If the term "participation rate" were to be expanded to include the number of workers divided by the TOTAL NUMBER OF "peeps," then a sudden, large number of babies being born in a particular year (something having no bearing on the availability of jobs, or of labor) would have an enormous impact upon this "rate" - thus making the "rate" useless for economists / labor experts, etc.
The real answer is that the writer of the article used sloppy language and/or logic.
Regards,
Must be a LSM Gerbilist ('tards all).