulation and suspected problems with processing creatine?
Do you know what can happen to a one year old who, under the best conditions, have problems with an overactive immune system and processing energy, add in the extra stress of rotovirus, a nasty cold/flu, and an ear inflection, and then further stress them out by injecting weakened forms of four major childhood illnesses at once with an adjuvant designed to kick the immune system into high gear? For good measure add an undiagnosed food intolerance to milk, deficiencies in basic nutrients such a iron and zinc (most likely caused by the food intolerance), and the GI problems caused by an oral antibiotic and you might just get the perfect storm.
Its no wonder that they looked miserable.
I don't know if we could have down anything differently with the twins. Perhaps if we had, they might be more like their youngest sister. Baby C never had a period of illness like this and never had any sort of regression. She still gets her vaccines but we slowed them down and spaced them out more. She never gets them when she is sick and we never give her more than two at once
So now, five years after the twins regressed, we are still trying to figure out what happened and what we can do to help all three girls. I know that science has exonerated vaccines from having anything to do with autism but, and this is the important part, science deals with overall trend and large groups of people. Large studies are good at detecting overall trends but can't necessarily tell you what happened with an individual child.
So even though I know, understand, and accept the fact that - for the majority of children - vaccines are perfectly safe and that I know that my children would still have autism without the vaccines, I still have my doubts. Maybe there are other children out there who, like my twins, simply couldn't tolerate what they were given at the exact moment it was given.
Who knows, maybe I am completely wrong about this entire sequence of events and the regression would have happened regardless of what we did. But that is unknowable and all I can go on is what seems to be the sequence of events. All I know is that the two separate children reacted the same way to the same events at the same time and there appears to be a correlation in spite of all of the science saying that there should be none.
But, as I said at the start, correlation isn't causation.