Rates of employment and the percentage of increase employment are far from an exact science. Most of the surveying done is tallied from the Current Employment Survey, who looks only at businesses who participate in their survey. Once these numbers are complied the Bureau of Labor Statistics calculates these rates, and factors in variables to account for those who did not participate.
The problem with this approach is that the results can be skewed by things such as error rates and seasonal adjustment. This means that two surveys taken can yield different results. For one, margins of can be chosen conservatively or liberally, however, false information or manipulation of data can also achieve the same results.