"Making projections is not an exact science," declared a November 1993 paper released by the Bureau of Labor Statistics that made a series of projections. The "science" in that paper proved to be inexact, with key projections turning out to be very wide of the mark. The BLS released a similar paper just last month. The question is not whether its projections will also miss the mark, but by how much.

These periodic papers (such efforts by the BLS go back at least to 1965) focus on the science and art of predicting the future size of the labor force: the number of folks in the civilian, noninstitutional population over 16 who will choose to work at a paying job, or who are without a job but choose to look actively for work and are therefore counted as unemployed.

Since there are two main tricks to getting things right in this forecasting game, it's not surprising how often the forecasts prove wrong. The first is to predict the civilian population itself; even within periods of a decade or two, when virtually all those who will reach age 16 are already born, the number of working-age immigrants must also be reckoned with. Both questions of births and immigration come up in the bureau's recent paper, which projects the labor force to 2050.

The second trick is probably more difficult. Even if we know how many men and women of working age will be in the population, and what their age distribution will be, we must also forecast what percentage of each age group, for each gender, will choose to participate in the labor force.

The estimates of the labor-force participation rate of women has been the major blot on the BLS forecasting record. Its 1965 and 1970 efforts, targeting 1980, "grossly underprojected the female labor force," according to the agency's own appraisal. That was mainly because it grossly underappreciated women's zeal to get paying work. For example, its 1970 guess put the number of women in the labor force by 1980 at 37 million, against an actual figure of 45 million.

What should have made that eight million miss all the more embarrassing, but went unmentioned by the BLS, is that most of 1980 was a year of recession, with a soaring rate of joblessness among women -- a factor that normally puts a brake on labor-force participation. By the time the agency made its projections in November 1993, it made the opposite error. No doubt chastened by the seemingly unstoppable uptrend, the bureau assumed it would continue, this time targeting 2005. Women had a different idea.

The November 1993 paper tried a cautious "high," "moderate," and "low" projection for the labor-force size and participation by 2005 -- and even the low estimate for women proved too high. By 1997, the revolution in women's participation had ground to a halt. Since this occurred in the midst of a jobs boom, with rates of joblessness hitting record lows, you could not attribute it to transitory cyclical factors. From a high of 60% by 1999, the female participation rate has trended down since then, to 57.8% this October. But it has still come a long way from its 32.7% level in 1948, the first year the BLS began keeping records.

THE PARTICIPATION RATE OF MEN is still higher than that of women, at 70.3% in October. But it has been falling long-term, causing pretty consistent overprojections by the bureau. Even the "low" estimate in its November 1993 projection for male participation in 2005 proved too high. Especially disconcerting is the long-term decline in the participation rate of prime-aged men, 25 to 54, from an average of 97% through the 1950s and early-'60s, to 88.7% in October. But there's no compelling reason to assume the trend is incapable of reversing.

Another wild card is the steady rise since the mid-'90s in the participation rate of both men and women over 55. After falling for decades, no doubt because increasing affluence brought early retirement, both rates started to rise through the late-'90s. Since the turnarounds occurred during the bull market of the late-'90s, they were probably not due to anxiety over being able to afford retirement—although more recently that must be part of the reason. In any case, both trends have plenty of room to rise further.

Then there are the young people, 16 to 24, whose work habits are especially difficult to anticipate, depending on how much time they spend in school, and whether they seek part-time work while attending to their education. The trend in participation for both has been erratic over time. At 57.4% and 53.2% in October for young men and women, respectively, the trends could move in either direction from here.

Despite these wild cards, the BLS now projects through 2050 a continued decline in male and female participation. Well, maybe, but maybe not. And right now, the short-term trend in participation is anyone's guess.

The recent decline in overall participation could be due almost entirely to the cyclical tendency for participation to falter owing to high unemployment. As the unemployment rate continues to fall, the participation rate could turn back up. But that partly depends on the underlying long-term trends, which have yet to reveal themselves. When it comes to the future trend in the labor force, a wait-and-see attitude seems the wiser course. 

Comments? E-mail: gepstein@barrons.com