1. Session 1d Selecting appropriate thresholds
Introduce Shiny app
Link is in Guidance Manual
Participants to have a go
Run through values
Summarise results using Fig 2-1

2. Making life easier for ourselves: the Shiny app
Start by clicking on “Import and Preprocess”

3. Browse your files to find the one you need …
… or click here to use the example dataset

4. Select appropriate separator and decimal symbols

5. Possible boundary values for L-CB1
You have generated a number of possible boundary values
Differences between methods
Decisions regarding outliers
Decisions regarding linear range

6. Possible boundary values for L-CB1
Output from regression methods:
Output from categorical methods:
Output from mismatch method (GM only):

7. Potential boundary values for L-CB1 (summarised as g L-1 TP)
Method
Lower
Centre
Upper
OLS1 57 87
RMA 50 73
OLS2 36 53
Average medians
Average quartiles 54
75th quartile
mismatch 51
Logistic regression 56 79
Range of national boundary values (Table 4-4 from CIS Guidance Manual)
25th percentile 33
Median 60
75th percentile 62

8. Regulation options (a) intersection with best-fit line
(b) upper confidence line
(c) lower confidence line
Horizontal line shows the biological good/moderate boundary (0.7 in this example); vertical lines show intersection with regression line ± confidence intervals marking potential good/moderate boundary values for total phosphorus .
Triangles mark areas where classification mismatches occur, green (biology good but phosphorus moderate) and yellow (biology moderate or worse but phosphorus good) using three different approaches to interpretation.

9. Regulation options
Action (e.g. programme of measures) is triggered as soon as the nutrient boundary is exceeded (“one out, all out”).
a higher boundary value may be appropriate, to minimise the instances in which elevated nutrient concentrations trigger measures despite biology being at good status (i.e. Figure 2‑1b).
Additional considerations that should be made before measures are implemented include current proximity to the good/moderate (G/M) boundary for sensitive BQEs, likely trends in nutrient concentrations if no action is taken and whether there are other factors that might reduce the sensitivity to nutrients (e.g. shade, high flow, grazing, toxic substances).
Exceedance of the nutrient boundary is one of a number of strands of evidence that are considered before a programme of measures is triggered.
A more precautionary (lower-concentration) boundary value may be selected (e.g. Figure 2‑1c); however, the regulator would then check that that a nutrient-sensitive BQE was also failing in the water body under consideration prior to taking action, or that there was evidence that it might do so in the future (e.g. if there was a trend of increasing nutrient concentrations, or the likelihood of an increased sensitivity to nutrients due to climate change, removal of shade, lower flow or reduced grazing pressures).

10. Potential boundary values for L-CB1 (summarised as g L-1 TP)
Method
Lower
Centre
Upper
OLS1 57 87
RMA 50 73
OLS2 36 53
Average medians
Average quartiles 54
75th quartile
mismatch 51
Logistic regression 56 79
Range of national boundary values (Table 4-4 from CIS Guidance Manual)
25th percentile 33
Median 60
75th percentile 62