" Since the leagues split into three divisions, 53 of the 78 teams (67.9 percent) who led a division at the All-Star break finished the season there. Over the past 10 years, 50 of the 80 teams (62.5 percent) that were in first place in either a division or a Wild Card race at the break made the playoffs.
Being on top when the July break arrives is no guarantee of an October invitation, though. During the past decade, two or more leaders at the break were unable to make the playoffs each year, except in 2000, when seven of eight leaders held on for postseason berths.
Last year, all four National League leaders at the break -- the Mets, Brewers, Padres and the Wild Card-leading Dodgers -- did not make the playoffs."