Comparing Onclick and Onmousedown

[4specs]

Google uses onmousedown to track the clicks from their organic searches.

Google analytics uses onclick to track clicks going to outside websites.

When I ran both on links last year the onclick showed about 5-7% more clickthroughs.

Any ideas as to why there would be a difference? Which is preferred if you wanted to use one or the other to track referrals from the site?

I am using this to avoid a hard-coded 302 redirect script. I currently use a javascript rewrite to rewrite the href to a redirected href and am looking to simplify the code.

Thank you.

[Fotiman]

My thought is that onmousedown does not garantee that an onclick event will occur on the same target. For example, if you mouse over a link and then press and hold the click button, but then you move off of that link and release the button, the link will not be clicked.

Short answer: use onclick.