Schedule estimates, take 1

At work, we're planning a big project. I handed a coworker a batch of specs and asked him to estimate how long it would take a writer to document the features described. I made my own very crude calculation, trying to pad the numbers a bit to compensate for my known tendency towards optimism.

I came up with an estimate of x writer-weeks. My coworker came up with an estimate of 3x writer-weeks. Head, I'd like you to meet Desk. I know you'll get along famously.

I'm tempted to split the difference and turn in an estimate of 2x writer-weeks. But what I probably need to do is go back and re-examine the assumptions I used in my back-of-the-envelope calculation.