```help birthsim
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Title

birthsim --  Simulate completed fertility and birth intervals

Syntax

birthsim [,startyear(real 2000) endyear(real 2100) birthday(real 5)
birthmonth(real 5) birthyear(real 1985) marriageday(real 5)
marriagemonth(real 5) marriageyear(real 2005)
latestageatbirth(real 50) probabilityconceive(real .2)
contraceptioneffectiveness(real 0)
probabilitymiscarriage(real .25) fetallossinfertility(real
4) monthsofpostpartum(real 12)]

Description

birthsim simulates birth intervals and number of children born according to inp
> utted parameters. Calculations
are based on Preston, Heuvaline, and Guillot (2001). It creates a column of liv
> ed months, with values
for months that resulted in a conception. From this data it is also easy to cal
> culate respective birthdays
and ages of the simulated offspring. To obtain a statistical range of births gi
> ven the parameters,
simulate the process multiple times using the simulate command as shown in the
> example below.

Parameters/Options

{probabilityconceive} This is the probability that the sexually active
woman will conceive in any given month.  The default value is set to
.2, which is average (Preston, Heuvaline, and Guillot 2001).

{latestageatconception} This is the latest age at which the woman will
conceive. The demographic assumption is that the reproductive
lifespan runs from 15-50, so 49.25 is set as the default value
(making 50 the latest age at which one has children).This is in exact
age and not age at last birthday,so 50 years and one day is not
within the reproductive lifespan.

{contraceptioneffectiveness} This is the effectiveness rate of
contraception. A contraceptive practice that works 70% of the time
would have a rate of .7. The default value here is 0, or no
contraception.

{probabilitymiscarriage} This is the probability that any given pregnancy
will end in miscarriage. The default value is set at .25, which is
the average in the absence of induced abortion according to Preston,
Heuvaline, and Guillot's (2001).

{fetallossinfertility} This is the number of months of infertility due to
a miscarriage, including months of reproductive lifespan used up by
the initial pregnancy. The default value is set to 4, (three months
pregnant, one month postpartum) which is average (Preston, Heuvaline,
and Guillot 2001).

{birthinfertility} This is the number of months of infertility due to a
live birth. The default is set at 12 (9 months pregnancy, 3 months
postpartum), which assumes an absence of breastfeeding.

{endyear} This is the year that the simulation ends, it could be
considered the death date, but any date after the last date of
reproduction will suffice.

{birthday} This is the numerical day of the month that the woman was
born.

{birthmonth} This is the numerical month that the woman was born (1=Jan,
etc.)

{birthyear} This is the numerical year that the woman was born, it also
represents the beginning year of the simulation.

{marriageday} This is the numerical day of the month that the woman began
having sex.

{marriagemonth} This is the numerical month that the woman started having
sex.

{marriageyear} This is the numerical year that the woman started having
sex.

Example

birthsim, marriageyear(2005) marriagemonth(5) marriageday(1)
birthyear(1985) birthmonth(5) birthday(5) endyear(2100)

simulate children=r(children), nodots reps(1000): birthsim

Author

Stephen Cranney, PhD Candidate in Sociology/Demography, University of
Pennsylvania
scranney@sas.upenn.edu

Reference

Preston, Samuel H., Patrick Heuveline, and Michel Guillot. "Demography:
measuring and modeling population processes," 2001.

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