Table of Contents

• Testing differences
• 1: How to convince your boss
• 2: Looking at the data
• 3: Is the average different?
• 4: How big is big?
• 5: How to combine SDs
• 6: Combining SDs for fun and profit
• t-calc and t-crit
• 7: Getting to t-calc
• 8: A formula for t-calc
• 9: Degrees of freedom
• 10: The bottom line (finally)
• Putting it all together
• 11: Give it a try
• 12: Once more for luck
• 13: The big picture

The big picture

So now that you know all the arcane details of performing a t-test, let's take one last step back and look at the big picture. Remember that the number you are calculating is supposed to tell you how important your treatment was compared to the "random slop" in your experiment. As you move the sliders below, you can see how the mean and standard deviation in each group affects the t-test outcome.

Before you start pushing sliders, think about which part of the fraction should change as you move the averages farther apart or closer together? How will that affect the bottom line (whether or not your results are significant)?

And what will happen if you increase the SD for one or both treatments?

And how much overlap is too much?

 

 

 

If you want a printer-friendly version of this module, you can find it here in a Microsoft Word document. This printer-friendly version should be used only to review, as it does not contain any of the interactive material, and only a skeletal version of problems solved in the module.