Google内容实验不会选择变体

Question

我有以下脚本：

<script src="//www.google-analytics.com/cx/api.js?experiment=XXXXXXXXXXXXXXXXXXXXXXX"></script>
<script>

  // Determine the current chosen variation
  console.log( cxApi.getChosenVariation() ); // returns -1 (equivalent to cxApi.NO_CHOSEN_VARIATION)

  // Tell Google to choose a variation for me
  var variation = cxApi.chooseVariation();
  console.log( variation );  // returns 0  <-- original variation

  // Determine current chosen variation again
  console.log( cxApi.getChosenVariation() ); // returns -1 again... why?

  // Lets force a chosen variation:
  variation = cxApi.setChosenVariation(1);

  // And determine the chosen variation one more time:
  console.log( variation ); // returns 1, as expected

</script>

那么这里发生了什么？似乎使用chooseVariation()无效。谷歌没有为我选择变种。它返回零，但后来它说没有选择变化。只有当我自己选择变体时，一切似乎都有效。