Guideline 8: Estimation of Measurement Error 



The process of collecting, transporting, and analyzing ecological data generates errors that can obscure the 

 discriminatory ability of an indicator. Variability introduced by human and instrument performance must be 

 estimated and reported for all indicator measurements. Variability among field crews should also be 

 estimated, if appropriate. If standard methods and equipment are employed, information on measurement 

 error may be available in the literature. Regardless, this information should be derived or validated in 

 dedicated testing or a pilot study. 



Guideline 9: Temporal Variability - Within the Field Season 



It is unlikely in a monitoring program that data can be collected simultaneously from a large number of sites. 

 Instead, sampling may require several days, weeks, or months to complete, even though the data are 

 ultimately to be consolidated into a single reporting period. Thus, within-field season variability should be 

 estimated and evaluated. For some monitoring programs, indicators are applied only within a particular 

 season, time of day, or other window of opportunity when their signals are determined to be strong, stable, 

 and reliable, or when stressor influences are expected to be greatest. This optimal time frame, or index 

 period, reduces temporal variability considered irrelevant to program objectives. The use of an index period 

 should be defended and the variability within the index period should be estimated and evaluated. 



Guideline 10: Temporal Variability - Across Years 



Indicator responses may change over time, even when ecological condition remains relatively stable. 

 Observed changes in this case may be attributable to weather, succession, population cycles or other natural 

 inter-annual variations. Estimates of variability across years should be examined to ensure that the indicator 

 reflects true trends in ecological condition for characteristics that are relevant to the assessment question. 

 To determine inter-annual stability of an indicator, monitoring must proceed for several years at sites known 

 to have remained in the same ecological condition. 



Guideline 11: Spatial Variability 



Indicator responses to various environmental conditions must be consistent across the monitoring region if 

 that region is treated as a single reporting unit. Locations within the reporting unit that are known to be in 

 similar ecological condition should exhibit similar indicator results. If spatial variability occurs due to regional 

 differences in physiography or habitat, it may be necessary to normalize the indicator across the region, or 

 to divide the reporting area into more homogeneous units. 



Guideline 12: Discriminatory Ability 



The ability of the indicator to discriminate differences among sites along a known condition gradient should 

 be critically examined. This analysis should incorporate all error components relevant to the program 

 objectives, and separate extraneous variability to reveal the true environmental signal in the indicator data. 



Phase 4: Interpretation and Utility 



A useful ecological indicator must produce results that are clearly understood and accepted by scientists, 

 policy makers, and the public. The statistical limitations of the indicator's performance should be 

 documented. A range of values should be established that defines ecological condition as acceptable, 

 marginal, and unacceptable in relation to indicator results. Finally, the presentation of indicator results should 

 highlight their relevance for specific management decisions and public acceptability. 



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