Just over four years ago, D.C. became the first jurisdiction in the country to require businesses to charge consumers for each plastic bag. Since then, bag fees have been implemented across the country, from Los Angeles to Nantucket to Montgomery County in Maryland.

To check the bag fee's effectiveness, the District Department of the Environment (DDOE) contracted with independent research firm OpinionWorks to survey residents and business owners; the results of that survey (conducted in January 2013, three years after the bag law went into effect) have now been released.

In short, the study, which asked residents and business owners about their perceptions of the law and attempted to quantify bag usage based on self-reporting, shows a dramatic drop in the number of plastic bags given out by retailers, used by residents, and seen blowing around on D.C. streets. But tax revenue numbers paint a different picture, the Post reports. 

Part of the five cents collected by grocery stores and liquor stores per bag goes back to the District to fund river cleanup efforts (and studies like this one). Tax data from the city shows that bag fee collections have remained "remarkably stable."

It's important to note that when the bag fee went into effect in 2010, the District's population was at least 45,000 less. There were no Wal-Marts. Ten grocery stores opened between 2010 and the third quarter of 2013. With population, number of stores and incomes in D.C. rising, it may be less of a surprise that as residents and businesses reported less bag use, the total number of bags paid for remained steady.

Elevation DC put together an infographic summarizing the findings.