I am currently working on a project involving a variable that represents the severity of a disease on an ordinal scale of 1 to 4, where 1 represents the least severe and 4 represents the most severe. Conceptually, this variable seems categorical in nature as it represents different ordered categories of disease severity.
The question I am grappling with revolves around the treatment of this variable. I initially planned to treat this variable as a factor (considering it categorical) to account for the distinct levels of severity, which are not necessarily evenly spaced nor do they represent a linear increase in severity.
However, my superiors have instructed me to treat this variable "as is", i.e., as a numeric variable, without converting it into a factor. This directive has left me questioning the statistical correctness and potential implications of such an approach.
My concerns are:
Is it statistically valid to treat an ordinal variable as numeric? Could this potentially lead to misleading results, given that the distance between each successive category might not represent a consistent increase in disease severity? Or is it a common practice in certain statistical analyses to treat ordinal variables as numeric? Any guidance or advice on this matter would be greatly appreciated. Particularly, I would be grateful for any references or resources that could shed light on this topic to better inform my approach and discussion with my team.