Inference about Means/AveragesChapter 23

Looking at means rather than percentages

What did we use?:SE( ) for the sample meanA new model for small samples – “the student t model”Making a confidence interval for the meanTest a hypotheses about the population mean using the

sample mean

So what is the SE(mean) ?

n

sySE )(

Because we use the sample standard deviation rather than the population standard deviation there is inherent problem – to correct this we use a different model instead of the normal model. The new model is called “the student t” and is a family of models based on the sample size. The sample size determines which model you use. Degrees of Freedom or df are what we use to determine the model.Degrees of Freedom (df) = n - 1

Like all other confidence intervals and tests, there are:

Assumptions & Conditions

The confidence interval is:

)()*( ySEty df

The hypothesis test:same assumptions and conditions -

)(0

ySE

ytscore

)( scoretPp