23 Feb 09 Dear Dame

This question is a great one that confuses many – even the Wikipedia page it references could be made a little clearer…. maybe in my spare time I’ll update it

“This information was referred to me but it has sort of confused me more. Its called The Hotel Problem. http://en.wikipedia.org/wiki/Web_analytics

I understand what it is saying but why doesn’t it apply to First Time Unique visitors which gives you the same total for the month in comparison to adding up the value for every individual day?

It will explain how Prior Unique Visitors is different depending on the date range.

Any further thoughts?”

This is a common question and basically it comes down to the measure of “uniqueness”.

Prior unique visitors seems to be a “return unique visitor” while the Ffrst time unique visitor is an absolute unique visitor.

Your total unique visitor count should be a combination of Prior Unique Visitors and First Time unique visitors.

If you look at the table below;

 

Day	1	2	3	4	5	6	7	8	9	10
Visitor A	1		1		1		1			1
Visitor B		1				1				1
Visitor C			1		1				1

Then you get this result,

FTUV	1	1	1	0	0	0	0	0	0	0
PUV	0	0	1	0	2	1	1	0	1	2
TUV	1	1	2	0	2	1	1	0	1	2

When you look over different time period and add these visits together you see a lot of variance that seems contradictory.

1 Day granularity	10 Day Granularity
3	3
8	0
11	3

FTUVs will never change with granularity because a visitor can only be new to your site once (unless they delete a cookie, and then they are a new visitor).