A reader writing a report emailed me to ask:
Should I write “compared to previous years” or “compared with previous years” or doesn’t it matter?
Here is what three popular handbooks have to say on the matter.
Strunk and White (The Elements of Style)
To compare to is to point out or imply resemblances between objects regarded as essentially of a different order;
to compare with is mainly to point out differences between objects regarded as essentially of the same order.
Thus, life has been compared to a pilgrimage, to a drama, to a battle; Congress may be compared with the British Parliament. Paris has been compared to ancient Athens; it may be compared with modern London.
Use compared to when the intent is to assert, without the need for elaboration, that two or more items are similar: She compared her work for women’s rights to Susan B Anthony’s campaign for women’s suffrage.
Use compared with when juxtaposing two or more items to illustrate similarities and/or differences: His time was 2:11:10 compared with 2:14 for his closest competitor.
Penguin Writer’s Manual
Both prepositions, to and with, can be used following compare. Neither is more correct than the other, but a slight distinction can be made in meaning.
To has traditionally been preferred when the similarity between two things is the point of the comparison and compare means ‘liken’: I hesitate to compare my own works to those of someone like Dickens.
With, on the other hand, suggests that the differences between two things are as important as, if not more important than, the similarities: We compared the facilities available to most city-dwellers with those available to people living in the country; to compare like with like.
When compare is used intransitively it should be followed by with: Our output simply cannot compare with theirs.
Bottomline: If the differences are important, say compared with.