3/27/2013

Choosing the sample size

• Example - You wish to use a random sample of size n to construct an approximate C.I. for p (pi) that will have margin of error no greater than 0.05. How large should n be if you want your approximate confidence in the interval to be 95%?

Confidence intervals for a population mean

• When the population standard deviation is known (VERY UNREALISTIC)
• When the population standard deviation is unknown (WIDELY USED)
• Example - Exercise 9.44 on p. 443

Relationship between normal and t-distributions

• There is a different t distribution for each sample size.
• The degrees of freedom for this statistic comes from the standard deviation s.
• t distributions are very similar to the N(0,1) distribution. The major difference is that t distributions have more area in the tails than the N(0, 1) distribution.
• As the sample size increases, t distributions get closer to the N(0, 1) distribution.

Hypothesis Testing Handout

Please read Sections 10.2 and 10.3 for class on Friday.