Large Sample Confidence Interval

for a Proportion

CI for a sample proportion (p)Estimation Requirements

Constructing a CI for a sample proportion are valid when these conditions are met:

1. sampling method is simple random sampling (SRS)2. sample includes at least 10 successes and 10 failures( np > 10 AND nq > 10) where q=1-p

How to find CI for a proportion: (method same as described before)

1. sample statistic (use sample proportion to estimate population proportion)

2. CL (90%, 95%, 99%)3. ME= CV x SD or ME= CV x SE4. Specify CI: sample statistic + ME written as: (Sample Stat – ME, Sample Stat + ME)

Variability of Sample Proportion

• Must compute standard error(SE) of sampling distribution in order to construct a CI for the sample proportion

• When the population size is at least 10 times larger than the sample size, SE can be approximated by:

** this is found on table under single sample - proportion