I’ve just written a book, Cribsheet, on how to use evidence and data to make choices about early parenting — whether to breastfeed or circumcise, the right age for potty training, and so on — and in doing so, I reflected a lot on these vaccine controversies. Based on my review of the evidence and data, I believe vaccines are a good idea.

When I decided to write about vaccines in Cribsheet, I thought about having a one-line chapter which said, “Vaccines are safe and effective.” And then I’d move on to other topics — say, co-sleeping, where the evidence is more nuanced and interesting. But as I thought about it, I realized that this dismissive attitude may be precisely the problem, and the reason why the pro-vaccination side seems to be losing.

Sleep-deprived parents do not generally think in statistical terms.

If you look at anti-vaccination websites (please don’t), many of them seem evidence-based; they cite papers and studies to support their position. On the other side, organizations like the U.S. Centers for Disease Control (CDC) and the American Academy of Pediatrics (AAP) assure people that vaccination is safe. But the latter groups rarely confront the anti-vaccination literature head-on. There is little effort to explain why the papers cited on anti-vaccination websites are problematic. It can end up seeming as though the anti-vaccination side is serious and evidence-based, and the pro-vaccine side is just dismissively insisting that you trust them because they are experts.

In fact, the case in favor of vaccines is based on extensive research and evidence. I know because I read, in detail, a 900-page tome entitled “Adverse Effects of Vaccines: Evidence and Causality,” put out by the Institute of Medicine. This book was a multiyear effort by a huge group of scientists to think really carefully about the possible risks of vaccines. The authors evaluated evidence from more than 12,000 papers, looking for links between vaccines and “adverse events.” They seriously considered all the possible risks. And their analysis is careful, thoughtful, and not dismissive.

The starting point for these authors is the CDC adverse event reporting system, which is an online resource where people can report if they think their child has been adversely affected by vaccinations. If you search on here, you can find all kinds of parent-reported links about vaccine consequences for their children.

Some may argue that these reports are enough to at least show some link between vaccination and some bad outcome — if someone says their child was damaged, isn’t that enough? But evidence of this type is tenuous at best.

Imagine if people believed that cutting an infant’s fingernails was medically dangerous — that it led to illness or other complications. And imagine we set up an adverse event reporting system for fingernail cutting.

In all likelihood, you’d get a very wide range of reports. There would be parents reporting that the day after they cut their infant’s fingernails, the baby came down with a terrible fever. Others would say they had a very liquid-looking poop. You’d get reports of children who didn’t sleep well for days after the fingernail cutting, and others about babies crying uncontrollably for hours.

These would all be true things that happened. But they wouldn’t be causally linked to the fingernail cutting. Sometimes infants get a fever; sometimes they have weird poops. Most babies do not sleep, and others cry a lot. In order to figure out whether there was any real link, you’d need to know the general base rate of these events — how likely people are to report them when there was no fingernail cutting. But that isn’t something we have a reporting system for. There is no website where you can report every time your kid has an unusual poop. And people, particularly sleep-deprived parents, do not generally think in statistical terms. Near fear looms large.

To know in more certain terms, you’d have to piece together whether these adverse events really seem more common among babies whose nails are cut than those whose aren’t. This is especially hard for things that happen all the time, like when a baby cries.

In your fingernail-reporting system, you probably would also learn something. You’d get a lot of reports of finger injury — cuts in need of Band-Aids. This is not something that happens all the time, and there is an obvious mechanism for the connection with nail cutting. So, you probably would conclude that fingernail cutting is linked to accidental finger cutting, which is true (I know from experience).