Table 6. Alternative patterns for future fertility trerds

||Defi<br>|nin<br>Ste<br>|g<br>charac<br>rility<br>|teristics<br> <br>Transitio<br>|n<br> <br> <br>|
|---|---|---|---|---|---|
|Pattern|NR|(p|ercent|E(0) started|Projected<br>fertitity<br>trend|
|1 Pre-transition,<br>high sterility<br>|*2<br>||26<br>|<50<br>No<br> <br>|TFRrises<br>with reduced<br>sterility<br>|
|2 Pre-transition,<br>Low sterility<br>3 ii<br>|>2<br>||'6<br>|'50<br>No<br> <br>|TFRconstant<br> <br> <br>|
|Transton<br>starting,<br>high sterility<br>4Titi i|>2<br>'||>6<br>|tS0<br>No<br> <br>|Transition<br>starts;<br>mediumTFRdecline<br>(reduced<br>by half in first<br>quinquenmium)<br>adjusted for reduced sterility<br>|
|ranson startng,<br>low sterility<br> <br>|>2<br> <br>||<6<br>|S0<br>No<br> <br>|Transition starts; medium TFR decLine<br>(reduced<br>by half in first<br>quinquennium)<br>|
|5 Transition<br>continuin<br>high sterility<br> <br>|g,<br>>2<br> <br>||6<br>|>50<br>Yes<br> <br>|TFR decline based on previous decline,<br>adjusted<br>for reduced<br>sterility<br> <br> <br>|
|6 Transition<br>continuin<br>low sterilits<br> <br>|g,<br>>2<br>||6<br>|50<br>Yes<br> <br>|TFRdecline<br>based on previous<br>decline<br> <br> <br> <br>|
|7 Transition<br>ending<br>|)1 a<br>52<br>|nd|any<br>value|>50<br>Yes<br> <br> <br>|TFRdecline<br>follows<br>geometric<br>path to<br>replacement<br> <br>|
|8Post-transition,<br>at replacement<br>9 Pttiti|=I<br>||any<br>value<br>|>50<br>Yes<br> <br>|TFRstays at replacement<br>(if drop is<br>recent, it may fall below for I period)<br>|
|os-ranson,<br>below reptacement|<1||any<br>value|>50<br>Yes|TFR constant for 3 periods, then recovers<br>to replacement by 2030 (recent drop may<br>continue for 1 period)|

quinquennium, and this relationship can therefore be used to project future fertility decline during the transition. We estimated a simple model of annual TFR change: 4,TFR = _-.05_ + _.5_ (A4TFR), where 4A.TFR is the average annual rate of change in TFR in the preceding quinquennium. On the assumption that exceptionally slow or rapid TFR decline is unlikely to be sustained for long, we require that projected declines should be no slower than half the medium annual rate of decline (using .12 points as the medium) and no faster than twice the medium annual rate of decline, giving a lower bound of .06 and an upper bound of .24.

No indicators were found for the pace of future transitional decline where transition has not started. We therefore apply to such countries the average decline in past data, of .12 TFR points annually. For the first quinquennium, however, we apply only half this rate, assuming that, on average, the decline should start in the middle of the period. Figure _5_ shows the medium trend applied in such cases, as well as the upper and lower bounds within which all declines must fall.

Late and post-transition. We noted that TFR decline usually slows down when countries **are** in the late stages of the transition, i.e., when TFR drops below 3. The level at which TFR stops falling cannot be predicted from the trend in fertility at higher levels; it has been anywhere from 1.3 to 2.4. For long-term projections, we must assume that each country reaches replacement fertility at some point, in order to avoid extinction, on one hand, and unending population growth, on the other. Fluctuations around replacement fertility would of course be an alternative, but no basis exists for projecting such fluctuations. We assume, then, that the fertility transition ends in replacement fertility, and that the last point of TFR decline takes 15 years along a geometric (decelerating) path. For countries with data, the last point of TFR decline actually took 14.4 years on average (implying an annual rate of geometric change of -.0254). An exception is made for countries experiencing very slow fertility 17