Only 25% turnout in US presidential primaries

With Bernie Sanders endorsing Hillary Clinton, the curtains have come down on one of the most rollicking primary seasons in the US. Now, both the dominant parties, Democrats and Republicans head for their respective national conventions this month to formally announce their candidates for presidential elections.
But an analysis of voter turnout data shows an astonishing indifference in people to what was a high profile and bitterly fought election on which over $1.3 billion was spent by candidates.Just 25% of the total voting eligible population cast their votes in the primaries of the two parties.This was nearly equally divided between them.
Michael MacDonald of the University of Florida has been collating voter turnout data for the past several years in his US Election Project. Collation is often delayed because counting procedures and time allowed vary with states.
Although the voting age population is estimated at about 265 million, the number of eligible voters who are registered with state election commissions is only 240 million. Those omitted mainly include people who have not registered or whose names have got dropped because of bureaucratic issues. Also omitted are about 1.56 million prisoners and 4.7 million probationers and parolees under various state laws. So, out of a total 240 million istered voters, about 61 million voted in the primaries.
No definitive figures are available about the number of people who have registered as either Democrats or Republicans. These lists are held by State Party Committees. In the current election, Democratic Party units in several states allowed registered Independents and even freshly registered voters to vote.
An idea of how many associate themselves with either Democrats or Republicans can be gleaned from a Pew Research Center survey of party affiliations done in 2014. It revealed that 23% of the adult population supported Republicans and 32% backed Democrats. Over 45% declared themselves either as independent or having no preference. Such surveys have been done since 1939 and the share of independents or no preferences was highest in 2014 indicating a growing disillusionment from mainstream parties.