@laurenhosking wrote: Fabulous thank you so much for your help . Just to clarify my measurement level of this variable would be ratio not interval in this case?
Sorry for the confusion and for the delay (I was offline for a while -- thanks to @PaigeMiller and @PGStats for stepping in). In general, the highest measurement scale is relevant, in your case ratio. But this doesn't mean that the weaker criteria of the lower levels in the hierarchy of scales are violated. Statistical methods for those could be applied to a ratio variable, too, but they would tend to be less powerful (than methods for ratio variables) because not all information would be used.
As mentioned, the exam result also shares the characteristics of an interval scale variable and you could even go a step further "down:" classify the percentages into ranges, e.g., 80-100%, 70-<80%, etc., denote these ranges as A, B, etc. and thus create an ordinal variable, albeit losing information (such as the difference between 85% and 90% or the ratio of 84% vs. 72%). Edit (addendum): Similarly, the ranges could be chosen narrow enough so that each distinct value had its own interval. This amounts to assigning ranks to the original values and thus using the exam results as an ordinal variable.
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