Comparative Analysis Results for North American Breeding Bird Survey Using Estimating Equations and Hierarchical Models
These tables provide a comparative summary of Estimating Equations (Link and Sauer 1994) and Hierarchical Model (Link and Sauer 2002) trend analysis results. This information is provided as a supplement to a recent paper comparing the methods(Sauer and Link, In Press), and is intended as a resource for users who are interested in more detailed comparisons of results from the historical analysis method (Estimating Equations) and the Hierarchical Model analysis method. The Hierarchical Model will be used as the primary BBS analysis method starting in 2009. Please see Sauer and Link (In Press) for an overall summary of the differences between the analyses and for a rationale for use of the Hierarchical Model analysis.
Here, we present trend analysis results for both analysis methods for the long-term (1966 - 2008), and present a 10-year trend analysis and long-term annual indices from the Hierarchical Model analysis. Population trend estimates are the simplest measure of population change over a time period. They are expressed as a percent change per year, and in these Tables they are presented for Bird Conservation Regions, states, Provinces, and survey-wide.
Here is a sample Table. Numbers above the headers are described in detail below:
(1) Region Name: Regions include Bird Conservation Regions (BCRs, presented first), states and Provinces within which the species occurs, and the entire survey area. Note that the region names are links. Clicking on the region name will display a graph of annual indices of populations for that species in the region.
(2) Column N: The number of survey routes on which the Estimating Equations method could be applied. This number is typically smaller then the total number of routes on which the species occurred, as the estimating equations method requires sufficient samples on a route to estimate a change (Link and Sauer 1994).
(3) Column D: This column provides an indicator (A) if the estimating equations result is smaller than the Hierarchical Model results, or (B)if the estimating equations result is larger than the Hierarchical Model results. Comparisons are based on overlap of Credible Intervals (CIs).
(4) Column V: This columns provides an indicator if the Hierarchical Model result is imprecise, as measured by a half-width of the CI >3.
(5) Hierarchical Model results for the interval 1966 - 2008, presented as percentage change per year (%/Yr), along with 2.5% and 97.5% credible intervals. The significance of the result is assessed by evaluation of whether the CI includes 0.
(6) Estimating Equation Results for the interval 1966 - 2008, presented as percentage change per year (%/Yr), along with 2.5% and 97.5% confidence intervals.
(7) Hierarchical Model Results for the interval 1998 - 2008, presented as percentage change per year (%/Yr), along with 2.5% and 97.5% credible intervals.
(8) Percentage of species range occurring in the BCR, as summarized by supplemental materials in Punjabi et al. (2005). Note that these values are only available for a subset of species, and if they are not available all values will be 0 in the column.
(9) Conservation concern status in the BCR, as summarized by supplemental materials in Punjabi et al. (2005).
Link, W. A., and J. R. Sauer. 1994. Estimating equations estimates of trends. Bird Populations 2:23-32.
Link, W. A., and J. R. Sauer. 2002. A hierarchical model of population change with application to Cerulean Warblers. Ecology 83:2832-2840.
Panjabi, A. O., E. H. Dunn, P. J. Blancher, W. C. Hunter, B. Altman, J. Bart, C. J. Beardmore, H. Berlanga, G. S. Butcher, S. K. Davis, D. W. Demarest, R. Dettmers, W. Easton, H. Gomez de Silva Garza, E. E. Iñigo-Elias, D. N. Pashley, C. J. Ralph, T. D. Rich, K. V. Rosenberg, C. M. Rustay, J. M. Ruth, J. S. Wendt, and T. C. Will. 2005. The Partners in Flight handbook on species assessment. Version 2005. Partners in Flight Technical Series No. 3. Rocky Mountain Bird Observatory website: http://www.rmbo.org/pubs/downloads/Handbook2005.pd
Sauer, J. R., and W. A. Link. In Press. Analysis of the North American Breeding Bird Survey using hierarchical models. The Auk.