Line charts with trend lines can be misleading. They can provide a kind of “false positive” that implies improvement where there is none. Here’s why:
“Hi, I’m Jay Arthur, author of “Agile Process Innovation.”
“I go to all these trade shows and I see a lot of poster presentations but they’re using line charts and then they draw a trend line through them and then they say, “Oh, we made an improvement.” No you didn’t. If it doesn’t really fit the line very well, if your goodness-of-fit metric is less than 80%, I’m not buying it. But nobody gives me a goodness-of-fit metric called r-squared, they just show me a line graph or a bar chart and then they show a little line through it.