extendedStatistic 
  The extended statistic for the metric specified in MetricName. When you call PutMetricAlarm and specify a MetricName, you must specify either Statistic or ExtendedStatistic but not both.
If you specify ExtendedStatistic, the following are valid values:
- p90
- tm90
- tc90
- ts90
- wm90
- IQM
- PR(<i>n</i>:<i>m</i>)where n and m are values of the metric
- TC(<i>X</i>%:<i>X</i>%)where X is between 10 and 90 inclusive.
- TM(<i>X</i>%:<i>X</i>%)where X is between 10 and 90 inclusive.
- TS(<i>X</i>%:<i>X</i>%)where X is between 10 and 90 inclusive.
- WM(<i>X</i>%:<i>X</i>%)where X is between 10 and 90 inclusive.
For more information about these extended statistics, see CloudWatch statistics definitions.