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Question:
I would like to know, if the assessment would be satisfactory, if I use an average value and thus use an exponential distribution or should I use the average + SD and use lognormal? An average value is an average of 12 samples taken each month through year from one monitoring place. So SD are calculated from 12 samples from one monitoring place and are not related to different places in specific
river. The assessment with average value without SD should represent satisfactory results compared to average + SD in my case? Dose rates should be in the same range when using exponential or lognormal?

Answer:
Easy art part of your question first - your mean estimate when using a mean and pdf in Tier 3 of the ERICA Tool will be similar to estimate using Tier 2 and inputting a mean value only; it will not be exactly the same as Tier 3 is probabilistic. The mean estimates using either a lognormal or an exponential distribution in Tier 3 will be similar. The percentiles, minimum and maximum values will be different and dependent on the SD used for the lognormal distribution.

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