高房价是最好的避孕药
“高房价是最好的避孕药。”
这个段子显然只是一句玩笑，但是房价太高，真的会影响年轻夫妇的生育意愿吗？不敢要小孩，真的只是因为买不起房吗？
对于这种说法，人们往往有着自己的主观认识，但一直以来缺少足够数量的样本进行统计验证。
2018年6月，美国最大的房产平台Zillow发布的一份研究报告证实：房价和生育率之间存在着极强的负相关！
英文原文：Birth Rates Dropped Most in Counties Where Home Values Grew Most
这份报告指出：以全美国25-29岁妇女为样本，房价平均每上升10%，生育率就下降1.5%。并且在洛杉矶、西雅图、纽约这样的大城市，高房价对生育率的影响表现得更加明显。
“长安居大不易”，在生活成本本来就高的大城市，年轻夫妇的生育积极性更容易受到房价的影响。
根据芝加哥论坛报的一份问卷调查，82%的受访者将生育率下降归结为“财务因素”。
如果要养育小孩，全家势必要换到面积更大的住宅，而换房的成本对美国很多年轻家庭来说，已经成了“不可承受之重”。
1、房价每涨10%，生育率跌1.5%
Zillow研究机构分析师塔尔科，根据该公司2017年美国住宅市场报告和美国疾控中心提供的各郡县人口数据资料，进行了统计学分析。
从房价走势来看，美国西北部和西南部的住宅价格上涨幅度要远远超过中西部和东部：
西雅图去年的房价涨幅约12.5%
加利福尼亚州旧金山涨幅约为9.5%
德克萨斯州达拉斯涨幅达9.3%
拉斯维加斯涨幅更是达到14.3%
从人口出生数据来看，房价涨幅较大的区域，生育率下降得也更快。
以2010年到2016年时间段考察年轻妇女（25-29岁）生育率的话，美国西南部的加利福尼亚和德克萨斯两个人口大州生育率也下降得最多：
德州州府奥斯汀所辖郡县生育率下跌22%，加州的洛杉矶、圣迭戈等地生育率也普遍下降超过16%。
此外，美国西北部的西雅图所辖郡县生育率也大跌18%。
综合全美各地情况，房价（横轴代表）和生育率（纵轴代表）之间的统计学相关性极强：一个郡县的房价平均每上升10个百分点，当地生育率就下降1.5个百分点。
报告还发现，在纽约、洛杉矶、西雅图、芝加哥等大城市，在房价涨幅一定的前提下，年轻妇女生育意愿的下降程度要超过乡村地区。
2、生育意愿可能与多种因素相关
Zillow报告显示，在2010年到2013年间美国人平均初次购房年龄为32.5岁；随着房价的上涨，到了2017年平均初次购房年龄提高到了35.7岁。
与此同时，妇女选择生育的时间也在推迟：2010年，美国初为人母时的平均年龄为27.7岁，到2017年美国年轻妇女选择做母亲的平均年龄推迟到28.7岁。
那么，买不起房和不敢要小孩之间，到底有什么关联？
芝加哥论坛报的一份问卷调查显示，受访者不敢要小孩的最主要原因是财务方面的顾虑：有82%的受访者担心生小孩以后在财务支出上捉襟见肘，相比之下只有80%的受访者担心两人在感情还没完全稳固时就草率决定要小孩。
Zillow 报告指出，生育小孩需要考虑到的支出包括产假以外的旷工、抚养小孩的保育费用以及全家需要更大居住空间带来的换房支出。其中，住房需求是最大的一块开支。
当然，统计学上的强关联性并不等于必然的因果联系，也有专家在为美国惨淡的生育率寻找房价以外的解释原因。
美国人口学家克拉克认为，对职业生涯的考量和收入水平是影响年轻夫妇生育意愿的关键。
克拉克认为，在事业上更富有进取心的年轻人更容易聚集到房价高、就业机会多、商业网络发达的大城市。
这些年轻人生活在大城市里拥挤的租房空间，时间精力被职场占据，自然生育意愿较低。
马里兰大学一项研究表明，人群“用脚投票”的选择也造成城乡之间生育率的分化：呆在大城市里的年轻富裕人群普遍拥有较高的教育背景、社会地位，生育意愿较低；而有计划生育的年轻夫妇可能会选择搬到自然环境更好、住房价格更便宜、居住面积更大的郊区或者乡下，这样拉高了这些地方的生育率。
3、美国人担忧：生育率未见复苏
众所周知，2.1的生育率是理想的自然替代率，即平均每个妇女生育2.1名小孩，社会整体才能保持人口结构的平稳交替（不考虑移民因素）。
根据美国社会调查问卷（GSC），当被问到理想的家庭人数规模时，美国人给出的平均回答是生育2.6个小孩。
不过理想丰满，现实骨感。希望多生多养的美国人却在金融危机爆发之后生育率大幅下降，更令人担心的是，近几年来美国经济复苏的势头也没能拉升越走越低的生育率。
2007年，美国生育率数字为2.12，达到了理想水准。不过随着经济滑坡，美国妇女的生育率在2010年已经降到1.93。
2015年至今，美国经济开始展现强劲的复苏趋势，但生育率却还是一路向下：
2015年美国妇女生育率为1.84；2016年这个数字为1.82；2017年美国生育率已经掉到1.76，远远低于理想替代率。
据美国公共广播电台NPR报道，根据2018年5月的最新统计，美国生育率已经略低于1.76，降至30年新低。
美国经济学家林恩表示，由于社会政策没有充分支持美国妇女的生育计划，持续下降的生育率也将反过来损害美国经济的长期前景。
Birth Rates Dropped Most in Counties Where Home Values Grew Most（英文原文）
By Jeff Tucker on Jun. 6, 2018
- A recent decline in fertility was sharpest in counties where home values rose the most, and the change was smaller—and sometimes even up —where home value growth was weaker.
- An extra 10 percentage-point rise in home values was associated with an extra 1.5 percentage-point drop in birth rates for 25- to 29-year-old women.
- Even after accounting for the effect of home price increases, the West and Northeast still had bigger declines in fertility than the South and Midwest.
- Between 2010 and 2013, the average age of a first-time home buyer was 32.5, and as homes grew more expensive, that average age rose to 35.2 by 2017. Meanwhile, the average age of mothers at birth rose from 27.7 in 2010 to 28.7 in 2016.
The economic recovery produced a sharp rise in home prices from 2010 to 2016, and a simultaneous drop in the birth rate. The trends might be related (which is not to say causal), especially for women in their late 20s: Birth rates fell the most in counties where home values grew the most, and birth rates fell less and sometimes even increased in counties with smaller home price increases.
Economic Recovery, But No Baby Recovery
The U.S. baby bust started at the onset of the Great Recession in 2008, when the total fertility rate began falling. It dropped from a high of 2.12 per woman in 2007 to 1.93 by 2010.
Most observers expected that fertility would rebound as the economy recovered, but instead the fertility rate has continued falling. In 2016, the most recent year with detailed birth records, the total fertility rate was down to 1.82, andpreliminary data show it dropped to 1.76 in 2017.
A fertility rate of 2.1 births per woman is called the “replacement rate,” because it would maintain the population at a steady level without migration. The long-term effect of total fertility below 2.1 is for the population to steadily decrease.
The dropping birth rate could reflect changing family preferences. But the General Social Survey, which asks Americans, “What do you think is the ideal number of children for a family to have?”, showed a slight increase in the average response to that question, from 2.5 in 2010 to 2.6 in 2016. The Centers for Disease Control and Prevention (CDC)’s National Survey of Family Growth found that women continue to self-report (in 2002, 2010 and 2015) that they expect to have 2.3 children in their lifetimes and men continue to report expecting 2.2 children.
The Role of Home Values
Why might births be dropping? Raising a child is an expensive proposition, so it is little surprise that the most commonly given reason for delaying childbirth in a recent survey was the desire “to be financially established” first, cited by 82 percent of respondents.
Some challenges to financial stability when having a baby include the potential lack of paid parental leave, the cost of child care, and the cost of housing, if families need more space or want to buy a home before having a baby. Housing expenses were the single largest expense category, and the fastest growing, among the costs of child-rearing, according to a 2015 report by the United States Department of Agriculture. Home values have continued to rise since that report was issued, and the cost of housing likely became more daunting for many couples considering a child, especially if they did not already own a house before homes began appreciating so quickly.
The age group most likely to consider having a baby but not already own a home is 25- to 29-year-olds. Between 2010 and 2013, the average age of a first-time home buyer was 32.5, and as homes grew more expensive, that average age rose to 35.2 by 2017. Meanwhile, the average age of mothers at birth rose from 27.7 in 2010 to 28.7 in 2016. For these reasons, this analysis will focus on birth rates for women in their late twenties, which also controls for any changes in counties’ age composition over time.
If rising home values contributed to fewer babies being born, we would expect to see that birth rates fell more in places where home values rose more. Birth records from the CDC’s National Center for Health Statistics show that this is, in fact, what happened: There was a strong negative relationship between home value growth and birth rate change across large counties in the U.S. for 25- to 29-year-old women, from 2010 to 2016:
On average, if a county’s home value increase was 10 percentage points higher than another county’s, its fertility rate fell 1.5 percentage points further. For example, Fairfax County, Va., a large county in the suburbs of Washington, D.C., was near average on both dimensions: home values rose 17 percent, and fertility fell 8.2 percent. By comparison, in Monterey County, Calif., outside San Jose, home values rose 37 percent, and fertility fell 11.7 percent, or 3.5 percentage points more than in Fairfax County, similar to the 3.1 percentage point fall predicted by the model.
These results are especially driven by urban counties in the West and Northeast. For instance, Los Angeles County’s birth rate among 25- to 29-year-olds fell 16.8 percent as their home prices rose 31 percent. New York County (Manhattan) had the second biggest fertility decline in the Northeast– 20 percent — and the greatest home price increase in the region — 52 percent. Even after accounting for the effect of home value increases, the West and Northeast still had bigger declines in fertility than the South and Midwest.
Bucking the Trend in the Southwest
Some counties’ fertility changes fall well outside this trend line. The counties where births grew by more than home values predicted they would are in the South and Southwest, as Texas’s booming cities and sunny Southwestern counties bucked the trend despite their rising home values:
Meanwhile, the counties where births fell by even more than the trend in home prices would predict tended to be in large coastal cities or their suburbs, primarily in the West or Northeast:
The negative relationship between the two trends across counties is statistically significant, but clearly there is a great deal of variation in fertility declines unrelated to home values. Large differences from the trend reflect the fact that only 19 percent of the variation in fertility changes can be predicted by home value changes.
As a further caveat, the correlation observed here is by no means proof that home value growth causes fertility declines. One alternative explanation could be the possibility that there is clustering into certain counties of people with careers that pay well enough for expensive homes but make it difficult to have children before 30; this could cause both trends observed in the chart above. There are many other confounding factors that could explain this relationship as well, such as the possibility that cultural values or the cost of child care varies across counties with some correlation to home values.
Diverging Paths
Counties with the largest home value increases had exceptionally large drops in fertility. Those places in the top 20 percent for home value changes saw late-20s fertility drop by about 13 percent from 2010 to 2016, about twice as much as it fell in counties with medium home value growth. And this chart reveals that earlier in the economic recovery, through 2014, it was counties with the highest and the lowest value changes where fertility fell the most:
Looking ahead
The big question about post-recession birth rates is whether millennials are simply delaying childbirth or actually reducing the total number of births over their lifetimes compared to previous generations. Birth rates had been rising for women aged 30 and older through 2016, but provisional 2017 data released this May show that the fertility rates for 30- to 39-year old women reversed course last year and dropped for the first time since 2010.
On the other hand, the nationwide homeownership rate rose in 2017 for the first time since 2004, led by under-35 households – which could indicate that their next step is to have children. Meanwhile, the Zillow Home Value Forecast predicts home values will slow the pace of their gains, from the 8.7 percent observed in the last year to 6.5 percent over the next 12 months. It remains to be seen if these changes will help slow or reverse the fertility decline of the past ten years.
Methodology:
This analysis relied on the Zillow Home Value Index (ZHVI), and age-specific fertility rates from the Centers for Disease Control and Prevention’s National Center for Health Statistics. Counties with fewer than 10,000 women were excluded from the regression to reduce noise. Several different specifications were tested for robustness and yielded similar results.
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