For the period 2011-15, the estimated median annual income for a household in the town was $48,059, and the median income for a family was $96,005. Male full-time workers had a median income of $64,750 versus $39,278 for females. The per capita income for the town was $18,905. About 8.7% of families and 34.7% of the population were below the poverty line, including 18.2% of those under age 18 and 4.5% of those age 65 or over.
Question: How many years does the "period" last?
Answer: 5