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Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Estimation of uncertainty in status class assessment for Wel waterbodies Jannicke.

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Presentation on theme: "Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Estimation of uncertainty in status class assessment for Wel waterbodies Jannicke."— Presentation transcript:

1 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Estimation of uncertainty in status class assessment for Wel waterbodies Jannicke Moe (NIVA) deWELopment project meeting , Warszaw

2 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund From the deWELopment project description: Third phase: from single metrics to BQE-level assessment We will test different methods of combination of these single metric results to obtain a total result at the whole element level, taking into account the uncertainty in the different single metrics In our project we will test alternative approaches [ to the one-out-all-out principle] using different methods –simple averaging, weighted averaging, multimetric approach

3 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund From the deWELopment project description: Fourth phase: from BQE-level to waterbody-level assessment Testing different ways of combining the assessment results for different BQEs into one final result for the whole waterbody. –Here the recommended by one-out-all-out rule will be compared to other alternative methods. The risk of misclassification will be estimated –software STARBUGS (  WISERBUGS)

4 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Outline Uncertainty and risk of misclassification at BQE level Integration of uncertainty from BQE level to waterbody level WISERBUGS tool: examples with deWELopment results Next steps

5 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Uncertainty and risk of misclassification at BQE level

6 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Uncertainty: "accuracy" vs. "precision" High accuracy, but low precision –"roughly right" High accuracy and high precision –optimal result Low accuracy, but high precision –"precisely wrong" metric True value metric True value metric True value We can never know the ”true value”of a BQE metric – only the measured value Standard Deviation (SD) is a measure of precision, not accuracy

7 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Uncertainty in BQE level If we can never know the ”true value” of a BQE metric – how can we say something about uncertainty??? We must assume that the measured mean value represents the true value and the true status class We can assume that measured metric values follow normal distribution due to sampling uncertainty We can let measured SD represent sampling uncertainty Example: Measured metric values: 3, 5, 5, 6, 6 Mean: 5 Standard Deviation: 1.22

8 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Risk of misclassification - BQE level With the given mean and SD, we can test: if we re-sample the BQE many times, how often will we get the ”true” status class? Assuming that measured status class = true status class Risk of misclassification: = proportion of ”new samples” which result in wrong status class = 0.7% + 20% + 20% + 0.7% = 41.4%

9 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Risk of misclassifcation increases with SD -Higher SD gives flatter distribution => higher probability that new BQE values fall outside the true class Example: -SD increases from 1.0 to 1.5 -Probability of misclassification increases from 32% to 50% -”True class” is Moderate, but 25% probability that new samples will result in Good or High

10 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Risk of miscl. increases near class borders -If the measured mean BQE is close to a class border, then new BQE values are more likely to fall into a neighbour class Example: -Mean BQE decreases from 5 to 4.2 -Probability of misclassification increases from 32% to 46% -”True class” is moderate, but 42% probability that new samples will result in Good or High

11 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund How can we obtain SD for BQE level? Can we get reliable SD estimates from deWELopment data? –Many samples are needed per BQE and waterbody – we have ”only” 1-2 samples per BQE and waterbody (?) –Metric values are not necessarily normally distributed Other distributions can be considered What are the alternatives? –”Use best-available information from replicated sampling studies on environmentally similar waterbodies” (WISER data?) –Use best guesses –(Ask WISER WP6.1 for advice)

12 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Integration of uncertainty from BQE level to waterbody level

13 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Macroinvertebrates Phytobenthos Hydrology Acidification Organic Combining metrics and BQEs

14 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Two issues: 1)How to combine status classes for different metrics and BQEs Average; weighted average; all-out-one-out; etc. Will not be discussed here (see my presentation June 2010) 2)How to combine uncertainty from different metrics and BQEs Tool: WISERBUGS Combining metrics and BQEs

15 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund WISERBUGS – brief introduction WISER Bioassessment Uncertainty Guidance Software Excel-based tool developed within EU project WISER Purpose: assist in quantifying uncertainty in the assessment of ecological status of waterbodies Can be used for testing impact on classification of: –Combination rules for metrics and for BQEs –Class boundaries and reference conditions –Sampling uncertainty – SD (per metric) –Sorting/identification uncertainty – SD (per metric) –Uncertainty in reference condition – SD (per metric) Can not be used for –estimating SD for metrics (must be done separately) –estimating type I/II errors (because true status class is not known)

16 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund WISERBUGS – brief introduction WISERBUGS output: probability of each status class for... each waterbody (overall assessment) each BQE within a waterbody each metric within a BQE

17 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund WISERBUGS – brief introduction WISERBUGS input For each metric: –Measured value for each sample in each waterbody –SD representing sampling variation –Class boundaries (H/G, G/M, M/P, P/B) –”E1”: metric value for which EQR = 1 (Reference value) –”E0”: metric value for which EQR = 0 (bottom of metric scale) –(SD representing sorting/identification variation) –(SD for reference value) For overall assessment: –Combination rules for metrics within BQE –Combination rules for BQEs within waterbody –(Correlation between metrics)

18 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund WISERBUGS tool: examples with deWELopment results

19 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Data received from deWELopment Selected metrics: –Rivers: MP: River Macrophyte Index PB: Multimetric Diatom Index for rivers MI: Benthic Macroinvertebrate Index FI: European Fish Index + –Lakes: PP: Chlorophyll a; Phytoplankton Metric for Polish Lakes MP: Ecological State Macrophyte Index PB: Diatom Index for Lakes MI: Benthic Quality Index based on Chironomid Pupal Exuvial Techn. FI: Fish Index 'Summ Best’ (no class boundaries yet)

20 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Data received from deWELopment Metric values: –13 rivers + 10 lakes –Usually all BQEs for each waterbody Standard deviations per metric: not available –Randomised values used for this excercise –(To be discussed) Class boundaries and reference conditions (”E1”) per metric: –Sometimes waterbody-specific (OK for WISERBUGS) ”E0” – given in correct scale?

21 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Metric specification - 1 (Lakes) Class boundaries Metric names Other details

22 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Metric specification - 2 (Lakes) Other types of variation SD from sampling variation NB: SD values are made up!

23 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Metric specification - 3 (Lakes) Grouping of metrics by pressure within BQE Grouping of metrics by BQE

24 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Metric specification - 4 (Lakes) Weighting of each BQE Rule for combining BQEs within waterbody (here: one-out-all-out) Rule for combining metrics within BQE

25 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Results: assessment for individual metrics NB: Fake SD values - results must not be interpreted as real.

26 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Results: assessment combined per BQE and per waterbody Combination rule for total assessment: ”worst case” (all 4 BQEs)

27 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Results: assessment for BQEs and waterbody Combination rule for total assessment: ”average” (all 4 BQEs)

28 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Next steps

29 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Next steps for data analysis Try to obtain SD estimates / best guesses from BQE groups Quality-check of class boundaries, E0, E1 etc. –Confusion EQR scale vs. original metric scale? Explore impact on classification of... –different level of uncertainty (sampling SD) –different combination rules –etc. –what is most useful for deWELopment? Estimate risk of misclassification for selected cases –”True class” will be determined by the given metric values, and an agreed set of SD and combination rules Include physico-chemical parameters in assessment? Other suggestions?

30 Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Publication 1 manuscript on exploring risk of misclassification using the metrics and classification system developed by deWELopment and the WISERBUGS tool Potential co-authors –BQE group leaders ? –Gosia ? –Coordinators: Hanna and Anne (or acknowledgement?) –WISERBUGS author: Ralph Clarke (or acknowledgement?)


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