Top Slicing Relief Question

In calculating the average rate of tax paid for the last three years the following example is suggested in previous threads here and elsewhere:

Example:
Year earnings incomeTax paid
2009 €40,000 €13,000
2008 €38,000 €12,000
2007 €36,000 €11,000

Total €114,000 €36,000

Average tax rate is €36,000 ÷ €114,000 x 100 = 31.6%

A quick question: Is it valid to use the Effective Tax Rates from the Revenue assessments for the past 3 years to work out the Average tax rate in a Top Slicing Relief calculation?

Many thanks

If you have the assessments to hand then you have the income and tax figures already. Why would you want to calculate it a different way?

Mrs Vimes said:

If you have the assessments to hand then you have the income and tax figures already. Why would you want to calculate it a different way?

Click to expand...

Calculating it using an average of the Irish Effective Rates from Panel 4 of the previous 3 years assessments seems the most straightforward to me because although the income is totally clear on the assessment the income tax paid is not (due to reliefs, levies, etc).
So is it valid to use an average of the Irish Effective Rates from Panel 4?