Where you live — in a city versus a rural area — could make a difference in how old you tend to be when you first have sex, what type of birth control you use and how many children you have.

These are the findings from federal data collected using the National Survey of Family Growth, which analyzed responses from in-person interviews with more than 10,000 U.S. women, ages 18 to 44, between 2011 and 2015.

On average, women living in rural areas said they had their first sexual encounter earlier than women living in urban areas, according to the survey. The mean age of first sexual intercourse among women living in rural areas was 16.6 years old. For women living in urban areas, the average age of first intercourse was 17.4.

That difference of less than a year isn't really what's most striking about the survey results, says Dr. Eleanor Bimla Schwarz, a research epidemiologist who specializes in women's health at the University of California, Davis, and wasn't involved in the survey. Rather, she says, it's that "sexual activity is a lot younger than a lot of people like to imagine it is in their own home — despite a more conservative and church-going environment in many rural areas."

By age 18, nearly 80 percent of women living in rural areas reported having experienced sexual intercourse, and 68.6 percent of women in cities.

When it comes to heterosexual marriage and cohabitation, there was no significant difference between women in urban and rural areas — about 40 percent of women in all regions surveyed were currently married to a member of the opposite sex. And the percentages who said they were living with an opposite-sex mate without being married were also very similar — 15.7 pecent for urban women and 18.6 percent for rural women. (The study didn't report data on non-heterosexual relationships.)

The survey did point up rural vs. urban differences in the number of children the women had. More women in the survey who were living in cities had no children (around 41 percent) compared to women living in rural areas (roughly 30 percent). And about 5 percent more women in rural areas had two or more children compared to urbanites.

When asked about contraception, one in five women in both groups reported they'd had sexual intercourse without using contraception. And, notably, more women in urban areas reported using less effective birth control methods to prevent pregnancy (a condom or withdrawal, for example) than their rural counterparts, who were more likely to use one of the most effective contraceptive methods — an IUD or sterilization.

Schwarz questions lumping IUDs — a readily reversible form of birth control — in the same category as sterilization.

"The real issue is that reversible and highly effective methods of birth control are less available to rural women than they are to urban women," she says, which may partly explain why more rural women choose sterilization as their method of birth control.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.