This presents an interesting dilemma, but the answer is the same either way.
Is the dash showing the omission of a word, or is it showing the omission of sign of comparison?
If the omission is replaced with words, ("is less than" "is greater than" "equals") there is no doubt that the variable requires an ELI. If, on the other hand, the dash is replacing a comparison sign, can the ELI be omitted?
Although NC Section 57 tells us we must use a "long dash" to represent an omission printed as a dash, there is no rule in the Nemeth Code stating that the dash is to follow the rules of the sign which it replaces.
We must look at the variable in your example as a single letter preceded and followed by a space. An English letter indicator is required (NC Sec.25a and 26b), regardless of what the dash represents.
edited by Lindy on 11/19/2011