This is exactly why I don't send out the slides, or post them online.Sure, some students are probably more likely to skip if powerpoints are provided, but I think that it would come back to hurt those students in the long run. I think the key is to make the students apply the topics that are being presented. Sure, if the tests are straight facts out of the slides than people are going to zone out or not even come, but if the tests force the students to apply the concepts taught then attendance and attention are necessary. I know that for many of my classes the tests could practically be open note and still be challenging because they require a level of critical thinking and problem solving that goes beyond the powerpoint slides. That said, I do think it matters what type of course it is for whether making powerpoints available is necessary or not. It all depends on the subject matter to me.