For election fanatics obsessively watching the race on Tuesday, a new Silicon Valley-backed start-up called VoteCastr offered a tantalizing promise: real-time voter turnout data that could predict, throughout the day, how many votes the candidates got in seven closely contested states.

In an unprecedented experiment, VoteCastr teamed up with Slate and Vice News to publish projections hours before the polls closed, breaking with a longstanding journalistic tradition of waiting until final votes are cast in each state before reporting the results.

Their methodology involves using a team of observers in dozens of precincts in the seven swing states to assess turnout for likely voters for Donald J. Trump and Hillary Clinton, whom they have identified using surveys. The states being watched by VoteCastr were Florida, Iowa, New Hampshire, Nevada, Ohio, Pennsylvania and Wisconsin.

Some political analysts were skeptical of VoteCastr’s efforts from the start, and warned that it could depress voter turnout in close states. (Writing in The Hill, the analyst Mark Plotkin called it irresponsible and “downright scary and disruptive.”)