Why is this data from 2011–2015 instead of just 2015?

After 2000, the Census began collecting a lot of their data through an ongoing survey called the American Community Survey mailed to a small sample of households — instead of through their once–every–ten–year door–to–door survey. Now they pull together five years of American Community Surveys to have a large enough sample in any one neighborhood to provide estimates for that neighborhood. For this reason, data for 2011–2015 describe average conditions reported during the period of January 2011 – December 2015.

How do I write about the 2011–2015 data in a grant report?

Here are some examples of how you can write about this data in a grant report:

“Looking across the five years from 2011 to 2015, the Census Bureau estimates that X% of residents had a high school education or higher…”

“In the five years following 2011, neighborhood statistical area X has experienced a poverty rate of…”

“From 2011 to 2015, X% of residents reported having a commute of X minutes or more to work…”

Source: American Community Survey (ACS) Guide. Metropolitan Area Planning Council. Retrieved May 17, 2012 from http://www.mapc.org/sites/default/files/MAPC-Guide-to-American-Community%20Survey.pdf