Biomedical subjects
Publications and source records attributed to J R Udry.
An attempt was made to predict alcohol use among 101 American white boys aged 13-16. The model combined genetic and social variables. The analysis revealed evidence of a genotype-environment interaction and thus the use of either the biological or social variables alone poorly predicts alcohol use.
Previous studies of the seasonality of pregnancy and birth have typically been based on monthly numbers or proportions of pregnancies or births (i.e. their distribution throughout the year) without any explicit accounting of the size of the population actually at risk of pregnancy by month. From data on monthly populations at risk and monthly probabilities of pregnancy this paper determines the relative contribution of each component to the monthly distribution of pregnancies. The data come from the National Survey of Family Growth, Cycle III. While there is some seasonality in the size of the at-risk population, it contributes little to the overall monthly variation of pregnancy, which is determined mainly by seasonality of pregnancy probability (fecundability).
In this study we use serum steroid hormone assays and Adjective Check List responses from a representative sample of 102 male and 99 female adolescents to examine the relations between hormones, personality, and sexual behavior. We address two questions: (a) Does pubertal testosterone (T) cause sex dimorphism in personality? (b) Do pubertal hormones affect sexual behavior indirectly through effects on personality? Exploratory factor analysis of the Adjective Check List generated a factor common to male and female adolescents that correlated highly with T. However, male and female subjects did not differ in their mean level on this factor or in the correlation of this factor with T. In spite of the large sex difference in T, the girls were much more sensitive than the boys on the extracted factor to differences in T. We conclude that the answer to both questions is probably no.
The purpose of the study was to attempt to replicate a finding of Persky et al. (1978) that midcycle peak values of testosterone (T) in women predicted differences in frequency of intercourse among married couples. Luteinizing hormone (LH), total testosterone (TT), and free testosterone (FT) values from 10 to 14 daily midcycle blood samples donated by 43 volunteering wives were analyzed against sexual activity patterns reported by the couples over a longer period of time. All couples were contracepting by means other than exogenous hormones or the rhythm method. Each morning through three menstrual cycles husbands and wives recorded independently and on separate forms answers to a series of questions concerning sexual activity in the previous 24 hr. Wives also recorded basal body temperatures (BBT). We designated midcycle values of TT and FT according to several definitions of midcycle. Total testosterone levels at the day of the BBT nadir and the day before the nadir correlated significantly with average intercourse frequency. Correlations with FT were statistically significant regardless of which midcycle measure was used; the day before the BBT nadir gave the highest correlation, 0.618, p = 0.01. Mean testosterone (TT or FT) values were not significantly related. We conclude that female midcycle total testosterone or free testosterone is indexing some unobserved event that affects the frequency of intercourse of couples. We speculate that this event affects the motivation of females, which influences the set point of the compromise frequency characteristic of couples.
Twenty-five married women who were not using contraceptives provided daily urine specimens and coital reports for at least 90 days. The authors used urinary luteinizing hormone (LH) as a hormonal marker to determine ovulatory phase, onset of LH surge day, and LH peak day. Coital rate was elevated during the ovulatory phase of the menstrual cycle. Peak coital rate (0.72) occurred on onset of LH surge day, and was significantly greater (P less than 0.05) than the mean rate (0.44 +/- 0.06) across the entire menstrual cycle. The authors discuss possible social and hormonal mechanisms that might underlie an ovulatory peak in coitus, as well as the relevance of their findings to current models of fecundability.
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There are substantial differences in fecundability among nine developing countries in different parts of the world. In addition, within countries, later age at marriage has a clear, positive, nonlinear effect on fecundability. Women with higher education and those with more educated husbands have higher fecundability. Urban residents have higher fecundability than rural. The higher fecundability of more recent cohorts is the most consistent observation. Since those variables most frequently shown to have inverse relationships to fertility show direct relationships to fecundability within populations, the role of fecundability as a proximate variable in models of the determinants of fertility requires further specification.
The incidence of oral sex in an adolescent population is discussed. More girls have either given or received oral-genital stimulation than have had intercourse. More boys have had intercourse than have either given or received oral-genital stimulation. Oral sex is more common than intercourse for females because they are more likely to have received oral-genital stimulation than to have either had intercourse or given oral-genital stimulation. For both sexes, fellatio is less common than is either intercourse or cunnilingus. For both sexes, oral sex is considerably more frequently reported than was the case in the Kinsey surveys.
As part of a longitudinal study of young adolescents, data were collected in 1980 on the non-coital and coital sexual experiences of male and female adolescents who ranged in age from 12 to 15 at the time of the initial contact. The follow-up data were collected two years later. Both a Guttman-scale analysis and a longitudinal analysis of these data indicate different sexual patterns between White and Black teens; Whites are more likely than Blacks to engage in a predictable series of non-coital behaviors for a period of time before their first intercourse experience. Of the sexual behaviors studied, the pre-coital experiences of Black teens were less predictable and often involved only necking. These differences in sexual norms offer a partial explanation for the different pregnancy rates between these two groups. They also suggest that sexual and contraceptive education and counseling need to be cognizant of these differences since pre-coital experience may function as both a mechanism to prolong abstinence and to promote a gradual acceptance of one's sexuality.
Using panel data from a junior high school system in an urban area of Florida, we examine whether adolescents' best same-sex and best opposite-sex friends' sexual intercourse behavior increases the likelihood that respondents who are virgins at round 1 will make the transition to intercourse between rounds of our study. We find no significant influence effects of friends of either sex for black males or females, or white males. In contrast, white females are influenced by the sexual behavior of both their best female friend and best male friend. A virgin white female whose best friends of both sexes were sexually experience at round 1 was almost certain to have sexual intercourse within the two years of our study.
In order to separate hormonal from social effects on adolescent male sexual behavior, serum hormone assays were performed and questionnaire data on sexual motivation and behavior were collected on a representative sample of 102 boys in grades 8, 9, and 10 of a public school system. Free testosterone was a strong predictor of sexual motivation and behavior, with no additional contribution of other hormones. Including measures of pubertal development and age (indexing the effects of social processes) indicated no additional effects. Free testosterone, therefore, appears to affect sexual motivation directly and does not work through the social interpretation of the accompanying pubertal development.
A random sample of adolescent girls, 13 to 16 years of age, were surveyed with multiple serum progesterone determinations. The presence of ovulation was correlated with various indexes of pubertal development, including a pubertal developmental index that was devised using a summation of developmental factors. There was a significant correlation of ovulation with breast development, pubic hair development, and with the developmental index.
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Criteria are specified for distinguishing one-decision from sequential-decision models of fertility. Sequential decisions are not demonstrated by parity-specific differences in fertility determinants. Sequential models must demonstrate the importance of unanticipated intervening events in changing fertility plans or fertility experience. They must demonstrate that the intervening events are not caused by the fertility. Two empirical tests are designed to determine which model best fits the data. One test predicts fertility plans, the other fertility events. Both tests provide some support for sequential models.
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Data collected in Colombia and Thailand in 1977 are used to "compare the employment and household characteristics of migrants before and after the move in order to assess the degree of change which accompanies migration. Moreover, these comparisons [are] made for migration streams between places at different levels in the urban hierarchy with the intention of determining within which streams the greatest transformations occur."