The Statistics menu gives these summary statistics for numeric columns:
N 
The sum of all weight values in a column. (See Column Properties in The Column Info Window.) Or, if no column is assigned the weight role, Sum Wgt is the total number of nonmissing values.
The standard error of the mean. It is the standard deviation divided by the square root of N. If a column is assigned the role of weight, then the denominator is the square root of the sum of the weights.