Family size is largely a matter of choice, at least in Western countries. There are various indicators of family size, such as birth rate (births/1000 population/year) and fertility rate (children born/woman). Both measures vary widely across as well as within societies [1Kotkin J. The next hundred million. New York: Penguin Press 2010.]. For example, the fertility rate (as of 2014) is over 5 in many African countries; approximately 2 in the U.S.; less than 2 in Australia, Canada, Russia, and most of Europe; and close to 1 in many Asian countries [2CIA World Factbook. Country comparison: Total fertility rate. Available from: http://www.indexmundi.com/g/r.aspx?v=31 2014. Jan 1 [retrieved 2016 Dec 21]]. Use of birth control measures roughly parallels family size; countries (or racial/ethnic groups within countries) that have higher birth control utilization have correspondingly lower birth rates [3Balbo N, Billari FC, Mills M. Fertility in advanced societies: A review of research. Eur J Popul/Rev Eur de Démographie 2013; 29(1): 1-38.
[http://dx.doi.org/10.1007/s10680-012-9277-y] ].

Within a society, there are significant demographic differences. In the U.S., Whites have a lower birth rate than Blacks, Hispanics, and Asians [1Kotkin J. The next hundred million. New York: Penguin Press 2010., 4Martin JA, Hamilton BE, Osterman MJ, Curtin SC, Matthews TJ. Births: final data for 2013. Natl Vital Stat Rep 2015; 64(1): 1-65.
[PMID: 25603115] ]. With respect to religion, there is a widespread perception that Catholics tend to have large families, and to some extent, Catholics are more likely to view a larger family as ideal [5Nobbe CE, Okraku IO. Male-female differences in family size preferences among college students. Soc Biol 1974; 21(3): 279-89.
[http://dx.doi.org/10.1080/19485565.1974.9988122] [PMID: 4450120] -7Westoff CF, Potvin RH. College women and fertility values. Princeton, NJ: Princeton University Press 1967.
[http://dx.doi.org/10.1515/9781400876051] ]; yet religious differences in fertility are much less than in the past and are possibly now non-existent altogether, at least in the U.S [8Frejka T, Westoff CF. Religion, religiousness and fertility in the U.S. and in Europe. Paper presented at the 2006 annual meeting of the PAA (Los Angeles, CA 2006). Available from: http://www.d.umn.edu/~okuhlke/Fall%202006%20Classes/GEOG%203762%20Europe/ Readings/Week%2013%20-%20Demography/ EUdemogr1.pdf. 2006.].

Men and women likely make decisions about procreation quite differently, due to sex roles, family influences, and biology. For example, women’s fertility and family size preferences are related to their sex-role attitudes [9Granberg D. Family size preferences and sexual permissiveness as factors differentiating abortion activists. Soc Psychol Q 1982; 45: 15-23.
[http://dx.doi.org/10.2307/3033670] -11Wrigley AP, Stokes CS. Sex-role ideology, selected life plans, and family size preferences: Further evidence. J Comp Fam Stud 1977; 8: 391-400.]. A 2009 study found that females who intended to have children were significantly more likely to identify having a “biological” drive to have children compared to males who intended to have children and both males and females who did not intend to have children [12Landridge D, Sheeran P, Connolly K. Understanding the reasons for parenthood. J Reprod Infant Psychol 2005; 23(2): 121-33.
[http://dx.doi.org/10.1080/02646830500129438] ]. Consistent with this finding, a core tenet of sociobiological theory is that women should be more selective in mating than men, by virtue of their greater investment in terms of material and physiological resources [13Wilson EO. Sociobiology: The new synthesis (25th anniversary edition). Cambridge, MA: Harvard University Press 2000.]. There is evidence for this differential selectivity across the animal kingdom, including in humans [13Wilson EO. Sociobiology: The new synthesis (25th anniversary edition). Cambridge, MA: Harvard University Press 2000.].

Despite the clear relevance of family size to well-being and resource utilization, at both the micro (e.g., individual, clan) and macro (e.g., village, society) levels, surprisingly little research has addressed exactly how and when individuals decide how large a family to have. What research exists has focused primarily on married persons [6West KK, Morgan LA. Public perceptions of the ideal number of children for contemporary families. Popul Environ 1987; 9: 160-72.
[http://dx.doi.org/10.1007/BF01259306] , 14Beckman LJ. Fertility preferences and social exchange theory. J Appl Soc Psychol 1979; 9: 147-69.
[http://dx.doi.org/10.1111/j.1559-1816.1979.tb00801.x] -16Miller WB, Pasta DJ. Motivational and nonmotivational determinants of child-number desires. Popul Environ 1993; 15: 113-38.
[http://dx.doi.org/10.1007/BF02209405] ]; however, individuals appear to enter marriage with some expectations about childbearing and family size already formed [17Sabatello EF. Premarital experiences and family size expectations of U.S. Jewish women: Some exploratory comparisons. J Popul Stud 1985; 19: 149-56.]. Studies of older, married individuals are limited, moreover, by the fact that the strongest predictor of the number of children desired is the number of children one already has [16Miller WB, Pasta DJ. Motivational and nonmotivational determinants of child-number desires. Popul Environ 1993; 15: 113-38.
[http://dx.doi.org/10.1007/BF02209405] , 18Gwako E. Married women’s ideal family size preferences and family planning practices: Evidence from rural Kenya. Soc Sci J 1997; 34: 369-82.
[http://dx.doi.org/10.1016/S0362-3319(97)90035-5] ].

The scant research that has addressed the preferences of younger, single individuals has focused primarily on women [11Wrigley AP, Stokes CS. Sex-role ideology, selected life plans, and family size preferences: Further evidence. J Comp Fam Stud 1977; 8: 391-400.]. Some research has compared the family size preferences of young, unmarried men and women [5Nobbe CE, Okraku IO. Male-female differences in family size preferences among college students. Soc Biol 1974; 21(3): 279-89.
[http://dx.doi.org/10.1080/19485565.1974.9988122] [PMID: 4450120] ]. This research found that single women desired larger families than single men, a difference that it attributed to sex roles; however, most of the literature in the area is dated, and sex roles have changed considerably since the 1960s and early 1970s. For example, in 1970, 40% of women in the U.S. were employed in the labor force, compared to 56% in 2008 [19U.S. Department of Labor. Women in the labor force: A databook. Washington, DC: Bureau of Labor Statistics, 2009. Available from: http://www.bls.gov/cps/ wlf-databook-2009.pdf 2009.]. In addition, prior research has not addressed the age and processes by which family size preferences are formed. The present study addresses these gaps in the literature by examining family size preferences in a sample of childless male and female college students.

The data were analyzed using SPSS; degrees of freedom vary because participants had the option not to answer individual questions. All but seven participants indicated a desire for children, with a majority indicating a preference for two (33.9%) or three (35.2%) children (M = 3.08, SD = 1.59). Similarly, the average number of children in home of upbringing was around three (M = 3.02, SD = 1.28).

Table 1 shows the major findings. There was a marginally significant difference in the number of children desired by men (M = 3.28) and women (M = 2.94), t(267) = 1.92, p = .06, η² = .01. As hypothesized, women (M = 15.82) reported making a decision earlier in life about the number of children they wanted to have compared to their male counterparts (M = 17.55), t(348) = 5.10, p < .01, η² = .07. Women showed a higher degree of commitment (M = 4.92) than men (M = 4.56) to their desired number, t(346) = 2.37, p = .02, η² = .01.

Table 1
Desired number of children, age of decision, and degree of commitment as a function of demographic and behavioral characteristics.

Men and women differed significantly in their response to the question, “Was the decision something you thought through carefully or a gut feeling?” t(360) = 2.05, p < .05, η² = .01, with women more likely to have given the decision careful thought (Ms = 4.04 [SD = 1.45] vs. 3.72 [SD = 1.52]). Women wanted their first child at a significantly younger age (M = 26.05, SD = 2.11) than men (M = 26.61, SD = 2.78), t(352) = 2.18, p < .05, η² = .01, but there was no significant difference between women and men regarding the age at which they wanted to have their last child, t(341) = 1.91.

When asked how much regret they would experience if they had either more or fewer children than desired, men and women did not differ significantly, ts < 1.61. Participants predicted they would experience less regret over having more children (M = 2.39, SD = 1.50) compared to having fewer children than desired (M = 3.21, SD = 1.86), t(389) = 7.27, p < .01, η² = .12.

As an overwhelming majority of the participants identified as White (85.8%), ethnicity was coded as being either White or racial/ethnic minority. There was no significant difference in the number of children desired by Whites and minorities, t(393) = .42. Race/ethnicity also was unrelated to the age at which participants reported deciding on the number of children they wanted to have, t(377) = 1.17, or their degree of commitment, t(374) = .86.

Although data were collected for a variety of religious groups, participants predominantly identified as being Catholic (31.2%) or Protestant (56.4%). There was no significant difference in the number of children desired by Catholics and Protestants, t(349) = 1.04. Catholics and Protestants also did not differ on the age at which they reported deciding on the number of children they wanted to have, t(335) = 1.44. Catholics and Protestants showed a small (η² = .02) but significant difference in how committed they were to the number of children they wanted to have, with Catholics less committed (M = 4.55) than Protestants (M = 4.96), t(334) = 2.55, p = .01.

Over half of the participants (57.9%) indicated that they had been sexually active in the past 6 months. Of these, 95% were using some form of birth control (BC). One’s decision to use BC may reflect childbearing intentions, but because of the small number of non-BC users, these analyses are exploratory. There was a small (η² = .03) but significant difference in the number of children desired by BC users (M = 2.94) and non-BC users (M = 4.10), t(230) = 2.45, p = .02. BC users and nonusers did not differ on the age at which they reported deciding on the number of children they wanted to have, t(222) = 1.26, or their level of commitment, t(222) = .00.

The vast majority of participants desired children, which is consistent with both biological imperatives and gender roles for both men and women [13Wilson EO. Sociobiology: The new synthesis (25th anniversary edition). Cambridge, MA: Harvard University Press 2000.]. The number desired by most participants—two or three—is a robust finding in recent American samples [6West KK, Morgan LA. Public perceptions of the ideal number of children for contemporary families. Popul Environ 1987; 9: 160-72.
[http://dx.doi.org/10.1007/BF01259306] , 11Wrigley AP, Stokes CS. Sex-role ideology, selected life plans, and family size preferences: Further evidence. J Comp Fam Stud 1977; 8: 391-400., 20Hagewen KJ, Morgan SP. Intended and ideal family size in the United States, 1970–2002. Popul Dev Rev 2005; 31(3): 507-27.
[http://dx.doi.org/10.1111/j.1728-4457.2005.00081.x] [PMID: 20376334] ] and consistent with the current U.S. fertility rate [1Kotkin J. The next hundred million. New York: Penguin Press 2010., 2CIA World Factbook. Country comparison: Total fertility rate. Available from: http://www.indexmundi.com/g/r.aspx?v=31 2014. Jan 1 [retrieved 2016 Dec 21]]. Even though most participants were in their late teens or early twenties, nearly all had a specific number of children in mind, and they tended to be strongly committed to that number (the mean score on the commitment question was above the midpoint for both men and women). Nonetheless, there were some significant differences in terms of demographic characteristics, especially as a function of participants’ gender.

Women reported deciding how many children they wanted at a younger age than men, by nearly two years. Women also reported being more firmly committed to a specific number, desiring slightly fewer children than men on average, and wanting to have their first child at a younger age. The gender difference in number of desired children contradicts a previous research finding that women preferred slightly more children than men [5Nobbe CE, Okraku IO. Male-female differences in family size preferences among college students. Soc Biol 1974; 21(3): 279-89.
[http://dx.doi.org/10.1080/19485565.1974.9988122] [PMID: 4450120] ]. A likely explanation of this discrepancy is societal changes over time. The research reviewed by Nobbe and Okraku [5Nobbe CE, Okraku IO. Male-female differences in family size preferences among college students. Soc Biol 1974; 21(3): 279-89.
[http://dx.doi.org/10.1080/19485565.1974.9988122] [PMID: 4450120] ] was conducted in the 1960s and early 1970s, at the beginning of the women’s liberation movement in the U.S. Since that time, many more women have entered the workforce, as traditional sex roles have relaxed; and working women, as well as those with less traditional sex-role attitudes, desire fewer children [14Beckman LJ. Fertility preferences and social exchange theory. J Appl Soc Psychol 1979; 9: 147-69.
[http://dx.doi.org/10.1111/j.1559-1816.1979.tb00801.x] , 15Beckman LJ. The relationship between sex roles, fertility, and family size preferences. Psychol Women Q 1979; 4(1): 43-6.
[http://dx.doi.org/10.1111/j.1471-6402.1979.tb00698.x] [PMID: 12336874] , 21Kaufman G. Do gender role attitudes matter? Family formation and dissolution among traditional and egalitarian men and women. J Fam Issues 2000; 21(1): 128-44.
[http://dx.doi.org/10.1177/019251300021001006] ]. These trends likely contribute to the closing, and even reversal, of the male-female gap in family size preferences.

Both men and women anticipated experiencing more regret at having too few than too many children. This tendency could reflect a framing effect, whereby “too few” involves imagining taking away something one already has, which is perceived as a loss [22Kahneman D, Tversky A. Prospect theory: An analysis of decision under risk. Econometrica 1979; 47: 263-91.
[http://dx.doi.org/10.2307/1914185] ]. Of course, participants did not already have children, but in their imagined subjective future state, it would nonetheless be perceived as a loss, compared to the incremental “gain” of having more children than desired [23Beach LR. Image theory: Theoretical and empirical foundations. Mahwah, NJ: Lawrence Erlbaum Associates 1998.].

Participants who used birth control wanted fewer children than participants who did not. This finding is consistent with other research showing that the availability of family planning measures is associated with intentions to have fewer children [18Gwako E. Married women’s ideal family size preferences and family planning practices: Evidence from rural Kenya. Soc Sci J 1997; 34: 369-82.
[http://dx.doi.org/10.1016/S0362-3319(97)90035-5] , 24Bongaarts J. Fertility and reproductive preferences in post-transitional societies. Popul Dev Rev 2001; 27: 260-81.]. A variety of factors go into the decision whether to use birth control [25Philliber S, Namerow PB, Kaye JW, Kunkes CH. Pregnancy risk taking among adolescents. J Adolesc Res 1986; 1: 463-81.
[http://dx.doi.org/10.1177/074355488614011] ]. Contraceptive use and family size preferences are likely part of a constellation of variables including sex-role attitudes, career aspirations, and other factors [12Landridge D, Sheeran P, Connolly K. Understanding the reasons for parenthood. J Reprod Infant Psychol 2005; 23(2): 121-33.
[http://dx.doi.org/10.1080/02646830500129438] , 14Beckman LJ. Fertility preferences and social exchange theory. J Appl Soc Psychol 1979; 9: 147-69.
[http://dx.doi.org/10.1111/j.1559-1816.1979.tb00801.x] , 15Beckman LJ. The relationship between sex roles, fertility, and family size preferences. Psychol Women Q 1979; 4(1): 43-6.
[http://dx.doi.org/10.1111/j.1471-6402.1979.tb00698.x] [PMID: 12336874] ]. Contraceptives allow women (and their partners) to be more selective about when they want offspring and how many of them to have [6West KK, Morgan LA. Public perceptions of the ideal number of children for contemporary families. Popul Environ 1987; 9: 160-72.
[http://dx.doi.org/10.1007/BF01259306] ].

Overall, college students’ family size preferences were consistent with sociobiological predictions. Women reported deciding how many children they wanted at a younger age than men, being more committed to a specific number, having given the matter more careful thought, and wanting to start childbearing at a younger age. Thus, despite recent cultural and societal changes, biological imperatives still appear to influence decision making about this most fundamental of behaviors.