Frequency of appropriate and inappropriate presentation and analysis methods of ordered categorical data in the veterinary dermatology literature from January 2003 to June 2006

Abstract

What is known about the topic of this paper • Ordered categorical level data do not contain as much information as interval level data.• Ordered categorical scales require statistical methodology different than that required for continuous data in order to be consistent with the structure of the data.• Ordinal data are frequently presented and analysed with inappropriate methods in the human medical literature.

Effect of Parenteral Selenium Administration to Sheep on Prevalence and Recovery from Footrot

“…Analysis of the foot score data provided some challenges. Given that the data were categorical, nonparametric methods were considered most appropriate 22 . The Friedman nonparametric test is often cited as the most appropriate test for repeated measures; however, our experimental design was not workable with this test.…”

Clinical studies utilising ordinal data: Pitfalls in the analysis and interpretation of clinical grading systems

“…Nominal data comprise unordered categories such as gender, breed, colour and diagnosis. Because of the descriptive nature of these categories, the data cannot be ranked (Stevens 1946; Plant et al . 2007).…”

“…2007). For example, a Thoroughbred horse is different from a Shetland pony, but one of these values cannot be ranked ‘higher’ or ‘more’ than the other (Plant et al . 2007).…”

“…2001) and Havemeyer grading systems for laryngeal function. The limitation with these data is that the interval or distance between each grade is arbitrary in terms of its clinical meaning (Plant et al . 2007).…”

“…The degree of severity of clinical outcomes is typically measured on an ordinal scale using rankings or grades that can be described in words (mild, moderate or severe), using letters (A–D) or numbers (1–5). These grades are often findings for which precise measurements on a continuous scale are not available (Plant et al . 2007).…”