Using Significance Tests Section 10.3

Practice safe statistics Be good statisticians Practice safe statistics Collect good data (no cure for bad data) Don’t treat statistical tests as sacred Use inference tests responsibly Look at the whole picture Look at the graph of your data (Most Important information) Are there outliers? Extreme skewness? How large of a sample did you use

Beware of really large samples because the sampling distribution becomes very narrow and even the slightest difference from mean may cause rejection of null. Use a confidence interval to help determine how much of an effect there really is, because a confidence interval actually emphasizes the size of an effect, rather than simply asking if the effect is too large to reasonably occur by chance alone.

Beware of doing many tests at one time, just by chance alone you are bound to find an incorrect conclusion.

How do you pick an an appropriate α level How do you pick an an appropriate α level? Ask yourself … “What are the consequences if I reject H0?” “If I fail to reject H0?” If I reject H0 does it put someone’s health at risk? The more certain you want to be that something is significantly different than something else – the lower the α level.

What do you if you get a p-value of 0. 0499 or 0 What do you if you get a p-value of 0.0499 or 0.0514 at an α level of 0.05? Let’s do #62 p.566 Assignment: Read pages 524 and 525 Some Cautions Pages 563-567 Problems 61-65 skip 62