Cooper, Heron & Heward (2007, p. 149) say if you do visual analysis, you must look at three things.
- Trends of data
- The level of data
- The extent in type of variability and data
"You need to look at variability or stability, you need to look at level, and you need to look at trend."
Do I have to convince anybody that if you are doing visual analysis, these things are important?
You probably agree with me. This is just how we do our business.
Take a look at the first graph below. We have an ascending trend, then we have another ascending trend. How many would be convinced that the intervention was good? That the progress happened as a result of the intervention itself? Would you be suspicious?
Now look at the second graph. If it's flat and then it goes up, that's convincing. And the third graph? If we have something that's going down and our intervention makes it go up, we can convince people of our effectiveness. This is part of trend analysis.
Let's just say we have the average in baseline, which is a 2. Then you do something, now the average is a 10. Do we have an effect? Yes! You went from 2 to 10.
You're doing this through visual analysis.
Imagine that you have data points that are bouncing around and those two lines below are showing you what's called the variability envelope.
So here's my question to you:
Where does visual analysis occur?
Laboratory settings. Maybe you do work in labs and do visual analysis there. Maybe you are doing applied work where, again, visual analysis is frequent. You did a thesis, you did a dissertation? You probably did visual analysis.
Now, here is a critical question:
What does visual analysis rely upon?
Think about this for one minute. All that stuff about trend, level, variability; if you have a compromised visual graphic, how good is your analysis? It will likely also be negatively affected. I can't tell you how important it is that we have a very good graph when we're making decisions. All of those things that I just shared with you; how we move our science forward, how we make applied decisions, how we affect lives. Everything is reliant upon a graph.
So would you believe no one has ever done a study, not once, ever, to see how well we actually make graphs? No one's ever done it. I don't know why. But I decided that's something I needed to do. More on that later...
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