Carl Bialik of the Wall Street Journal takes a look at the grimy rot that is government economic statistics.  It has probably occurred to you at some point that there is uncertainty about whether numbers like the Gross Domestic Product (GDP) actually measure economic activity or are a reasonable proxy for well being.  What has not perhaps occurred to you is that maybe we aren’t all that certain about whether those numbers are accurate at all?

[A]t a time when high unemployment tops many people’s worries about the economic recovery, the BLS can say only that it is 90% confident that the true change in the number of unemployed in March was somewhere between a drop of 243,000 and an increase of 511,000. In other words, it isn’t even clear whether the number of unemployed rose or fell last month.

That emphasis is mine, and it is a point worth emphasizing.

Another important point, of course, is that it’s not my fault!   Aside from the point that the numbers might not represent what we think they represent, it is also important to note that we are trying to measure things that are difficult to measure with questionable samples in a short time horizon.  So always be sure to ask for the confidence interval.