What is the difference between a nominal and ordinal categorical variable? What type of variable is ocular discomfort? 

Ophthalmology

Dry eye is the most prevalent form of ocular discomfort and irritation, with approximately 20 million people in the United States having mild to moderate dry eye. A small clinical trial was performed to compare the effectiveness of an active drug vs. placebo for relieving symptoms of dry eye. Specifically, patients were randomized to either active drug or placebo for 2 weeks. They then came for a clinic visit where they were exposed to a chamber with a controlled  adverse environment (CAE) for 90 minutes (with low humidity intended to exacerbate symptoms of dry eye). The patients were then asked to report their degree of discomfort while in the CAE using the following scale: (0 = none, 1 = intermittent awareness, 2 = constant awareness, 3 = intermittent discomfort, 4 = constant discomfort). The results by treatment group are shown in Table 10.45.

Table 10.45: Comparison of active drug vs. placebo for the prevention of dry eye symptoms

 

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Ocular discomfort 4 3 Total Active drug 37 17 60 59 44 Placebo 13