How far back would you allocate a conversion to a particular referrer? 15 days, 30 days, 60 days? How long do you let your cookies sit for?

I've been liaising with a company who offer a tracking service and asked them this question, here's their reply:

"...after a period of absence of 14 days or more, market analysis suggests they have forgotten your site and have come back again through due to seeing a new advert (if not book marked). If this is the case then the visitor will be re tagged and the sale allocated to the new search terms or referral page etc. This two week setting took a long time to establish and a lot of analysis and testing with a broad range of online retailers. It is now set at the optimum for online retail in the UK and is unchangeable as it provides provides the best results on this setting."

I've never seen or heard anybody else say this before - can anyone substantiate this? Don't Google use a 30-day cookie on their free tracking tool? What do Overture do? What do you do?

I think by Market Analysis, they mean their own research - problem is their client-list hasn't really got any big sites....

I'm not disputing this 'fact' per se but I've never heard this before and wondered what others thought about it...

Thanks

Cookies are essentially used to identify a unique visitor (although there are other uses for such two pair values). The length of the cookie would depend on your nature of business. A HR consultancy service provider would require a cookie length of atleast 30 days. An organisation seeking HR consultancy advice may plan a month in advance before any company policies/plans are implemented. Having gathered the information this searcher may return within 30days to subscribe to HR advice.

A shopping comparison engine on the other hand would require a cookie length of around a max of 7 days, though the merchant of the comparison may need somthing longer dependant on the nature of their business.

So the question to ask here is how long do your visitors need to consider their investment, and options to make that investment elsewhere.

So the question to ask here is how long do your visitors need to consider their investment, and options to make that investment elsewhere.

Nicely put. Thanks for your insight.