I'm visualizing results from lab tests. Most of these results are numerical and therefore easily communicated using line graphs, where the x-axis is time and the y-axis is determined by the range of possible values, like
EDIT: To be clear, I'm not measuring frequency. I'm displaying an individual's lab test results for one specific test (like cholesterol) over time. Since most people don't get more than 1 or 2 lab tests a year, most people's graphs will have less than a dozen (x,y) values.
I'm less sure how to visualize this information when the y-axis values are categorical:
Sometimes the possible values are themselves ranges. A test value will be something like
2-6, meaning that the value falls between 2 and 6 — and that's all we need to know. Would it make sense to graph these values with something like error bars? Or would it make more sense to graph the average of the range (in this case, 4) as a regular line chart?
The other types involve categories which are non-numerical. Sometimes these are ordinal. In the ordinal case the categories might be something like
[none, few, moderate, many]. Does it make sense to just assign an index to each
[0, 1, 2, 3]and use a standard line graph? If not, what would make more sense?
Lastly, non-numerical, nominal types. These are categories with no clear rank hierarchy, like colors:
[yellow, orange, red]. In this case, I think it might be misleading to use a standard line graph, because it would imply that certain colors are "higher" or "better" than others. What would be appropriate?