@Substitution(name='<STR_LIT>')<EOL><INDENT>@Appender(_common_see_also)<EOL>def sem(self, ddof=<NUM_LIT:1>):<DEDENT>
return self.std(ddof=ddof) / np.sqrt(self.count())<EOL>
Compute standard error of the mean of groups, excluding missing values.

For multiple groupings, the result index will be a MultiIndex.

Parameters
----------
ddof : integer, default 1
    degrees of freedom