Aim: How do we differentiate between different confidence intervals and sample sizes? Quiz Tomorrow

N ≥ 30 Use the z distribution

Example A survey of 30 adults found that the mean age of a persons’ primary vehicle is 5.6 years. Assuming the standard deviation of the population is 0.8 years, find the best point estimate of the population mean and the 99% confidence interval of the population mean.

N < 30 Use the t distribution Use the t table (Table F) to find the t distribution values  find where the d.f. and confidence columns meet

Example The data represent a sample of the number of home fires started by candles for the past several years. (Data are from the National Fire Protection Association.) Find the 99% confidence interval for the mean number of home fires started by candles each year

Sample Size

Example The college president asks the statistic teacher to estimate the average age of the students at their college. How large a sample is necessary? The statistic teacher would like to be 99% confident that he estimate should be accurate within 1 year. From a previous study, the standard deviation of the ages is known to be 3 years.

Proportions

Confidence Interval for Proportions

Example A sample of 500 nursing applications included 60 from men. Find the 90% confidence interval of the true proportion of men who applied to the nursing program. – Solution:

Sample Size for Proportions

Class Work Work on worksheet Use as a study guide for tomorrows quiz