About one-third of Americans describe themselves as independent voters, creating a widespread impression that a large group of Americans will provide the decisive swing votes in this year’s election. But that impression is misleading, polling experts and political scientists say.

Many self-described independents — close to half, according to surveys — reliably vote for one party or the other. And many true swing voters live in states, like California or Texas, where no analyst doubts the outcome in November. …

The share of swing voters may even have declined in recent years, as many voters have become more reliably partisan. A report by the Pew Research Center found that self-identified Democrats are more liberal than in the past and self-identified Republicans are more conservative.