Thursday, January 08, 2009

Teen birth rates up, but nothing to worry about   posted by agnostic @ 1/08/2009 07:48:00 PM


After declining pretty steadily from 1991 to 2005, in 2006 teen birth rates showed a slight uptick. Rather than swallow what the mass media and doomsaying blogosphere infers, read the report for yourself -- what you want to know is contained in the first 5 to 10 pages. Since most people worry about the long-term trend, and where things are going, I've taken data from the report's tables and put them into easy to understand time-series graphs, broken down by race and ethnicity. I'll then address a few of the larger issues.

All birth rates are live births per 1000 women in a given group. I'll only look at births to 15 - 17 year-olds because mothers younger than that are even rarer, and people freak out less about mothers at or above the age of majority. The 18 - 19 graphs look similar, and you can create them yourselves using the NCHS' report and Excel. Update: see the end of the post for the one 18 - 19 year-old graph that is different, which shows birth rates among Hispanic 18 - 19 year-olds increasing since 2000. [End update]

Most of the recent increase is due to 18 - 19 year-old births, so that's another reason not to care about an increase in "teen pregnancy" -- 18 and 19 year-olds are adults. Moreover, there is an increase across all age groups, especially 20 - 24. So, there's nothing special about teens of any age -- the 15 - 17 year-olds increased a bit, while the 18 and 19 year-olds appear to really be part of a larger group of 18 to 24 year-olds. (Nature doesn't adhere to our numbering system, where there's a bright line between 19 and 20.) Births are just up overall, and the closer we get to the female fecundity peak in the early 20s, the stronger the signal is.

First, the NCHS has data going back to 1970, although it is not broken down by race. Still, here is that graph:

There is a downward trend throughout, with a steady oscillation around that trend. So, the rate will probably continue to decline into the following decades, and we shouldn't be fooled by a temporary increase. For the near future, it looks like the rate will remain pretty flat for about 5 years, then start to increase again, with a decrease again after that, all on a downward trend.

Next, the data with race broken down begins in 1980 and includes White, Black, Asian / Pacific Islander, and American Indian / Alaskan Native. The graph with Hispanic ethnicity is further down. Here are the birth rates for Blacks and AIANs, and for Whites and Asians:

Since the graphs look so similar to the all-race graph, we can assume that from 1970 - '79, the birth rate declined across all races. Again, we see a downward trend with a steady oscillation around it. In no case is the 2006 uptick dramatic, and it looks just like it does in the all-races graph. So again, the rates will probably remain mostly flat for the next 5 years, increase, then decrease, following the overall downward trend.

Finally, the data on Hispanic and non-Hispanic groups starts only in 1990. Here are the trends:

The patterns are the same as in the other graphs, so it wouldn't be too risky to assume that, if we had the actual data, they'd look like they do in the first graph back to 1970. There are clear race and ethnic differences -- the Black line is always above the White line -- but the downward trend and presence of oscillations does not have to do with race or ethnicity. Whatever causes them is at a societal level. The only interesting difference in these Hispanic graphs is that non-Hispanic Blacks and Hispanics have switched in the rank order: we now have more of a Hispanic problem than a Black problem.

That should give people a clearer idea of what is going on. It's silly to forecast based on two data-points -- last year and this year -- when there is plenty of other data to help out. The reason people do this is because it allows them to indulge their desire to imagine the end of the world. The slightest aberration or reversal of a reassuring trend is greeted with exhilaration by the declinist junkies -- "So there's hope that the world is doomed after all!"

Furthermore, these data are all on birth rates, not pregnancy rates. We won't know what the teen pregnancy rate was until we have abortion data, and the NCHS says that won't be for awhile. (The most recent data are from 2004.) For all we know, pregnancy rates are the same or lower than before, but more of those who do get pregnant may opt to keep the kid.

I suspect something like that is true based on adolescent sex behavior data that I've already written about. All measures of sluttiness among teenage girls -- having sex at all, having 4+ partners, not using a condom, etc. -- have declined from 1991 to 2007. Indeed, there is no change in any of the measures from 2005 to 2007. See here for the data from the YRBS. This suggets that the 2006 uptick in birth rates was not due to greater rates of bad behavior among teenagers, but to a greater aversion to abortion among today's young people.

A statement by the National Campaign to Prevent Teen and Unplanned Pregnancy hopes for the worst about these YRBS data:

For teens in school, YRBS data for 2005 and 2007 reflected small increases in sexual activity and decreases in contraceptive use that were not statistically significant, but the changes are likely large enough to account for the 3% increase in the teen birth rate (and likely a similar increase in the teen pregnancy rate) between 2005 and 2006.

The part that I've boldfaced is mostly a lie. If you look at the YRBS data in the link above, there is an apparent but non-significant increase of 1.0% in the percent who have had sex, from 2005 to 2007. However, there was also an apparent increase of 1.1% from 2001 to 2003, and of 1.5% from 1997 to 1999 -- greater than the most recent apparent increase, yet which resulted in no uptick in teen births. As for percent who are currently sexually active, there is an apparent but non-significant increase of 1.1% from 2005 to 2007 -- but there were similar increases from 2001 to 2003 (up 0.9%) and 1997 to 1999 (up 1.5%). The same is true for percent who use birth control pills. Only the percent who used a condom the last time they had sex shows an apparent and non-significant decrease that isn't matched by similar apparent decreases in previous years. Again, though, the change is not significant.

Here's what the CEO of the National Campaign told USA Today:

Sarah Brown, CEO of the National Campaign to Prevent Teen and Unplanned Pregnancy, says she is less inclined to believe abortion is driving higher teen birth rates and suggests that increases in high-profile unmarried births in Hollywood, movies and even politics is a significant factor for impressionable teens.

"In the last couple of years, we had Jamie Lynn Spears. We had Juno and we had Bristol Palin. Those three were in 2007 and 2008 and not in 2005 to 2006, but they point to that phenomenon," she says.

You have to admire her candor and pity her desperation: she admits that the purported causes came years after the effect. So, rather than Hollywood influencing a social trend, the already existing social trend began to reach even into Hollywood. After that happens, there may be positive feedback, but let's be clear about who started it. In general, Hollywood doesn't want to influence any social trend -- they want to figure out what the existing trends are and pander to them to get rich. They're greedy capitalists, not mad scientists.

When I am elected dictator, my first campaign to improve the people's mental health will be to censor anyone who, in a mainstream forum, argues that 1) Hollywood is responsible for degrading our morals, 2) poverty causes crime, 3) "it's the parents' fault," or 4) these kids these days don't know what good music is. Ah, to read the newspaper without feeling the urge to strangle 5 of the 6 people quoted -- that oughtta make everyone feel a bit more sane.

Note: here's the graph for non-Hispanic Black and Hispanic 18 - 19 year-olds:

So as with the 15 - 17 year-old case, Hispanics have overtaken Blacks, and also that their rate has been increasing since 2000. This is the only worrisome data -- and yet another reason to slam our borders shut to anyone who didn't graduate college.

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