Have you ever been talking to someone about some random parenting decision and their logic for why their decision was right sounded something like “and he’s fine so obviously I was right”?
Yeah, me too. And I’m totally guilty of using that logic myself. But what it represents is a flawed logical argument and something that, in scientific research, we call survivor bias or survival bias.
Basically, bias in statistical terms represents anything that can change the results of a study and lead to the wrong conclusion. Survival bias specifically refers to a situation where you only look at data that seems to support one side of a problem and ignores all the other pieces of data. And while it is called “survival” bias, it doesn’t only refer to situations where one group died and the other survived. It can be any situation where one group of data is ignored.
Imagine this: you are planning a trip to Disney World and know your friend has recently visited. So you ask her how bad the crowds are and how long the lines are. And she says “Oh the lines are no problem at all! The parks aren’t very crowded and we never waited more than 20 minutes for any ride!” Obviously, you’d be trilled with this answer and think you were all set with your visit. But when you go, there are wall-to-wall crowds and wait times well over 100 minutes for all the cool rides. What went wrong? Well, looking deeper, it turns out your friend visited in early January, after the holidays were over and when crowds are notoriously low. You, on the other hand, visited in mid-June, during some of the busiest times of the year. When your friend told you what to expect, she just assumed her experience was representative of everyone’s experience and ignored that the other 360 days may be different from the 5 days she visited. This is a prime example of survival bias. Your friend “survived” a trip during a less crowded time and you didn’t look for any data that might have proved her experience wrong.
So what does that look like in more practical terms and not just with an imaginary vacation?
Let’s consider car seats.
I often hear older generations joking about how they survived before car seat or seat belts. Back in the “good old days.” But that is just it. They survived. The reason we started using seat belts and car seats is because scientists, auto makers, and policymakers realized that too many kids and adults were dying as a result of an ever-rising number of car crashes. So while your grandma may remember riding around without their seat belt, we have long accepted that seat belts and car seats actually make life much safer.
However, car seats still have one issue that people are still debating: rear vs. forward facing as your toddlers and preschoolers get older.
The American Academy of Pediatrics recommends keeping all kids in rear facing for as long as possible, until they exceed the height and/or weight restrictions on their car seat. Some states even require rear facing seats until 1 or two years old. However, many parents turn their kids around earlier than recommended. When asked, parents give a variety of answers as to why they turned their kids. Their child is more comfortable. They wanted to see forward. It was easier for school carpool lines. Their sibling was forward facing and they wanted to be like them. But whatever the reason, parents get defensive if you suggest their child should not be forward facing yet – understandably. No parent wants to be made to feel like they are making bad decisions. And through this, you hear a lot of examples of what falls into the survival bias arena. Things along the lines of “Well my son is 15 now and just fine so clearly it was fine to be forward facing.” But what they fail to consider is whether their child was ever in a car accident while in that forward facing seat. If not, then they really aren’t the right data point to consider. What would really determine if rear or forward facing seats are safer is to look at kids who were in accidents.
There is another sad example of survival bias going on right now in Texas and New Mexico. As I write this, there are more than a hundred and sixty cases of measles in the United States in just the first 2 months of 2025. Compare this to the 285 cases in total in all of 2024. Most of these cases are associated with a specific outbreak out of Gaines County Texas. So far, one child has died in the West Texas outbreak. And I’ve heard a lot of variations on “Well I had measles as a kid and was just fine.” But that’s the thing with survival bias. You only hear from the people who survived. If a child died of measles back in the 70s, they aren’t around to tell you about it today. The only people who are around to tell their tale are the ones that came through okay. Somewhere between 1 and 3 children die for every 1,000 children infected with measles. So if you talk to the 997 people who survived measles as a kid, they will tell you it’s not that bad (well maybe…my mom remembers having it as a kid and she remembers being miserable! So she definitely does not recommend.). But then if you talk to the parents of the 3 kids who died, they will tell you that measles was the worst thing that ever happened to them. But in this example, most of the parents of those kids aren’t around anymore to tell their tale because we’ve done such a good job of reducing the number of measles cases over the past 50 plus years. So instead, all we hear from are the survivors.
Survival bias is so easy to succumb to. Because it usually pops up when the risks are small. Most people were fine so all we remember is that they were fine. And it seems like the “good old days” when people didn’t have to worry about the issue. But in reality, people didn’t know about the risks, no matter how small, so they didn’t even know that they were in fact taking a risk. Science is learning every single day. So what seemed totally fine and safe twenty years ago may in fact be a lot riskier than we realized. The risks aren’t new. Things were just as risky twenty years ago as today. The difference is the knowledge. We didn’t know about the risk back then. We know about them now.
I succumb to survival bias all the time.
I had the flu last week. And my symptoms were very minor. My kids had it with me and they had it even easier than I did. So of course, everyone who catches it from us will have a similar, minor cold. It must mean we had a weak strain. Right? Yeah, tell that to my husband. He was more than a little annoyed with us when he got a much nastier version of the flu than we did. Especially after I assured him that the symptoms weren’t bad. Or my mom, who caught it next and completely lost her voice. In a classic case of survival bias, I ignored the evidence that this was a terrible flu season and the virus can be quite nasty and just looked at the experiences of myself and my kids, who didn’t have it too bad. I neglected to consider our vaccination status, our age, how much sleep we had gotten recently, or any other number of factors that could have made our experience easier than my husband or mom.
Remember. Just because one person’s kid was okay doesn’t mean that yours will be. Or just because one person had a mild case of the flu doesn’t mean you will. And that is why it’s so important that each parent understands the evidence behind their decisions and not just the anecdotal experiences.
References
Anderson CD, Nalls MA, Biffi A, Rost NS, Greenberg SM, Singleton AB, Meschia JF, Rosand J. The effect of survival bias on case-control genetic association studies of highly lethal diseases. Circ Cardiovasc Genet. 2011 Apr;4(2):188-96. doi: 10.1161/CIRCGENETICS.110.957928. Epub 2011 Feb 3. PMID: 21292865; PMCID: PMC3080449. https://pmc.ncbi.nlm.nih.gov/articles/PMC3080449/#:~:text=Survival%20bias%20is%20the%20phenomenon,the%20expression%20of%20that%20trait.
https://www.cdc.gov/measles/data-research/index.html
https://www.cdc.gov/measles/signs-symptoms/index.html
https://www.dshs.texas.gov/news-alerts/measles-outbreak-march-4-2025