First and most important is the trick of missingness. The best way to make data look better is to take out data that you do not like or not bother to collect it at all. If the presentation does not account for missing data, all sorts of mischief are possible.
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Second is the trick of not showing a planned analysis, or alternatively, showing an analysis that was not planned.
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To be clear, these are not the only two tricks that people can play with the data from a clinical trial. But they cover a lot of ground.