Dear Alejandro,

The EQR is the conversion equation that you need!! Actually, the EQR is not a real index. You can use it to turn the results of the application of an index (any index you need!) in a 0-1 scale, where 0 is the worst condition and 1 is the reference condition (pristine lake or river or...). Example. You have the index "A" and the index "B". The "A" index, applied to 10 rivers range between 1 and 10. The "B" index range between 1 and 100. If in the river "X" you have A=6 and B=40, the EQR of the first index (A) is:

EQR(A)= 6/10=0.6

and, of course, the EQR for B is:

EQR(B)=40/100=0.4

Than the two index (A and B) give you two different aswers. The A index (if you calibrated the EQR on the worst and the best condition) tell a story of good status of conservation. The B index of a poor status.

That's the simply way. You can find some other information reading the

"Guidance document on the intercalibration process 2008-2011." of the European Commission (CIS, 2011).

Take a look to it, because the "linear" application to the EQR is possible only if the indices have a "linear" response to the ecological degradation.

Thank you Mattia,

but I work with both linear and logarithmic indices, which also vary at different slopes depending on how close they are from the "High" status, also they represent ecological quality inversely (from 6-->0, and from 0.3-->0, being 0 the highest!), might it require some extra concoction? or can I use just:

EQR = 1 - (value/maximum) ?

Hi Alejandro,

The BOPA index ranges from 0, when there are no opportunistic polychaetes, to 0.30103, when there are only opportunistic polychaetes reflecting the most disturbed situation”, then you can use the next formula to obtain EQR.

EQR= (0.30103-BOPA)/0.30103, when BOPA= 0.30103 EQR=0, when BOPA=0 EQR=1

AMBI, I don't remember if maximum value is 6 or 7,

EQR=(6-AMBI)/6

Gracias Jose! ahora puedo normalizar los valores y estudiar la sobreestimación con mayor precisión

The solution suggested by Jose De-la-Ossa-Carretero it's ok!

To conclude, I seggest you to be "chary" (I hope it's the correct word in English) when you'll discuss the results of your comparison, expecially for the "central part" of the scale and the thresholds between "moderate" and "good", that is also the difference between "The system is ok" and "The system needs some actions... some money".

Does anyone know the reference (paper or document) where I could find José's answer?

Thanks.