On Sun, 2 Jun 2019, Fred Engst wrote: The argument passed to ols and related commands is a list (of series) and a list can only contain named series (members of the dataset, with ID numbers). So you can employ any function that returns a list, or that creates a named series. This includes log, lags, diff, ldiff, sdiff, square, dummify, cdummify, dropcoll You cannot, for example, do ols y 0 x^3 because "x^3" just gives an anonymous result, that must be assigned a name and ID number before it can feature in a list. This isn't documented as such; it probably should be. But for each of the relevant functions it's documented that they either return a list or create an automatically named series. Allin