Federal health officials sometimes pay for direct comparisons of drugs.

But in the book there is no direct comparison to the responses of the two groups.

In helping to answer this question two direct comparisons are available.

Very few people are making the direct comparison, but we think it is valid.

And these are in no way direct comparisons - that's near impossible.

But because the studies are being run in different ways, direct comparison of findings is impossible.

It is hard to make a direct comparison, for relative prices have changed.

Boundary changes however make a direct comparison with 1951 impossible.

But this year voting is spread out over two days, making a direct comparison difficult.

Both look amazing, but I can't find any direct comparison between the two parks.