Docstoc

Microsoft PowerPoint Viewer - ConfidenceIntervals_update5

Document Sample
Microsoft PowerPoint Viewer - ConfidenceIntervals_update5 Powered By Docstoc
					Confidence Interval around a Percentile (CIP): Impaired <10% of the time (EPA guidelines),
with 80% confidence (TCEQ currently controls Type I error at 20% on listing).
If the confidence interval (CI) region is below the maximum criteria value for a parameter,
or is above the minimum critera value for a parameter, the waterbody is not considered
impaired.

A waterbody is an impairment concern if the CI region overlaps the criterion
for the parameter of interest.

A waterbody is impaired if the CI region is above the maximum criteria value for a parameter,
or is below the minimum criteria value for a parameter.
H1 = There is less than a 20% chance of falsely impairing a water body that is supporting
the criterion 90% of the time (or 75% of the time for bacteria).




  26 Oct, 2004             TCEQ Austin, SWQM Stakeholders Meeting                      1
                 Various confidence intervals around a percentile...




                                                            50% C.I.




                                                                              50% C.I.
                                                 60% C.I.




                                                                                         60% C.I.
                                             70% C.I.




                                                                                                    70% C.I.
                                                                       90th




                                                                                                               80% C.I.
                                          80% C.I.




                                                                                                                          90% C.I.
                               90% C.I.
               Probability




                                                 Parameter value




26 Oct, 2004                 TCEQ Austin, SWQM Stakeholders Meeting                                                                  2
                                                                                    Start/finish
                                                                       80% C.I.                           FS
                                                                                          Criteria




                                                   Probability
                                   Delist
                                                                                   Parameter value
               NS       80% C.I.
                                                                                                                                80% C.I.               T2
                          90th                                        90th percentile                                             90th
Probability




                                                                                                               Probability
                                                                        Determining impairment
                             Parameter value                               by evaluating the                                         Parameter value
                                                                          Confidence Interval
                   NS            80% C.I.                              around a Percentile (CIP)
                                   90th                                                                                              80% C.I.          T2
     Probability




                                                                                                                                         90th




                                                                                                                Probability
                                 Parameter value
                                                                                                                                     Parameter value
                                                                     NS                      80% C.I.
                                                                                                90th
                                                       Probability




                                                                                                                              List


                                                                                        Parameter value
                                                                                    Start/finish
                                                                       80% C.I.                           FS
                                                                                          Criteria




                                                   Probability
                                                                                   Parameter value
               NS       80% C.I.
                                                                                                                              80% C.I.              T2
                          50th                                        50th percentile                                           50th
                                                                      (ie: median)
Probability




                                                                                                               Probability
                                                                          Determining impairment
                             Parameter value                                 by evaluating the
                                                                                                                                  Parameter value
                                                                            Confidence Interval
                                                                          around a Median (CIM)
                   NS            80% C.I.

                                   50th                                                                                           80% C.I.          T2
     Probability




                                                                                                                                       50th




                                                                                                                Probability
                                 Parameter value
                                                                                                                                  Parameter value
                                                                     NS                      80% C.I.
                                                                                                50th
                                                       Probability




                                                                                        Parameter value
                                          Summary




When a parameter is not currently listed, assess with recent data:
To avoid the expense and distraction of falsely listing a water body when it is not impaired,
the Type I error is currently controlled at < 20%

Missing an impairement: the Type II error is high for small samples, especially near the criteria.

Null Hypothesis: Not impaired
Alternate Hypothesis: Is impaired

When a water body is on the current list, assess with recent data:
To avoid delisting a water body when it it still impaired, the Type I error could be controlled at < 20%

Erroneously continuing the listing: the Type II error is high, especially near the criterion.

Null Hypothesis: Still impaired
Alternate Hypothesis: No longer impaired




26 Oct, 2004                 TCEQ Austin, SWQM Stakeholders Meeting                                  5

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:12/1/2011
language:English
pages:5