Thursday, June 30, 2011

Delaying the wedding bells

As June is the unofficial national wedding month, it seems appropriate to wrap up this month with some concluding thoughts on marriage trends.

Educational attainment levels for women are at an all-time high in the U.S. Today eight percent of the female population age 15-50 has a graduate degree, 18 percent has a bachelor's degree, and nearly 60 percent have at least some college education (up to and including bachelor's and graduate degrees).

The likelihood of being married is considerably lower for lower levels of educational attainment. Less than half of women with "some college" education were married in 2009. And only one quarter of women with a less-than-high-school education are married. On the other hand, nearly 60 percent of women with a bachelor's degree and nearly 70 percent of women with a graduate degree are married.

So why the big difference?

The staff at the U.S. Census Bureau suggest that marriage is becoming a characteristic of the economically advantaged:
As marriage rates have decreased and cohabitation has become more common, marriage has become more selective of adults who are better off socioeconomically and have more education.
However, marriage doesn't "select" people. People select marriage. So I offer a counter-argument that there is larger force at work. Perhaps marriage isn't simply becoming a tradition of the well-to-do. Perhaps as more women choose to go to college, they are delaying marriage, and thus don't enter the "married" category until they achieve at least a bachelor's degree.

Source data: U.S. Census Bureau, American Community Survey, 2005 and 2009

Saturday, June 18, 2011

Are men faster than women, or did they just get a head start?

I am working on the Gender Stratification lesson plan for an Intro to Sociology class I am teaching, and I came across the following piece of gender history:
Not until 1984 in Los Angeles would the women's marathon become a sanctioned Olympic event. Joan Benoit Samuelson, the winner, had attended high school in Maine, where women's track teams were not granted varsity status during her freshman and sophomore years. She won the 1975 state championship in the mile -- the longest distance a woman was allowed to run -- but because she insisted on practicing with the boys to improve her times, she was denied the school's most valuable athlete award. "That's when I said to myself, 'I'll show that coach -- I'm going to win an Olympic medal some day,' " Samuelson says. Nine years later she did.
NY Times (1996)

In the era of Title IX it is difficult to remember that less than a generation ago, women were not grated equal access to sports (not to mention certain educational or occupational opportunities). Improvements in gender equity since the 1960s have been rapid, but the effects of gender discrimination linger.

One of the most common excuses for excluding women from certain endeavors has always been that they are not as ______ as men (insert "strong," "fast," "smart," "tough," or any number of other adjectives here).

But are women really weaker or slower than men?

Or did they just get a late start?

Today's marathon world record, still held by Paula Radcliffe from the 2003 London Marathon, represents a pace that is equivalent to the fastest man on earth in the early 1960s. And while men's marathon times have remained (from a statistical perspective) roughly stable over the last century, dropping from 2:55 in 1909 to 2:03:59 in 2006, women's times have seen rapid improvement.

Comparatively speaking, men dropped about 50 minutes off of their record times (for an improvement of 29 percent over 100 years). During the same period women's record times dropped by more than three hours, for an improvement of 60 percent over the same 100 years.

Today the differential in men's and women's paces can be measured in seconds per mile, not minutes.

In 1980 only 10 percent of marathon runners were female. In 2009 the proportion reached 41 percent (data from Running USA). The share of women running in shorter races has risen even faster. In the half-marathon distance, women became the majority of runners in 2005.

And, perhaps most interestingly, women who enter ultra-marathons (any distance longer than 26.2 miles) have a substantially higher likelihood of completing the race than male entrants do.

So it is entirely possible that women can be just as fast as men, but got a late start in this game. Granted, there are runners who make a strong argument to the contrary by suggesting that over the last couple of decades the disparity in paces between men and women has remained roughly constant both in the marathon and in other distances.

This is one case where only time will tell.

Chart data source:
data compiled by author

Monday, June 13, 2011

Let the wedding bells ring

Anyone who has ever glanced at a bridal magazine or received a wedding invitation knows that June is usually the hottest month for weddings. So in honor of all the happy couples, let's take a look at marriage statistics.

Not surprisingly, destination wedding locations have the highest marriage rates (per 1,000 population). The current rate (40.9) in Nevada is more than five times higher than the national average (6.8), and Hawaii rings in at more than double (17.9) the national average.

Some of the lowest rates, on the other hand, are in and around the nation's capitol. (With a decade of congressional infidelity scandals, the low marriage rate in D.C. is probably no surprise to readers.)

Marriage rates have been falling nationwide for the past decade, from 8.2 in 2000 to 6.8 in 2009 (data from the CDC). Falling marriage rates are part of a long-term trend toward delayed marriage. The average age at first marriage back in 1956 was only age 20 for women (age 22 for men) and has risen to age 26 for women (28 for men) today.

In marriage rates, Nevada declined the most, dropping from 72.2 in 2000 to 40.9 in 2009, and falling by more than 50 percent from a 1990 level of 99 marriages per 1,000 population. (Maybe being married by Elvis at a drive-through chapels is losing it's appeal?)

However, divorce rates are also falling. In fact, the number of "long-lasting" marriages is starting to increase. Divorce rates peaked in the years following mid-1970s changes in divorce laws, but then leveled off and fell slightly. Some of this can be attributed to lower marriage rates (fewer marriages likely lead to fewer divorces), but some is likely a result of people waiting longer to get married in the first place.

Image Credits:
Charts by author, with data from the U.S. Centers for Disease Control and Prevention (CDC)
Photo courtesy of

Tuesday, June 7, 2011

Demographic trends in San Diego County – new data from Census 2010

Population Growth 1910-2010
In the past 100 years, San Diego county has grown from a small city of 60,000 people to a thriving metropolitan area of more than 3 million. In San Diego’s early years Census figures show that the county’s population nearly doubled every ten years from 1910 to 1960. Between 1960 and 1990 growth slowed to an average increase of approximately 33 percent every decade. Growth slowed again in recent years, with less than a 15 percent increase 1990-2000 and only 10 percent growth from 2000-2010.

Migration Patterns
Migration was the primary driver of population growth at the beginning of the last century, but that trend has shifted considerably in recent decades. Until the late 1990s, most growth in Southern California was a result of in-migration from other parts of the United States and from other countries around the world.

However, according to data from the U.S. Census Bureau American Community Survey and a study by the University of Southern California Population Dynamics Research Group, that trend has shifted statewide, with most of the population now being, in the words of the study authors, “homegrown” (i.e. born in California).

Aging Population
As San Diego grows, it is growing older. The very first trickle in the aging wave of the Baby Boomers just turned 65 this past January. Because the Baby Boom is just now reaching this milestone, the proportion of the population age 65 and older had remained constant at 11 percent over the past two decades. However, that will shift dramatically in the next two decades.

On the younger end of the spectrum, the share of San Diego's population under the age of 18 is shrinking, from 26 percent in 2000 to 23 percent in 2010. As a result of these shifts the median age (the point at which half of the population is younger and half older) increased from 31.0 years in 1990 to 34.6 today.

Race and Ethnicity
One of the biggest demographic shifts highlighted by the 2010 Census is confirmation that San Diego is now a “majority-minority” county. This means that no single race or ethnic group accounts for more than half of the region’s population.

The Asian population, which grew fastest, increased by 34 percent (to 328,000 residents) between 2000 and 2010. The Hispanic/Latino population increased by 32 percent over the decade, and now accounts for approximately one third of the county’s total population (991,000 residents).

Conversely, the non-Hispanic White, Black, and American Indian populations all declined slightly during the decade (by 3, 5, and 8 percent, respectively)

Housing - Occupancy and Household Size
While much talk about the Census revolves around the demographic characteristics of the population, the 2010 Census also provides valuable information about neighborhood housing characteristics including occupancy rates and average household size.

In 1950, the average household size in San Diego was more than 3.1 persons per household. This decreased steadily as birth rates and average family size fell during the 1960s and 1970s, so by 1980, the region hit a low of 2.6 persons per household. However, birth rates began to rise starting in the mid-1970s, and a similar upward trend can be seen in average household size.
San Diego's lowest residential vacancy rates, not surprisingly, were during the housing boom in the early 2000s, and have risen considerably – back to rates reminiscent of the 1970s and 1980s – in the past three years. Data from the 2010 Census shows a residential vacancy rate of 6.7 percent for San Diego county.

2010 and Beyond
The demographic characteristics of the San Diego county will continue to evolve over time. San Diego is transitioning from a history of high-volume in-migration, to a more “homegrown” population, and from a relatively "young" area to a metropolitan area with an aging population.

Source data:
U.S. Census Bureau, Census 2010, Redistricting Files
California Department of Finance, Demographic Research Unit

Sunday, June 5, 2011

Aging population and driving

This story in today's San Diego Union Tribune, about a fatal accident involving a 71-year-old driver, prompted me to post a piece I've been working on for a couple of weeks...

Six months ago the first wave of Baby Boomers turned 65, prompting questions about how the nation's transportation system will adapt to an aging population. There are some benefits that may arise from having an older population, and there will undoubtedly be challenges.

As the population ages we may care less about our cars. A Gallup poll in 1991 found that 20 percent of Americans found driving to be a chore. The same response in 2006 got a 40 percent boost to 28 percent. When you drill down into the details of the survey, likelihood of taking a ride “just because it’s fun” decreases substantially with age. In short, an older population is less likely to enjoy driving.

And, contrary to most road-rage induced stereotypes, older Americans also drive more safely. (However, there are some limitations to that trend, as described below.)

In their 2009 study of aggressive driving behavior, AAA found that at age 16 nearly 60 percent of drivers show aggressive behavior. By age 35 aggressive driving falls to 35 percent and by age 60 is below 27 percent.

With an already aging population, safer driving is beginning to show up in accident statistics. According to the U.S. Department of Transportation:

“in 2010 the number of traffic fatalities in America fell to the lowest levels since 1949...despite a sharp increase in the number of miles Americans drove last year - 21 billion additional miles. In addition, the rate of road fatalities in the U.S. has also dropped to its lowest level since 1949. Over the last five years, traffic deaths have declined by 25 percent…And the rate of fatalities per million miles traveled fell to 1.09 from 1.13 in 2009.”

Transportation Secretary Ray LaHood credits this to “the combined efforts of DOT, states, law enforcement, safety organizations, and America's drivers who are taking personal responsibility for their driving habits.” But I also see a demographic shift at play, much as there was a demographic influence on falling crime rates, beginning in the mid-1990s.

However, as opening article implies, there are also substantial health issues that may impair the driving of older Americans.
For example, the likelihood of reporting some form of disability DOUBLES between the age groups 65-74 and 75 and older (from 25 percent at age 65 to fully half the population age 75+). Similarly, according to data from the U.S. Centers for Disease Control and Prevention 10 percent of older men and 15 percent of older women reported cutting back on driving due to a physical problem in the past year. And, for a combination of reasons, older drivers are likely to avoid driving in certain conditions. Older drivers tend to avoid driving at night, driving in bad weather, and (to a lesser extent) driving in heavy traffic.

All of this adds up to some very complicated issues facing the nation's transportation system. Fortunately, research is underway to better understand the implications of age-related health issues on transportation at institutes such as the Age Lab at MIT.

Saturday, June 4, 2011

Data vs. Information (round 2)

Convenient to this week's blog theme on "Data vs. Information", The Economist published a post by Joseph Schumpeter on the issue of rampant growth in data and what mountains of data mean for business decisions. The entire article is worth reading, but the following quote struck me as particularly well-written:

The sheer size of today’s data banks means that companies need to be more careful than ever to treat data as a slave rather than a master. There is no substitute for sound intuition and wise judgment. But if firms can preserve a little scepticism, they can surely squeeze important insights from the ever-growing store of data.

Wednesday, June 1, 2011

Hurricane seasons begins

It's June 1, so the 2011 hurricane season has begun...

Nearly 37 million people live in areas most at risk of hurricanes, an area covering 179,000 square miles along the coastal region stretching from Texas to North Carolina, according to the U.S. Census Bureau. Hurricanes occasionally strike farther north, but such events are rare.

Hurricane History
The Department of Housing and Urban Development estimates that in the summer of 2005 hurricanes Katrina, Rita, and Wilma damaged "more than one million housing units across five states." Of the damaged homes 515,000 were in Louisiana, 220,000 in Mississippi, and nearly 140,000 in Texas.

By 2010, according to the HUD study, three quarters of the 2005 hurricane-damaged properties on "significantly affected" blocks were in good condition (at least on the outside*), but nearly 15 percent of the properties still had substantial visible repair needs, and 11 percent no longer contained a permanent residential structure. Louisiana homes, of the state affected, are most likely to still have unrepaired damage. Mississippi homes were most likely to be either repaired or entirely demolished and left vacant.
*We should note that these estimates do not include homes with mold or other water damage issues that might render the structures uninhabitable.

From a business perspective, in the year following Katrina New Orleans had about 95,000 fewer jobs, with most losses in tourism and port operations. It took nearly two years after Katrina for the number of restaurants in New Orleans to rebound to it's pre-hurricane level (according to restaurant critic Tom Fitzmorris in his book Hungry Town).

Hurricane Demographics
In addition to their physical and economic damage, major hurricanes can cause huge demographic shifts. For example, during hurricane Katrina approximately 1.5 million people over the age of 16 left their homes in Louisiana, Mississippi, and Alabama. And while many have returned, not all have. For example between 2005 and 2010 New Orleans saw its population decline by 25 percent from an estimated 455,000 before the hurricane to 344,829 as of April 1, 2010.

And while New Orleans tends to dominate the news headlines because of the broken levees, Pass Christian, MS actually has sustained a greater proportionate loss in population. Though a small town before Katrina (just under 7,000 according to 2005 Census Bureau estimates) the population had shrunk in half in the year following the hurricane, and many residents did not return. The 2010 Census count shows a resident population of only 4,613 - a sustained decline of 34 percent since the hurricane. Gulfport, MS also declined by an estimated 5,500 residents (-8 percent) between 2005 and 2010.

Less notorious, but just as significant in terms of population shift, was Hurricane Ike in Galveston, TX. Nearly 10,000 residents remained displaced two years after the hurricane. The estimated population before Ike was 57,000 but was only 47,743 at the 2010 Census. The HUD report on housing shows that one quarter of homes in Texas hurricane-affected neighborhoods still showed significant damage in 2010, in part because of the 2005 series of hurricanes and in part because of Ike.

In natural disasters traditional sources of demographic data (building permits, school enrollment records, utility hookups, drivers licenses, etc...) are either no longer available, or provide misleading information about the displaced, remaining, and returning population. Some of the most clever demographic techniques I have seen to date were hurricane-related. At the 2010 Applied Demography conference Mark VanLandingham and Janna Knight presented their techniques for reverse-estimating the post-Katrina population of New Orleans. And Nazrul Hoque, Alelhie Valencia, and Karl Eschbach presented their techniques for filling in the data gaps for post-hurricane Galveston.

Hurricane Preparedness
And in case all this talk of hurricanes has you thinking it's time to update your emergency preparedness kit, the CDC has developed a useful but tongue-in-cheek checklist that will get you through any disaster - even a zombie apocalypse!Get A Kit,    Make A Plan, Be Prepared.
Click on image for more information from the CDC.

Image of Hurricane Katrina in the Gulf of Mexico courtesy of NASA-GSFC, data from NOAA GOES