Subscriptions! Specifically, the ones that Apple can measure via the Podcasts and iTunes apps. iTunes' Top 200 lists are based on number of New Subscribers in the last week, with a weighted average for the last 24, 48 and 72 hours. Downloads, ratings and reviews have ZERO effect on your Top 200 ranking. Note that this is all by country, so a show in the Top 200 in one country may be nowhere to be seen in another. Downloads only count towards the Top Episodes list, and a little for the What's Hot list.