Don't confuse an adjectival label (sometimes called an attributive noun) ending in s with the need for a possessive.
Sometimes it's not easy to tell which is which. Do you attend a writers' conference or a writers conference? If it's a group of writers attending a conference, you want the plural ending, writers.
If the conference actually belongs to the writers, then you'd want the possessive form, writers'. If you can insert another modifer between the -s word and whatever it modifies, you're probably dealing with a possessive.
Additional modifiers will also help determine which form to use.
Patriots quarterback Drew Bledsoe threw three touchdown passes. (plural as modifier)
The Patriots' [new] quarterback, Drew Bledsoe, threw three touchdown passes. (possessive as modifier]
