These are features typically found in chordates, although it is difficult to make more precise comparisons.

Well, that is fairly easy because we have a precise comparison.

I agree that precise comparisons between the American and Soviet programs are difficult, if not impossible.

Many tests develop a system of numerical scoring which makes it possible to make precise comparisons between the scores obtained by different individuals.

It is difficult to make a precise comparison with the general population, because estimates about the extent of the problem there also vary widely.

He made the first precise comparison of the mercury- and air-temperature scales.

Because they commissioned a special tabulation, precise comparisons with other areas are difficult.

With cross-sectional data it is not possible to make precise comparisons between changes in employment and economic activity over time.

A. It's hard to make a precise comparison.

The readings themselves are unreliable, so a precise comparison is impossible.