Table : TABLE 17-8. The Chi-Square Calculations For the chi-square test for independence calculations, we use the same format as we did for the chi-square test for goodness of fit. We calculate the difference between each observed frequency and expected frequency, square the difference, then divide each square by its appropriate expected frequency. Finally, we add up the numbers in the last column, which gives us the chi-square statistic.
CategoryObserved (O)Expected (E)OE(OE)2
Clown; pregnant3325.482  7.51856.5202.218
Clown; not pregnant6067.518−7.51856.5200.837
No clown; pregnant1825.482−7.48255.9802.197
No clown; not pregnant7567.5187.48255.9800.829