I read somewhere (wish I could remember where so I could cite it) that a number of manufacturers are starting make their sizes larger due to the idea that Americans are ever expanding their waist size (for example, the article said that an average size six 10 years ago is closer to an eight now). Always try them on if its a brand you havent purchased in awhile. I went into buy a pair of shorts which I ALWAYS get an Xsmall and they were big on me, the guy at the LBS said a number of people suddenly seem to be dropping a size in their clothes. Of course there isnt anything smaller than an XSmall.
"Do or do not, there is no try" - Yoda