Tennis line judges are more likely to make mistakes when calling balls "out" rather than "in", say researchers. This was [due] to a time lag of a few hundred milliseconds between an image hitting the retina and the viewer processing it, the team said. This bias, revealed in Current Biology, could enable players to exploit the "challenge" system, they suggested. To test this, video clips of 4,000 random Wimbledon points were examined and any incorrect calls logged. If this "bias" did not exist scientists would have expected the number of balls wrongly called "out" to equal the number wrongly judged "in". In fact, of 83 calls, 70 of the errors were wrong "out" calls.BBC News - From watching just the grand slam events, the majority of overturned line calls go from "out" to "in". Of course, this could be because players mostly challenge "out" calls. Ah, Type I and II errors, how you plague us.