I'm setting a text with old style figures. As usual, number 1 in this font resembles the roman numeral 1 very strongly. That's fine, since they mean the same. But I notice that when the text uses the roman numeral 2, it's virtually impossible to know whether it's the roman numeral or the old style figure 11.
I know that you can tell which is which, but that's because you know that old style figures without ascenders have x-height while the height of small caps tend to be larger than x-height. Most readers don't know this, and that difference is hard to spot when reading a text even if you _do_ know it.
So I'm wondering if it's simply a bad typographic choice to use roman numerals and old style figures in the same text, and if I should replace the roman numerals with arabic numerals instead.
In case you wonder, the roman numerals are not used haphazardly here and there. In this text they're only used as names for two groups called "Group I" and "Group II".