AP statistics chapter 22 by Stats modelling the world third edition by David E. Bock

● Variances of independent - The variance of a sum or difference of independent
random variables is the sum of the variances random variables add of those
variables.
● Sampling distribution - The sampling distribution of is, under appropriate
assumptions, modeled by a Normal the difference between two proportions
model with mean and standard deviation .

● Two-proportion z-interval - A two-proportion z-interval gives a confidence interval
for the true difference in proportions, , in two independent groups. The
confidence interval is , where z\* is a critical value from the standard Normal
model corresponding to the specified confidence level.
● Pooling - When we have data from different sources that we believe are
homogeneous, we can get a better estimate of the common proportion and its
standard deviation. We can combine, or pool, the data into a single group for the
purpose of estimating the common proportion. The resulting pooled standard
error is based on more data and is thus more reliable (if the null hypothesis is
true and the groups are truly homogeneous). Two-proportion z-test - Test the null
hypothesis by referring the statistic to a standard Normal model.