1. Large Sample
Confidence Interval
for a Proportion

2. 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 SE
4. Specify CI: sample statistic + ME
written as: (Sample Stat – ME, Sample Stat + ME)

3. 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