Your chances of winning a competition, whether a writing contest, or otherwise, are greatly influneced by the talent of your competitors.
I don't expect to win a foot race against Usain Bolt.
However, if I'm going up against my grandma, my chances of a win are a lot better. (I love you grandma, but you just don't have the spring in your step like you used to.)
How do you size up the competition in a writing contest?General Answer: Size matters.
A higher number of contestants means that there is a greater chance that there will be someone better than you. Everybody thinks they are above average, but the funny thing about averages is that when everyone thinks that, that becomes the new average. Unless you are truly excpetional, realize that a win in a crowd is a rare occurance.
Too add concrete numbers here - The Writer's Digest Competitions have thousands of contestants (buy a lottery ticket!), NYC Midnight Flash Fiction Contest runs around 400 (and in preliminary rounds, you are in groups of 20), most contests I enter have a few dozen to a few hundred entrants.
The frequency of the contest also plays a part. Is it held monthly (writerstype), quarterly (first line), or annually(wergleflomp)? Generally, the more often the competition is held, the wider the dispersion of contestants. On a down week (maybe summertime or Christmas) you may only be going up against a few others. Ad hoc contests can also be a way to go.
The reputation of the sponsor will attract the more reputable writers. A writing contest held by some obscure journal in the backwoods of your home state will offer a better chance at winning than going after the Pulitzer right off the bat.
If submissions are published, that's a great way to assess your skill against the other contestants. I realized I still have work to do when I read the entries for the NPR 3-minute Fiction contest.
A lot of the time, these variables will be unknown. So next time you don't win, just tell yourself that you were going against Stephen King (under a pen name of course).