title: Confusing cb results with ips cb_type
body: <p>Is cb_type ips expected to be much better than dm or dr?</p>
  <p>I wrote the script here (results included) <a href="https://gist.github.com/travisbrady/546b40a0ed328d8f83dbc6230ee83fec" rel="nofollow noreferrer">https://gist.github.com/travisbrady/546b40a0ed328d8f83dbc6230ee83fec</a> using the personalization bandit data from Tony Jebara's ML for personalization class and the evaluation metric (&quot;take rate&quot;) varies by a lot as I change the cb_type.
  Specifically 0.23 for dm, 0.79 for dr and 0.85 for ips. Those jumps are quite large so I'm wondering if I've misunderstood something.</p>
  <p>Is this expected? Is ips typically the better choice? In what circumstances is each cb_type preferred?</p>