Table of Contents

• Prequiz...
• 1: The Case of the Confusing Axes
• 2: Choose your x and y carefully
• 3: Practice labelling the axes
• 4: Next step: ranging the axes
• 5: Practice ranging the axes
• 6: Next step: scale the axes
• 7: Practice determining labelled tick distance
• 8: How to scale axes
• 9: Finally, fill in the axes
• 10: Final Words of Wisdom & Some Graph Paper

Choose your x and y carefully.

Scientists like to say that the "independent" variable goes on the x-axis (the bottom, horizontal one) and the "dependent" variable goes on the y-axis (the left side, vertical one). This does not mean that the x variable is out partying while the y variable is whining about the x variable never being around -- that's co-dependence, which is a completely different kettle of fish.

When you're talking about variables, "independent" means that the researcher (you, or someone else in a white coat) can pick any value they want for that variable. Using the TV viewing distance data, you can imagine the researcher putting little pieces of tape on the floor and positioning her small experimental subjects at just the right distance ... whereas I can't think of any way the researcher can directly control how much eyesight the kids lost.

Personally, I still mix up right and left, and I find the words "dependent" and "independent" a little confusing. So I think "cause" (the x variable) and "effect" (the y variable). This is not exactly right and will make some scientists apoplectic, but as a sort of memory aid, it might help you too. So,

•  The cause is how far the kid sits from the TV - the x variable

•  The effect is how much eyesight she loses - the y variable.

OK, now you try: for each pair, what is "x" and which is "y"?

OK, those two were easy. In both cases, the x variables (temperature of tank or amount of food given) are easily controlled by the experimenter. Sometimes the "x" variable can't actually be controlled but only "chosen" by researcher -- this is especially the case when some version of "time" is the x variable.

However, be careful. Just because a variable includes time does not mean that it is automatically the x variable. Sometimes the amount of time a process takes is the EFFECT of a treatment, and then its the "y" variable.

Did you get the Dilaudin example? In this case, the researcher is trying to find out how long it takes to get pain relief DEPENDING ON how much medication is given. The researcher can directly control (or choose) dosage, but not time.

Finally, data tables often contain many columns, so it's important to figure out which ones belong on a graph. Below, type "n" for data that will NOT be represented by either "x" or "y".