<< Click to Display Table of Contents >> Navigation:  Reference > Functions > %SIGI

This function is used to give the confidence interval for a proportion.

Form of use:

DW wvar = %SIGI (pl, n, x),

where the three arguments can be any arithmetic expression including table cells.

For example, if 18 (30%) out of 60 respondents give an answer we could use:

dw $inter = %sigi(95, 60, 18),

to set $INTER to the 95% confidence interval. Multiply this value by 100 to get the maximum expected percentage difference between the perceived figure (30%) and the real figure. The above example sets $INTER to 0.116 which means that there is a one in twenty chance that the real proportion is not within 11.6% of the perceived 30%.

Where z is the appropriate figure for the percentage level. See format SIG for table of figures.