Measuring the Immeasurable?

In statistics, we draw conclusions from data. But to get data, we need to be able to measure the variable(s) that we are interested in. Measuring can be very crude (say, a trait is absent or present) or rather sophisticated (the expression levels of large numbers of genes). In the social sciences or in medicine, in order to reach uniformity in measuring a particular condition and make results more comparable, a standard scale is often developed that everyone is using. But can we measure everything? Here is an unusual example of trying to measure the immeasurable:

Irritable bowel syndrome (IBS) is a disorder that leads to abdominal pain and cramping, changes in bowel movements, and other symptoms (PubMed). When trying to develop a drug for combating IBS, one way to measure its success is to look at stool consistency. You think that is immeasurable? In fact, there is a scale for measuring just that, called the Bristol stool scale, which classifies stool into seven categories. The following (graphic) picture explains the scale:

So, it seems, everything is measurable!