For the first time in over a year, median annual income fell by a statistically significant amount from the previous month, according to a report from Sentier Research.

Median annual household income in February 2013 was $51,404, about 1.1 percent (or $590) lower than the January 2013 level of $51,994. The numbers are all pretax, and are adjusted for both inflation and seasonal changes.

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The analysts at Sentier Research (a company that provides demographic and income analysis, run by former Census Bureau officials) note that median income has been depressed recently by inflation. While inflation is still quite low, income growth has been so weak that even very little inflation is enough to wipe out whatever gains households are seeing in their paychecks.

The longer-run trends are even more depressing.

February’s median annual household income was 5.6 percent lower than it was in June 2009, the month the recovery technically began; 7.3 percent lower than in December 2007, when the most recent recession officially started; and 8.4 percent lower than in January 2000, the earliest date that this statistical series became available.

Why are incomes stagnating, even falling? David Leonhardt presented some possible theories last fall.