With the exception of the hilly states of the north-east, Chhattisgarh has one of highest shares of Scheduled Tribe (ST) populations within a state, accounting for about 10 percent of the STs in India. Scheduled Castes and STs together constitute more than 50 percent of the states population. The tribals are an important part of the state population and mainly inhabit the dense forests of Bastar and other districts of south Chhattisgarh. The Scheduled Caste (SC) population of Chhattisgarh is 2,418,722 as per 2001 census constituting 11.6 percent of the total population (20,833,803). The proportion of Scheduled Castes has increased from 11.6 percent in 2001 to 12.8% in 2011. The percentage increase in the population of the scheduled list of tribals during the 2001–2011 decade had been at the rate of 18.23 percent. The share of the tribal population in the entire state had been 30.62 per cent which was 31.76 per cent during 2001.. How many years does this census account for?