I wanted to do a short little (we'll see, won't we?) informative post today about the difference between the terms "average" and "normal," because I think they're confused a lot in our culture, even by those who theoretically should understand them due to their training (i.e., health professionals, who I believe take science and math classes to graduate, whereas I was an English major), as well as by parents who are either unjustifiably concerned about not meeting averages or unsuitably (but understandably) proud at beating them.
This article —
"Average age versus normal range," by Michael K. Meyerhoff
An average (in terms of "mean") is a mathematical construct that takes data, (often) filters out the extreme outliers, adds up all the numbers that are left, and then divides the total by the number of items. We all know this, right? It's just when it gets put into practice that it gets murky.
Normal, on the other hand, is always a range, when referring to "normal distribution," the bell curve shape you would expect to find within a group of data. For instance, it might be normal for a baby to crawl (or scoot, as in Mikko's case!) between six months and ten months. The average time for a baby to crawl, then, might be eight months, but it is still normal for a baby to crawl starting at six months or not until ten months. Six months might be at the far left of the bell curve and ten months at the far right, but both are still within the expected range for crawling.
When I talked about "extreme outliers" in defining average, that's where you get abnormal. I don't really like the term "abnormal," because it sounds pejorative, but I hope you know that I mean by it simply outside the normal, expected distribution. As in, a baby who crawls at four months would be outside the norm and would be an early crawler. A baby who didn't crawl (or scoot or walk) until fourteen months would be a late crawler. Their age of crawling would not be normal and would fall outside the expected bell curve distribution. The babies themselves might still be perfectly healthy (more on that in a minute), or they might not, but it's only at that point that it bears looking into. Up until the end of the "normal" range (barring any other signs pointing toward developmental delays), it's perfectly reasonable for a parent to wait patiently for a child to "catch up" to the children who took a developmental step earlier (note I said "earlier," and not "early").
What I find frustrating is medical professionals and other experts who don't understand the difference between average and normal when it comes to diagnosing problems. For instance, the average length of a pregnancy (or so someone decided) is 40 weeks. The normal length of a pregnancy is 38 to 42 weeks. If a woman is a day past 40 weeks, she is not "overdue" or "late." She is normal. If she is two weeks past her "due date" (a term I wish outlawed), she is still not late! (Again, barring any indications of a problem. Being past the due date is not in itself a problem.)
You also see this with weight gain recommendations, both for pregnant women and for babies. A pregnant woman will gain five pounds one month and be warned off eating fat for the next month. She'll gain only two ounces the next month and be told to increase her fat intake. It's ludicrous. Averages don't work that way! An average is over time, over a large set of data. It doesn't mean that every month is going to exactly match the average. But health professionals (and those trusting them) get it into their heads that the "average" monthly weight gain of a healthy pregnant woman is also the magic number that must be met every month, and it simply isn't true.
There's another fallacy inherent in looking toward an average weight gain and applying that to every woman (or baby or child). No woman is average. I cannot emphasize this enough. An average is a mathematical construct, a calculated midpoint within a set of data. It is not a human being. No individual woman or man is average; no pregnancy weight gain is average; no baby's growth chart is average; no child's development is average. No one meets the average!
Let's take some real numbers as an example.
Play along with me and assume that we determine that 1 and 27 are outside of normal distribution, so we discard them. Now we're left with 6 7 8 10 11 12. We add them up: 54. We divide them by the number of numbers (6) and are left with our average (mean): 9.
Is 6 abnormal because it is not 9? No. It's true that 6 is lower than 9, but it is still within the range of normal. Is 12 too big because it is not 9? No, because it is still normal. Note, too, that 9 doesn't even exist! It is only a theoretical, mathematical construct. It is an average but not an item in itself. (Yes, I chose the numbers this way on purpose to make a point.)
Now, is 27 or 1 outside of normal? In this exercise, perhaps so. Maybe if 1 and 27 represent people with some potential health issue, they should get that looked at. But maybe they're fine, too, and if we had more data to go on it would help determine what the normal, expected distribution might be. Maybe 6-12 are simply occupying that widest part of the bell curve, but 1 and 27 are still within the narrow ends on either side.
You can see this play out in everyday life. For instance, the "average" woman's menstrual cycle is 28 days. Well, fine, but that doesn't mean that my average cycle is 28 days. Mine happens to be 29 days. I am still normal. AND, furthermore, my cycle ranges from 27 days to 34 days. You know what? All those cycles: still normal. Possibly very few of them are 29 days. But the average emerges over time, given enough data. I know that if my period doesn't magically appear after 29 days, that doesn't mean I'm pregnant. I just give it a few more days. If my period comes "early," on day 28, I just shrug and put in my DivaCup. It's all fine. I also don't get bent out of shape that my cycle isn't an average 28 days, because — say it with me — no one is average.
Now, again, this is where outliers come into play. If my cycle average was 23 days, I might in fact have a fertility problem due to a short luteal phase. If my cycles varied wildly, really wildly, from 23 days one month to 38 days the next, that might suggest a hormonal imbalance (or miscarriage or menopause). That's where averages help — averages can assist in setting a range for what "normal" might be, but they don't by themselves define normal.
And just another word about outliers. I want to repost my son's growth chart from when he was 10 months old. Talk about unaverage!
He wasn't even, strictly speaking, normal. You can see he's actually breaking the weight chart. But he was fine. He was healthy, and is healthy, and his growth slowed way down after that point and has remained at almost a plateau (which, again, is totally fine). (You can see more pictures of his chubbiness in development here.)
Mikko also talked and walked later than the average, but still within normal range. We weren't worried. We knew some people who were. He caught on just fine once he started, and proved our lack of worry correct. Now, if he still wasn't talking now at 2.75 years old, I probably would have gotten his hearing checked again or looked into other physical problems that might exist. But, even then, there are children who for whatever reason choose not to speak for longer than is "normal" and end up fine. It's one of those things where, if it's really worrying you, it's probably best to check, because there might be an undiagnosed hearing problem or similar. But if everything seems fine otherwise — it probably is. And, on the flip side, if your baby starts talking or walking "early" but still within the normal range, go ahead and brag — why not? But just know that it doesn't indicate anything about meeting future developmental milestones (or your prowess as a parent — but you already knew that, didn't you?).
My point is this: If your child is within the range of normal (or your weight, or your cycles, or times your child breastfeeds per day, or hours your kids sleep, or length of your pregnancy, or progression of your labor, or whatever it is), and you don't see any reason to be worried — and even if you're outside the range of normal but you believe you have good reason to be (for instance, we factored in that both Sam and I are taller than average — but still normal! — to our interpretation of Mikko's large size) — then don't sweat it if you're not hitting the average in every respect. No one does.
We're all normal that way.
I want to include a tiny disclaimer that I am not a health professional, and please don't take the word of a blogger as reason not to have any health concerns checked out by someone who's qualified. Just don't let anyone bully you into thinking average is the same as normal, because it isn't. So there. I'm only trying to empower all those who are within norms to stand up for their right not to be average. And I love all those of you outside the norms, too, because I'm there as well in various ways.
When have you been confronted with the confusion between average and normal? Has anyone told you that you or your children weren't normal when you knew everything was fine, thankyouverymuch?