Embarking on a new TV show is always a calculated risk for us viewers — we never know if the time we’re investing will pay off or whether the show will receive an unceremoniously yanked from the schedule. But that gamble gets a little less risky and a little more calculated thanks to TV by the Numbers’ Renew/Cancel Index, which compares the ratings of scripted series against each network’s averages (and takes into consideration other trends) to predict each...