DATA AND **METHODS** b to 6 peremnt over three quinquennia, with each percentage point drop in sterility raising total fertility by .11 points (Frank 1983).

In the transition stage, the rate of fertility decline is based on the rate in the preceding quinquennium, assuming transition had already started in that period. With previous annual change represented by DTR, annual change during the transition is set at (-.05 + _.5_ DrpR). However, limits are set on this change: it must be at least -.073 points and at most -.210 points, which may be taken to define slow and rapid fertility decline. (Previous analysis in Bulatao and Elwan 1985 defined rapid decline as an annual total fertility change of -.2164 points, which is consistent.) If the formula does not apply because transition has just started, an average annual decline in total fertility of .06 points for the first five year of the transition and 0.12 annually for subsequent quinquennia is imposed. In the early part of the transition stage, the sterility adjustment is applied if appropriate to raise total fertilty slightly.

In the late-transition and posttransition stage, fertility approaches replacement level, either from slightly above or slightly below it. Four alternative patterns:

* Generally, a geometric function is imposed on total fertility decline from one point above replacement level to replacement level, with this decline assumed to take 15 years.

> i Where total fertility has shown unusually slow decline, it is assumed to take 20 rather than 15 years for total fertility to fall one point to replacement.

> * Where, toward the end of a fertility transition, total fertility is still recording rapid decUnes even though it is close to or even below replacement level (2.25 to 1.75), it is assumed to fall further for one period, generally going below replacement, to stay constant in the next period, and then to return to replacement.

* Where the transition has been completed and total fertility is below replacement, it is assumed to stay at the current level for two quinquennia, and then to return gradually to replacement, along a lnear path, by 2030.

In applying late-transition procedures, the level of total fertility that provides replacement is approximated by a quadratic formula based on female life expectancy (e(fl) in the replacement year: TFRNRR.I = 6.702 - .1107 e(g) + .0006592 e(u.

The replacement year is first approximated in order to determine life expectancy and then calculated given this formula and whichever pattern of fertility change above is appropriate.

For all stages of fertility transition, the age pattern of fertility is deLermined in the same fashion, depending on the level of total fertility (Figure A2). Two basic schedules of age-specific fertility are defined: for total fertility levels greater than six and for total fertility levels of three and lower. In between, age patterns are obtained by interpolation between the two schedules. At a total fertility level of six, a greater proportion of-births are at younger and older ages of the reproductive span, and the mean age of childbearing is 2&9 years. At a total fertility level of three, births are concentrated in a narrower band of ages, and the mean age of childbearing is 28.0.

These procedures were developed from preliminary analysis of total fertility trends in cross-national data (See Bos and Bulatao 1989). In the pretransition stage, countries showed mostly stable fertility. The transition stage was more interesting. Across 42 countries which started a fertility transition between 1955 and 1983, the average annual decline in total fertility ranged from 0.06 to 0.25