WASHINGTON — Six years ago this week, the Supreme Court transformed civil litigation in the federal courts, making it much easier for judges to dismiss cases soon after they are filed.

The decision, Ashcroft v. Iqbal, may be the most consequential ruling in Chief Justice John G. Roberts Jr.’s 10-year tenure.

It has been cited in more than 85,000 lower-court decisions. But lawyers and law professors continue to differ about its practical effects, which are harder to measure than one may think. The latest and probably most thorough in a long series of studies, to be published in the Virginia Law Review, concluded that the decision had hit the powerless the hardest.

Before Iqbal, cases brought by individuals represented by lawyers were dismissed 42 percent of the time. After Iqbal, the rate was 59 percent. For corporate plaintiffs, the rates of dismissal stayed basically flat, edging up to 38 percent from 37 percent.