page will calculate the z-ratio for the significance of the difference between two independent proportions, pa
. For the notation used here, na
represent the total numbers of observations in two independent samples, A and B; ka and
represent the numbers of observations within each sample that are of particular interest; and pa
represent the proportions
ka/na and kb/nb,
respectively. Thus, if sample A shows 23 recoveries among 60 patients, na=60, ka=23,
and the proportion is pa=23/60=0.3833. If sample B
shows 18 recoveries among 72 patients, nb=72, kb=18,
and the proportion is pb=18/72=0.2500.
The difference between the two proportions is diff=papb=0.38330.2500=0.1333.
To perform the calculation, enter the values of n and k
for samples A and B in the designated places, then click the «Calculate» button. Please note that this procedure can be validly employed only if both samples satisfy the standard binomial requirement: that n(p)
must both be equal to or greater than 5.
The one-tailed and two-tailed probabilities associated with the resulting value of z will be calculated and displayed in the designated text cells.
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©Richard Lowry 2001-
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