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Confidence Intervals - Proportions. Objective. Construct a Proportion Confidence Interval and Find Sample Size. Relevance. Can Estimate Population Parameters from Sample Statistics. Remember……. If x = the number of successes and n = the number of trials then.
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Objective Construct a Proportion Confidence Interval and Find Sample Size.
Relevance Can Estimate Population Parameters from Sample Statistics
If x = the number of successes and n = the number of trials then
Finding the sample proportion if not given…… • In a survey of 250 households, 178 had radios.
Example…… • A sample of 200,000 was taken on most popular boat names. 6% are named “Osprey.” Find a 95% confidence interval of the true proportion of boats named “Osprey.”
Example…… • In a sample of 1001 U.S. adults, 58% think that airplanes are the safest mode of transportation. Construct a 99% confidence interval.
Example…… • A sample of 500 nurses included 60 men. Find the 90% confidence interval of the true proportion of men who applied to the nursing program.
Confidence Intervals - Proportions Finding Sample Size
Finding Sample Size of a Proportion…… • Formula:
Example…… • Estimate with 95% confidence the number of people who own a home computer. A previous study showed that 40% of those interviewed had a computer at home. The researcher wishes to be accurate within 2% of the true proportion. Find the minimum sample size necessary.
Values: Plug In: Answer……
You Try…… • A researcher wishes to estimate the proportion of executives who own a car phone. A previous study showed that 50% owned a car phone. She wants to be 90%confident and be accurate to within 5% of the true proportion. Find the minimum sample size necessary.
Values: Plug In: Answer……