Emergent Changes in American Demography and Social Organization

Key Points

  • The American Family is changing in response to the pressures and opportunities facing young individuals.
  • Many children today are being raised by single parents, which is associated with a lower transmission of skills to succeeding generations.
  • Technological advances and public provision of social protection benefits appear to be contributing to the decline of the nuclear family.

Emergent Changes in American Demography and Social Organization

Introduction

The term “demographic change” has become almost synonymous with “population aging” today, but it is actually much broader and multidimensional. The term encompasses changes in marriage rates, mating patterns, divorce, and living arrangements; shifts in fertility choices and timing; changes in immigration; improvements in mortality rates; and shifts in health and wellness patterns (smoking, nutrition, and exercise), educational attainment, labor force participation, and retirement. These changes are infusing seemingly permanent transformations in the forms of social organization even at the most basic level of “the family.”

The form of social organization has been evolving during the postwar period. This is the process of family formation and dissolution driven by technological advancements and economic opportunities that induce changes in social organization and cultural norms. They are reflected in trends in social institutions that govern family formation and dissolution across successive age-cohorts: marriage rates, mating patterns across socioeconomic groups, divorce rates and patterns, out-of-wedlock births, and frequency of single-parenthood.

The dilution of family ties is likely to affect the degree of skill and knowledge transmission to the next generation of workers. It is now widely accepted among sociologists and economists that children raised by single parents are less likely to succeed academically, more prone to engage in riskier activities, and less likely to realize positive market outcomes during adulthood.1 Indeed, perceptions of worsening economic prospects for younger American generations are already provoking calls for the government to play a larger role in children’s upbringing and education, even during early childhood.

Economics of the Family

The family is the most basic social unit within which the young are nurtured into responsible and self-supporting adults. Family formation might be motivated by the “survival instinct” – the desire to preserve and extend one’s lineage. Traditionally, communities with strong family values have been associated with strong social cohesion, cultural identity, and economic progress.

The economic approach to analyzing social structures views families as a means for achieving individuals’ economic goals. The form of “the family” can only promote social cohesion and economic progress if it is best suited to fulfill the demands for various types of services and exchange that are mutually valued by the individuals in a family. Those exchanges include physical security, close community, insurance against future economic uncertainty, sustenance during old age, a nurturing environment for children, and the transfer of cognitive and non-cognitive skills to one’s offspring.2 All of these functions, accomplished through family formation, have help to preserve and extend the heredity of individuals for many centuries.

Under this view, for any form of social organization to survive, it must continue to effectively deliver the services that its constituents seek. Social organization through families survived for many millennia partly because it was the most efficient way of delivering the key services needed for survival, protection, material and spiritual advancement, and generational succession.

Then, does the observed trend toward fragmentation of the family as the main form of social organization mean that it has become less efficient at delivering those services? Alternatively, have other means of acquiring those services emerged and become stronger?

Long Run Trends

Family fragmentation has been ongoing for many decades in the United States. There are many and changing reasons for this phenomenon. Joint living within extended families was the norm in many agricultural communities because arduous domestic and farm work compelled considerable division of labor and interdependence among extended family members.

The post-Civil War industrialization, technological change, and globalization meant greater urbanization and worker mobility leading to the dissolution of extended families. But those changes also meant the erosion of family support systems that protected individuals from economic misfortunes such as job loss, disability, unanticipated longevity (without means of economic support), divorce, dependency, and widowhood.

Post-World-War-II technological advancements also reduced exertional requirements in domestic work and permitted greater control over the timing of childbirth. These changes have allowed women to enter market production, contributing to economic growth and a greater sense of self-determination.

But those technological changes also led to greater specialization and increased business cycle volatility. The experience of the Great Depression of the 1930s was a watershed event: It prompted rapid growth in the entitlement-welfare state with the enactment of Social Security. That legislation is often described as America's "social response" to counter increased economic uncertainties for all individuals.

Over time, growth in publicly provided social protections have appeared to further erode the need for intra-family, inter-gender, and inter-generational risk sharing through family based social structures. Today, federal and state social insurance programs exist to insure individuals against income losses from life and health contingencies, benefiting retirees, the disabled, survivors, dependents, divorcees, students, children, and the poor. While such expansions of public safety net programs pools risk across households, it has also reduced family dependencies and the need for securing such protections through the family.


Figure 1: Household Composition of People Ages 18 and Older

Source: Decennial Census and the Current Population Survey.


With rising divorce rates, younger individuals may consider marriage to be less secure and seek to insure economic autonomy and independence before marrying. In this process, younger generations may rationally consider marriage as a poor bargain. In contrast, bachelorhood may be associated with greater social and financial freedom as, indeed, many national surveys confirm.3 Finally, the decline in marriage as a functional social institution may become self-perpetuating as younger generations emulate their elders’ behavior of altering their marital status multiple times.

Recent Trends


Figure 2: Population Shares of Married Males and Females by Age: 1988, 2000, and 2012

Source: PWBM calculations from the Current Population Survey.


Family formation through marriage is declining. Figure 2 shows a steady decline in the frequency of married individuals in the population. For both males and females, the decline is consistent and significant across all adults under 60 years. The marriage frequency profile declines with age at older ages, but it has shifted upward over time as declining mortality reduced the incidence of widowhood during the last two decades. The marriage decline among younger adults appears to be consistent with increased control over the timing of childbirth and potentially changing cultural norms away from marriage as a prerequisite for parenthood. Whether marriages will become insignificant in the future remains an open question. More important, however, is the efficacy of emergent social structures in preparing younger generations to face future economic challenges.


Figure 3: Population Shares of Single Males and Females by Age: 1988, 2000, and 2012

Source: PWBM calculations from the Current Population Survey.


Figure 3 shows that today’s youth, on average, are also tying the knot much later in life than their counterparts in the past. In 1960, most women married at the age of 20 and men at 23. Today, however, women marry, on average, at the age of 27 and men at 29.4 As young adults marry, the age-specific percentage of single individuals declines rapidly so that singles make up just 10 percent of those in their mid-thirties. Figure 3 shows that the rate of decline by age of the share of singles is shallower in 2012 compared to 1988, especially at young ages. It means that rate of transition into married status has gradually slowed during the last two decades, mirroring the decline in marriage rates.


Figure 4: Female Single Parents in 2010: Ages 15-20

Source: PWBM calculations from the Current Population Survey, 2010.


Figure 4 shows that black and Hispanic households are substantially more likely to be headed by a single female. From 1890 to 1930, black men were more likely to be married than white men. By 1960, this trend reversed and the change gained momentum after 1980.5 A number of studies attempt to examine the cause of this change, ranging from a decline in manufacturing, inequality and changes in social norms.6

Family Settings for Today’s Children

Relative to the past, today’s children are more likely to be raised by a single parent. According to data from the U.S. Census Bureau, approximately 87 percent of children resided with both parents during 1960s. By 2008, that number declined to 64 percent. At the same time, the number of children born to unmarried women increased from 5 percent to 41 percent.

The frequency of single-headed families among today’s adults has increased compared to the past – a shift that is shared by all racial groups. As shown in Figure 5, about 80 percent of children reside in white dual-headed families and 40 percent among black dual-headed families. Between 50 and 60 percent of Hispanic and Asian and Other children reside in dual-headed families.


Figure 5: Age-Specific Shares of Children in Single-Headed Families

Source: PWBM calculations from the Current Population Survey, 1988, 2000, and 2012.


From 1990 to 2010, the largest decline in children raised in married families is among the groups categorized as Asian and Other. Interestingly, the ratio of single-without-children and single-parenthood has not significantly changed for this group, suggesting that this decline reflects reduced fertility among married females during the last two decades. Among all races, in general, more children are still raised among families with two parents rather than one.

Conclusion

Social organization via two-parent married families is on a downward trend. As a result, more children are being raised in single-parent families. These demographic changes hold important implications, not only for economic prosperity of younger generations; they also threaten to undermine social support systems for older generations. If recent trends in social organization continue and lead to slower productivity growth, government revenues and the financial base for public social protection programs such as Social Security, Medicare, Medicaid, and SSI may become seriously compromised.


  1. Sara McLanahan and Christine Percheski (2008), “Family Structure and the Reproduction of Inequalities.” Annual Review of Sociology (34): 257-276. David Autor and Melanie Wasserman (2013), “Wayward Sons: The Emerging Gender Gap in Labor Markets and Education.” Third Way, Washington, DC.  ↩

  2. Economist Gary Becker initiated the concept of “family economics” where family formation and childbearing could be explained in terms of economic choices. He argued that people tend to make family choices based on whether they can improve their own welfare.  ↩

  3. A Pew Research Center Survey asked respondents for their views on whether society is better off if people make marriage and having children a priority, or society is just as well off if people have priorities other than marriage and children. Some 46% of adults chose the first statement, while 50% chose the second. See: http://www.pewsocialtrends.org/2014/09/24/record-share-of-americans-have-never-married/#fn-19804-4 ↩

  4. U.S. Census Bureau, Current Population Survey, March and Annual Social and Economic Supplements, 2015 and earlier. See: https://www.census.gov/data/tables/time-series/demo/families/marital.html.  ↩

  5. See “Historical Marriage Trends from 1890 - 2010: A Focus on Race Differences.” Presentation by a U.S. Census statistical team (Diana B. Elliott, Kristy Krivickas, Matthew W. Brault, and Rose M. Kreide) at the Annual Meetings of the Population Association of America, San Francisco, CA, May 3 - 5, 2010.  ↩

  6. See, for example, Kathryn Edin and Maria Kefalas (2005). Promises I Can Keep. University of California Press.  ↩

,1960,1990,2008
Living with spouse & children,47,33,27
Living alone,6,12,14
Living with children no spouse,6,8,10
Age,1988,2000,2012
18,0.0059,0,0.005
19,0.0181,0.0105,0.0053
20,0.0473,0.0217,0.0144
21,0.0465,0.0389,0.0236
22,0.0872,0.0632,0.0341
23,0.1158,0.0994,0.0485
24,0.1579,0.1098,0.0788
25,0.177,0.1156,0.0955
26,0.2077,0.1697,0.1163
27,0.2254,0.1977,0.1422
28,0.25,0.2283,0.1564
29,0.277,0.2143,0.184
30,0.2632,0.2513,0.2163
31,0.2926,0.2537,0.2009
32,0.2927,0.2834,0.2319
33,0.2947,0.2642,0.2365
34,0.2892,0.2679,0.2417
35,0.3173,0.2946,0.2549
36,0.3264,0.2667,0.2629
37,0.3226,0.2788,0.2746
38,0.3204,0.293,0.2872
39,0.3161,0.3053,0.297
40,0.3598,0.2913,0.28
41,0.369,0.2917,0.2896
42,0.3696,0.3136,0.2952
43,0.3475,0.3241,0.2814
44,0.3615,0.3241,0.3069
45,0.3643,0.3396,0.295
46,0.3651,0.3172,0.2974
47,0.359,0.3263,0.3014
48,0.3613,0.3466,0.2982
49,0.3796,0.314,0.2905
50,0.3391,0.3771,0.304
51,0.3846,0.3669,0.3198
52,0.3925,0.3653,0.3204
53,0.37,0.3758,0.3317
54,0.4063,0.3719,0.3283
55,0.3878,0.3462,0.3286
56,0.4059,0.3413,0.3073
57,0.36,0.368,0.3209
58,0.4095,0.3364,0.3172
59,0.3654,0.3514,0.3425
60,0.3738,0.3585,0.3392
61,0.3838,0.3636,0.3314
62,0.3776,0.3824,0.3269
63,0.3714,0.3763,0.3072
64,0.3684,0.3478,0.3355
65,0.3663,0.3438,0.3571
66,0.3673,0.369,0.3333
67,0.3696,0.3523,0.3534
68,0.3765,0.3529,0.3613
69,0.3373,0.3452,0.3415
70,0.3086,0.3256,0.3426
71,0.3649,0.3494,0.3608
72,0.3194,0.3043,0.3529
73,0.3582,0.3117,0.3529
74,0.2951,0.3506,0.3125
75,0.3125,0.3117,0.3067
76,0.3091,0.2958,0.3333
77,0.2593,0.2857,0.3594
78,0.3182,0.2794,0.3065
79,0.2564,0.2857,0.3175
Age,1988,2000,2012
18,0.0296,0.0213,0.005
19,0.0542,0.0368,0.0107
20,0.0947,0.0543,0.0239
21,0.1221,0.0833,0.0425
22,0.1686,0.1149,0.078
23,0.1789,0.1404,0.0825
24,0.2263,0.1618,0.1182
25,0.2392,0.1908,0.1256
26,0.2609,0.2242,0.1628
27,0.2676,0.2442,0.1814
28,0.2885,0.2554,0.2227
29,0.3099,0.2667,0.2406
30,0.3026,0.2667,0.2308
31,0.2969,0.2935,0.2511
32,0.3122,0.2995,0.2657
33,0.3285,0.3005,0.2759
34,0.3235,0.3158,0.2607
35,0.3221,0.2991,0.2647
36,0.3109,0.3067,0.2887
37,0.3226,0.3186,0.2591
38,0.337,0.3116,0.2979
39,0.3563,0.3097,0.2871
40,0.3333,0.3,0.3
41,0.3571,0.3241,0.2941
42,0.3261,0.3227,0.3048
43,0.3546,0.3241,0.3266
44,0.3615,0.3194,0.3175
45,0.3429,0.3255,0.31
46,0.3571,0.3333,0.3179
47,0.3504,0.3421,0.3158
48,0.3613,0.3239,0.2982
49,0.3426,0.3372,0.319
50,0.3739,0.3371,0.3304
51,0.3654,0.3373,0.3153
52,0.3645,0.3234,0.3107
53,0.35,0.3248,0.3116
54,0.3646,0.3306,0.3182
55,0.3673,0.3308,0.319
56,0.3465,0.3492,0.3281
57,0.38,0.336,0.3155
58,0.3429,0.3455,0.328
59,0.3654,0.3514,0.3149
60,0.3551,0.3302,0.3041
61,0.3636,0.3232,0.3081
62,0.3367,0.3137,0.3141
63,0.3238,0.3226,0.3012
64,0.3263,0.3478,0.3158
65,0.3168,0.3125,0.3052
66,0.2959,0.2857,0.3083
67,0.3152,0.3068,0.2931
68,0.2941,0.2941,0.2857
69,0.3133,0.3095,0.3089
70,0.284,0.3023,0.2685
71,0.2703,0.2651,0.2784
72,0.25,0.2899,0.2941
73,0.2388,0.2727,0.2824
74,0.2459,0.2208,0.2875
75,0.2188,0.2597,0.32
76,0.1818,0.2394,0.2667
77,0.2037,0.2063,0.25
78,0.1591,0.2206,0.2581
79,0.2051,0.1786,0.2222
Age,1988,2000,2012
18,0.4556,0.4574,0.4677
19,0.4398,0.4263,0.4599
20,0.3905,0.3913,0.4211
21,0.3605,0.35,0.4057
22,0.2965,0.3218,0.3854
23,0.2526,0.2807,0.335
24,0.2211,0.2659,0.3103
25,0.1914,0.2312,0.2563
26,0.1643,0.1939,0.2419
27,0.1455,0.1686,0.2108
28,0.1442,0.1522,0.1896
29,0.1268,0.1476,0.1651
30,0.0965,0.1231,0.1442
31,0.1048,0.1045,0.1279
32,0.0878,0.107,0.1208
33,0.0773,0.0933,0.1084
34,0.0784,0.0909,0.109
35,0.0721,0.0982,0.1029
36,0.0777,0.0889,0.0928
37,0.0645,0.0885,0.1036
38,0.0718,0.0837,0.0957
39,0.069,0.1062,0.0891
40,0.0688,0.0957,0.09
41,0.0774,0.0972,0.1131
42,0.0942,0.1,0.1
43,0.078,0.0926,0.1106
44,0.0923,0.1019,0.1111
45,0.1071,0.0991,0.125
46,0.0952,0.1398,0.1231
47,0.1111,0.1105,0.134
48,0.1008,0.1364,0.1284
49,0.1019,0.1337,0.1333
50,0.113,0.1429,0.1498
51,0.1058,0.1361,0.1441
52,0.1121,0.1557,0.1602
53,0.12,0.172,0.1558
54,0.1146,0.1405,0.1566
55,0.1122,0.1462,0.1524
56,0.1287,0.1587,0.1667
57,0.14,0.152,0.1765
58,0.1429,0.1727,0.1774
59,0.1442,0.1712,0.1713
60,0.1495,0.1698,0.1871
61,0.1515,0.1717,0.1919
62,0.1735,0.1569,0.1987
63,0.2,0.172,0.2108
64,0.1895,0.1848,0.1974
65,0.2079,0.2083,0.1948
66,0.2143,0.2024,0.2083
67,0.2174,0.2045,0.2155
68,0.2353,0.2235,0.2269
69,0.253,0.2143,0.2114
70,0.284,0.2442,0.2407
71,0.2703,0.2771,0.2371
72,0.3056,0.2899,0.2353
73,0.3134,0.2727,0.2235
74,0.3443,0.3247,0.2625
75,0.3438,0.2857,0.2667
76,0.3636,0.338,0.28
77,0.4074,0.3651,0.3125
78,0.4318,0.3824,0.3226
79,0.4359,0.3929,0.3492
Age,1988,2000,2012
18,0.497,0.484,0.4826
19,0.4639,0.4895,0.4759
20,0.4201,0.462,0.5024
21,0.4128,0.45,0.4575
22,0.3953,0.4138,0.4195
23,0.3632,0.3626,0.432
24,0.3105,0.3353,0.3744
25,0.2967,0.3237,0.3819
26,0.2609,0.2848,0.3442
27,0.2441,0.2616,0.3039
28,0.1923,0.2228,0.2559
29,0.1831,0.1905,0.2264
30,0.1886,0.1949,0.2356
31,0.1703,0.1891,0.21
32,0.1463,0.1551,0.2029
33,0.1401,0.171,0.1773
34,0.1373,0.1388,0.1564
35,0.1394,0.1563,0.1716
36,0.1192,0.1556,0.1495
37,0.1129,0.1504,0.1451
38,0.1215,0.1349,0.1223
39,0.1092,0.1504,0.1337
40,0.0952,0.1478,0.165
41,0.0833,0.1435,0.1493
42,0.0942,0.1227,0.1667
43,0.1064,0.1528,0.1457
44,0.0846,0.1296,0.1481
45,0.0929,0.1321,0.155
46,0.0873,0.129,0.1487
47,0.0855,0.1316,0.1579
48,0.0924,0.1307,0.1697
49,0.1019,0.1453,0.1571
50,0.1043,0.1029,0.1542
51,0.0865,0.1065,0.1532
52,0.0841,0.1078,0.1505
53,0.09,0.0955,0.1457
54,0.0833,0.1074,0.1414
55,0.0918,0.1308,0.1429
56,0.0594,0.1111,0.1563
57,0.08,0.12,0.1604
58,0.0857,0.1091,0.1344
59,0.0769,0.0991,0.1436
60,0.0935,0.1132,0.1404
61,0.0707,0.101,0.1337
62,0.0918,0.098,0.1282
63,0.0762,0.0968,0.1506
64,0.0947,0.087,0.125
65,0.0891,0.1042,0.1169
66,0.0918,0.119,0.1167
67,0.0761,0.1023,0.1034
68,0.0824,0.1059,0.1092
69,0.0843,0.0952,0.1301
70,0.0988,0.093,0.1204
71,0.0946,0.0964,0.1031
72,0.1111,0.1014,0.1059
73,0.0746,0.1039,0.1059
74,0.0984,0.1039,0.1125
75,0.0938,0.1299,0.1067
76,0.1091,0.0986,0.0933
77,0.0926,0.127,0.0938
78,0.0909,0.1029,0.1129
79,0.1026,0.125,0.0952
Age,White,Black,Hispanic,Asian and other
15,0.001576044,,,
16,0.003016591,0.023730422,0.027358732,0.029398148
17,0.002097902,0.02722881,0.012233149,0.035944472
18,0.010479042,0.023076923,0.038957935,0.014883244
19,0.016640254,0.075739645,0.049818371,0.027427491
20,0.014035088,0.06713615,0.093124246,0.056435644
21,0.031723143,0.100107066,0.086454592,0.035748792
22,0.044299201,0.145659637,0.082930552,0.023148148
23,0.04719764,0.20705347,0.082317831,0.02739726
24,0.045812455,0.282475201,0.145537525,0.041081909
25,0.042887777,0.186239007,0.136509293,0.085660643
26,0.07032967,0.295584416,0.151015801,0.066056064
27,0.068278805,0.315470643,0.140032191,0.045051522
28,0.070200573,0.285328533,0.132834225,0.067830314
29,0.098414795,0.29281768,0.191118489,0.112899897
30,0.062043796,0.372690401,0.172354949,0.111938562
31,0.081464873,0.374146341,0.20546697,0.128923007
32,0.096875,0.337042925,0.190534576,0.067498726
33,0.091926459,0.378824672,0.203125,0.093785568
34,0.067460317,0.364864865,0.181500873,0.100164541
35,0.102222222,0.284880895,0.234911987,0.103749358
36,0.097003155,0.301369863,0.216073479,0.057001795
37,0.107340174,0.352,0.163298872,0.165622389
38,0.096571029,0.316205534,0.191605839,0.111225329
39,0.089214381,0.260781329,0.160633484,0.111315125
40,0.077464789,0.278593914,0.153148966,0.082675337
41,0.091029024,0.245989305,0.163646659,0.111579934
42,0.072924188,0.229982964,0.154011023,0.085651537
43,0.065017668,0.194329592,0.149184149,0.103651685
44,0.057525084,0.200708383,0.129359165,0.065910319
45,0.060569352,0.186402266,0.131380978,0.08221055
46,0.057613169,0.151731721,0.094308405,0.126056879
47,0.055919096,0.157090142,0.098926895,0.060145808
48,0.060058309,0.149939541,0.099927326,0.057617729
49,0.039906103,0.117111995,0.13571665,0.108553655
50,0.04020979,0.123311803,0.124691793,0.058359177
Age,1988,2000,2012
0,0.1258,0.1942,0.2143
1,0.1517,0.1912,0.2301
2,0.1301,0.1799,0.2035
3,0.1448,0.1765,0.2174
4,0.162,0.203,0.2288
5,0.1781,0.1929,0.2333
6,0.1931,0.2361,0.25
7,0.1781,0.2153,0.2479
8,0.2101,0.2069,0.2358
9,0.1825,0.2323,0.2439
10,0.1825,0.2179,0.2422
11,0.1805,0.2381,0.246
12,0.2,0.226,0.2558
13,0.2061,0.2238,0.2462
14,0.2093,0.2297,0.2846
15,0.1985,0.2381,0.2595
16,0.2081,0.2397,0.2759
17,0.2102,0.2288,0.2721
Age,1988,2000,2012
0,0.6341,0.5922,0.6617
1,0.5607,0.6372,0.5752
2,0.5147,0.5811,0.5833
3,0.602,0.5634,0.6636
4,0.5758,0.5909,0.6268
5,0.5234,0.5758,0.5953
6,0.5767,0.5951,0.654
7,0.54,0.6441,0.6283
8,0.6065,0.6383,0.6825
9,0.5632,0.6052,0.6382
10,0.5291,0.5679,0.6111
11,0.5344,0.5975,0.6282
12,0.5652,0.5442,0.6364
13,0.5445,0.5565,0.6571
14,0.5699,0.5929,0.6385
15,0.55,0.6096,0.578
16,0.5829,0.4493,0.5856
17,0.5849,0.5223,0.5822
Age,1988,2000,2012
0,0.3099,0.3271,0.4086
1,0.2776,0.3046,0.4284
2,0.3224,0.316,0.3989
3,0.3065,0.3123,0.3661
4,0.3351,0.2847,0.4144
5,0.3263,0.2864,0.3878
6,0.3468,0.3509,0.3972
7,0.289,0.306,0.3684
8,0.3727,0.2913,0.381
9,0.3396,0.3193,0.3698
10,0.3009,0.3221,0.401
11,0.2612,0.3515,0.3712
12,0.3599,0.3133,0.3984
13,0.3684,0.3642,0.397
14,0.3952,0.3511,0.4059
15,0.3206,0.3448,0.3906
16,0.327,0.3235,0.3993
17,0.2743,0.3244,0.376
Age,1988,2000,2012
0,0.1628,0.2647,0.2353
1,0.18,0.2382,0.282
2,0.2193,0.1938,0.2684
3,0.1527,0.2492,0.2735
4,0.1769,0.3465,0.2707
5,0.1458,0.2397,0.2574
6,0.1349,0.25,0.2521
7,0.1349,0.2705,0.2755
8,0.2343,0.2726,0.3017
9,0.1824,0.2846,0.2511
10,0.1891,0.267,0.2303
11,0.1745,0.3469,0.264
12,0.2651,0.1969,0.1854
13,0.2093,0.2425,0.2664
14,0.2652,0.3153,0.2812
15,0.3395,0.1837,0.2717
16,0.2799,0.3165,0.2812
17,0.3111,0.2346,0.2966