Wednesday, April 16, 2014

God and null hypotheses

Comedian Tim Minchin performs a song, "Thank You God," prefatory to which he tells a story about meeting a fan of his who is a Christian. When asked why he does not believe in God, Minchin says this is part of a more general policy of only believing things for which he has evidence. What he does not acknowledge is that there also is no evidence that God does not exist. Don't get me wrong: I do enjoy the man's comedy. However, if we're being scientific about this, we start with one of two null hypotheses--God exists, or God does not exist--and we cannot reject either. One might argue that one of those hypotheses is the more reasonable starting point, but it is incorrect to claim that the lack of evidence is an unconditional indication that God does not exist (although, to be fair, I'm not completely sure Minchin was trying to make that claim; maybe he was standing up for agnosticism rather than atheism).

Scientists of all kinds avoid any confusion over the conclusions of research by stating the conclusions carefully. You'll often hear the statement, "There is no evidence that [blank]," which basically means that if we start with the assumption [not blank], we don't have enough evidence to reject that assumption with any reasonable degree of certainty. That could be the case after hundreds of peer-reviewed studies have attempted to demonstrate [blank], or it may be that no one has even tried. Either way, "There is no evidence that [blank]" is not at all the same claim as "There is evidence that [not blank]" and should not be treated as such. Case in point: when my firstborn was an infant, I heard from more than one source that there is no evidence that allowing a baby to "cry it out" causes any lasting psychological damage, but I wasn't about to let my son cry for hours at a stretch.

I think it is common for null hypotheses to go unnoticed or unacknowledged. There's always some kind of default belief. Consider the vaccination scare, still active in some quarters. I don't think that childhood vaccinations cause autism, and that conclusion is predicated on the belief that we shouldn't think that vaccines cause autism unless we have some good reason to do so. One could take the opposite belief as the default, once the possibility of a connection is raised: that vaccinations do cause autism, or some other kind of harm, unless we have strong reason to believe otherwise. I'm not sure if that belief is thoroughly unreasonable, but it is certainly subject to criticism. Such as: given all of the potential causes and potential effects in the universe, any pair chosen at random are extremely unlikely to be related, and therefore the reasonable default belief is that there is no causal relationship between any pair of randomly chosen events. And why are we focusing on autism in particular? Why not other disorders or diseases, or even positive effects, for that matter? Why not take the default belief to be that childhood vaccines cause pattern baldness later in life? And so forth. Apart from the reasonableness of the null itself, adopting the wrong null is costly if there is insufficient evidence to reject the null. If you avoid vaccines because you believe they cause autism, you risk disease that vaccines can prevent (and we have very good evidence for that).

Back to Tim Minchin: it hardly makes sense not to believe anything without evidence. A more defensible statement is that one will not deviate from some kind of baseline beliefs without sufficient evidence. Then the origin of these baseline beliefs becomes the issue. These baseline beliefs are often unstated and may even be subconscious. I doubt that the anti-vaccination crowd is thinking things through in the way I describe above. Opposition to vaccinations may arise from a fundamental belief in the ability of the human body to heal itself under some kind of natural conditions, or from a distrust of the medical establishment's ability to improve health in a substantive way. I suspect that anyone considering the vaccination question has some kind of predisposition toward one side of the debate or the other, and that this predisposition often goes unarticulated.

I can imagine all kinds of baseline beliefs that fuel conflict over social and political issues. For example:
  • People are basically good (or bad)
  • Government agencies are generally corrupt (or trustworthy)
  • Life on Earth is generally getting better (or worse)
One can find indications of any of these things but nothing like definitive proof. If we think about beliefs scientifically, the way to get evidence for something is to assume the opposite and then demonstrate that the data are inconsistent with that assumption. There is no further scientific guidance in forming the null hypothesis: it's just the thing you are trying to disprove. Of course there will always be some reason why one chooses to look for evidence of one particular thing, but this cannot be reduced to a purely logical exercise. I would like to see more explicit acknowledgement of all sorts of baseline beliefs: e.g., the anti-vaxxer says, "I oppose vaccinations because I think medical science is full of it," or the research scientist says, "I am trying to prove this result because it would be neat if it were true."

Tim Minchin's disbelief in God is a matter of faith. Nothing wrong with that, and he can try to argue that this belief is somehow better or more reasonable than the opposite belief. But he can't claim that he is on the side of objective truth.