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Rights Statements InC/1.0 , Open Access
Journal article
Statistical Power Comparison of Two Sampling Protocols for Riverine Snails
Northwest science., Vol.79, pp.91-98
2005
Handle:
https://hdl.handle.net/2376/649
Abstract
We compared the statistical power of two alternative sampling designs to detect changes in threatened and endangered snail species populations in the Mid-Snake River (Idaho). Our goal was to determine which sampling approach would have the best chance of detecting a change associated with different hydroelectric project management scenarios. We summarized the data as 1) the average number of snails collected across quadrats (density/m2) and 2) the proportion of quadrats that had snails present. We calculated the minimum detectable difference that each measure could detect with a two-sample t test. The density measure was highly variable and even a complete loss of snails failed to represent a statistically significant change for most sites. The precision improved somewhat when density was log-transformed, the number of replicate quadrats was increased, and larger sampling quadrat used; however, statistical power to detect change remained low. In contrast, proportion measures were much more precise and could detect a 34% reduction in the proportion of quadrats with snails present. When the number of quadrats was increased to 30, a 24% change could be detected and for 50 quadrats an 18% change. Proportion of quadrats with snails present was also highly correlated with the average density of snails (Pearson’s r = 0.91). In addition to being a more sensitive indicator, the proportion measure is quicker to observe for each sample which means that a larger area can be surveyed during the same amount of time.
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Details
- Title
- Statistical Power Comparison of Two Sampling Protocols for Riverine Snails
- Creators
- Leska S. Fore (Author)William H. Clark (Author)
- Publication Details
- Northwest science., Vol.79, pp.91-98
- Academic Unit
- Northwest Science
- Publisher
- WSU Press
- Identifiers
- 99900501717901842
- Copyright
- In copyright ; openAccess ; http://rightsstatements.org/vocab/InC/1.0/ ; http://purl.org/eprint/accessRights/OpenAccess
- Language
- English
- Resource Type
- Journal article