Friday, September 28, 2012

The Great Migration

The U.S. Census Bureau analyzed data on population change, by race, for two key periods that characterize The Great Migration (1910-1970) during which blacks residents moved out of the southeast.

The color of map bubbles represents the percentage point change in black population in a given city between 1910-1940 (left) and 1940-1970 (right). Darker orange shows that the black population increased as a share of the city's population. Darker blue shows that the share decreased.
Image source
What I find interesting about the 1940-1970 chart is that New Orleans and Atlanta (and, to a lesser extent, Augusta and Chattanooga) both buck the otherwise nearly universal southern trend. Each city saw an increasing proportion of black residents 1940-1970.

However, it is important to note two key caveats in the data:

  • Population shares may have changed due to migration or as a result of natural increase (births, life expectancy), though most of the change is attributable to migration.
  • Data are shown only for cities "that were either in the top 100 cities in the country or top 3 of a state and had a Black population of at least 100 people." This means that some change shown on the chart may have been a shift from suburbs-to-cities or vice-versa.

Friday, September 14, 2012

Data link roundup (week of September 14, 2012)

The week's top data analysis links...


In an article I published on Examiner, I debunk the data Hanna Rosin uses to make the case that there is an "End of Men."


New data released by the CDC shows that in 2010 the teen birth rate fell to its lowest recorded level in U.S. history. (Records for all births go back to the 1920s. Records for teen births are reported from 1960.)
Source: CDC
A brief summary of the CDC report can be found here.

Monday, September 10, 2012

Not the end of men

Every time I hear Hanna Rosin bemoan the "end of men," I cringe a little. I rolled my eyes at the dubious statistics rounded up in her Atlantic article and TED talk, and I expect to see similar mis-applications of data in her new book 'The End of Men: And the Rise of Women,' due out tomorrow.

To be clear: There is no "end of men."

While the United States may finally be nearing something more like gender equity, the sky is most certainly not falling for the Y chromosome.

Scare mongers cherry-pick statistics to prove their point, citing for example that:
"Most managers are now women too."
~H. Rosin, The Atlantic, July/August 2010
This statistic, by the way, is not true.

There are 8.19 million men in management occupations, compared with 5.25 million women, according to the 2010 American Community Survey. Within management, there are 1.44 million male "top executives" while there are only half a million women in similar roles.

With 50 percent more men than women in management overall, and nearly three times as many in top executive positions, one wonders where the "end of men" camp found their statistics.

It is true, however, that women are enrolling in and completing college at higher rates than their male peers. That said, the wage gap between men and women actually increases along the educational spectrum.
Source: U.S. Bureau of Labor Statistics, median weekly earnings of
full-time workers by sex and education level in 2011, author's calculations
Two trends jump out in this chart, which shows median weekly earnings of full time workers in 2011. First, higher levels of educational attainment correlate strongly with higher earnings. Second, there is a persistent wage gap between women and men across all educational levels. In fact, while women with less than a high school education are paid, on average, 20 percent less than their male counterparts, women with advanced degrees are paid only 74 cents for every dollar paid to men with similar educational qualifications.

One of the most common arguments for why women earn less than men is that they are more likely to work part time. This chart shows only full-time workers. Another, older, argument is that women historically had lower levels of educational attainment. These data also correct for any imbalances in education.

What remains is:
  • Differences in occupational classifications (and there remain persistent differences in men's and women's work types).
  • Differences in work history (including length of career and time spent not working, especially working mothers for maternity leave), although plenty of research shows that even time away from the job cannot explain all of the difference in the gender wage gap. The wage gap exists even between men and women who have never had children.
  • Discrimination, which can be both wage discrimination by employers and self-discrimination in women expecting, and thus demanding, lower starting salaries during job negotiations
Admittedly, sensational headlines in late 2010, sparked by a study from marketing firm Reach Advisors, trumpeted the findings that young, urban women out-earned their male peers by 8 percent.

Many were quick to jump to the conclusion that the "gender wage gap" is fiction. Yet even the study authors admit that the data for that one, tiny, cohort (single, childless, women under age 30, living in major metropolitan areas) merely reflect increasing female educational attainment and do not reflect a pattern of reverse discrimination, or even that the gender gap is gone.

Persistent wage gaps and gender-segregated occupations hardly spell the demise of men.

Rosin also highlights the loss of manufacturing jobs as implying that burly men are no longer needed (her implication, not mine). However, there are more than 10 million manufacturing jobs in the United States, and the number has been growing over the past year, not declining.

rumors of men's demise have
been greatly exaggerated

This does not mean that all women are victims. This does not imply that all men discriminate. This does not show that all women are weak, or that all men are powerful.

What this fact-checking does show is that rumors of men's demise have been greatly exaggerated.

In a nation where women have had the right to vote for less than 100 years, growing signs of gender equality should be praised, not turned into a sensational headline that re-ignites the gender war.

There is no evidence that men are becoming obsolete, and by painting the data in that light, Rosin does a disservice to both women and men.

I plan to read Rosin's book, but with a critical eye for the details. To date, the "facts" used in building the case for the "end of men" have been dubious at best.

Friday, September 7, 2012

September birthdays

Are your Facebook birthday reminders lighting up this month? Have you ever noticed that you receive more birthday party invitations and have more cards to send in September than in any other month of the year?

If you have noticed a spike, you are not alone. There is a clear pattern of "birth seasonality" resulting from a "seasonal cycle in fecundability" documented in the scientific literature.

In short, in the northern hemisphere, women are more likely to get pregnant in late fall and early winter than at other times of the year. As a result more births occur late summer and early autumn. In the southern hemisphere, the seasonal peak occurs about 6 months earlier.
Source: U.S. Centers for Disease Control and Prevention and author's calculations

You may note that the March births appear high, but consider that February is a short month, and March is a 31-day month. Similarly, the number of August births is nearly equal to that in September, but August is a longer month than September.

To correct for this, we can estimate the average number of births per day of the month.
Source: U.S. Centers for Disease Control and Prevention and author's calculations
With this adjustment the seasonal pattern becomes even more pronounced.