The September jobs report, which revealed a surprising drop in the unemployment rate, immediately provoked conspiracy theories among the Obama administration’s critics.

Former General Electric chief Jack Welch on Friday kicked off the speculation with this morning post on his Twitter account: “these Chicago guys will do anything. can’t debate so change numbers,” implying that the Obama administration had artificially inflated the figures.

Welch’s statement was quickly dismissed, even provoking a statement by a former Bureau of Labor Statistics commissioner, and there is no evidence that the numbers were tainted. But the speculation raises a broader question: How does the Bureau of Labor Statistics derive these numbers? How accurate is that process? And how susceptible is it to tampering?

The jobs report is actually a compilation of two different surveys: the Current Population Survey, which is commonly dubbed the “household survey,” and the Current Economic Statistics, or the “employer survey.” The household survey produces the unemployment rate — 7.8 percent in September — and the employer survey produces the “nonfarm payrolls” number, which is the most common measure of jobs gained and reached (14,000 last month).

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