From time to time strangers email to ask a question on test construction, which I do my best to answer. If they are the sort of questions that I get a lot, I add them to the "Frequently Asked Questions" file on the test construction site; but I think I'll highlight some of them here in the blog as well.
Q: Where is the best place to put the correct answer? For example, if I provide seven choices, does it make a difference if the correct answer is choice 'b' instead of choice 'e'?
A: Professional test designers place the answers randomly -- I mean that in the literal statistical sense of the word, not 'wherever'. They use tables of random numbers, or complicated computer programs that assign the answer randomly, to decide which spot will hold the answer to each question.
What they do NOT do is place it themselves. Research shows that left to our own devices, most people will attempt to 'hide' the correct answer somewhere in the middle of the list. (Nobody wants to put the right answer in A, because then the students won't even read the other alternatives you worked so hard on; and putting it in 'e', it just sort of seems to hang out there over the edge. Sticking it in the middle feels right! Even though, that's wrong.) Even experienced test construction professionals will unconsciously choose 'c' (or for some individuals, it turns out to be 'b') 3/4 of the time. That's why the rule for taking an mc test is "when in doubt, choose 'c'" -- because unless one takes care to distribute correct answers to get an equal distribution of A, B, C,D, etc, there will be way more 'b's and especially 'c's than other answers, so testwise students can do quite well for themselves simply by answering 'C' to every question. That's why professionals force themselves to do it randomly by using computers or tables of random numbers. And then they'll double check at the end of the test to make sure they have roughly equal number of a, b, c, d, etc.
For classroom instructors etc, I wouldn't bother with tables of random numbers (which are kind of a pain to work with) and let the answers fall where they may by pyramiding questions. To stop students from trying to figure out which answer will come next ("there have been three 'd's in a row so next one must be something else") you let the internal logic of the question dictate placement. Numerical answers are listed in ascending or descending order; dates in chronological order, single word answers are listed in alphabetical order; sentences either on the basis of some internal logic or more usually shortest to longest or longest to shortest. (Incidentally, this also makes the test look really pretty! People who don't pyramid their tests have really ragged looking questions). So if the correct answer turns out to be the longest, it places itself in the 'e' slot, not letting the designer 'hide' it in the middle 'c' spot. After the initial draft of the test is done, one quickly looks through to ensure one has equal numbers of a, b, c,s etc. Where there are too many of one, say 'A's, you go through and change some of the ascending questions to a descending to move the 'A' to a "D" or whatever. It works pretty well!