What Click Through Rate Curve Do You Use?

We use a click through rate (CTR) curve to calculate our estimated traffic and estimated opportunity metrics. We have created a model based on various data inputs that we use for our calculation:

Ranking Postion	Click Through Rate
1	30%
2	22%
3	14%
4	10%
5	8%
6	6%
7	4%
8	3%
9	2%
10	2%
11	1%
12	1%
13	1%
14	1%
15	1%
16	1%
17	1%
18	1%
19	1%
20	1%