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Trend Analysis Form
1966 - 2002 Analysis
See the BBS Summary and Analysis Website for citation, version number, and cautions regarding use.
This part of the Home Page allows you to select a species, a region, and a starting and ending year, and the Home Page will conduct an analysis for that species, region, and period. Exercise caution in reviewing the results from this website, as it is often difficult to interpret BBS results without evaluation of information analyzed at multiple temporal and spatial scales. We identify a few limitations of trend data in our credibility measures discussion. Also note the disclaimer associated with all results.
Most of you realize that analysis of BBS data can be controversial. The survey covers such a large area that regional differences in number and quality of survey routes are inevitable. Also, the count data collected in the survey are only indexes to the population, and the proportion of animals counted can differ among routes and observers. For more information on these issues, visit our description of the BBS.
Consequently, there are many notions of how to analyze the data, and some of the differences in methods can provide quite different results. We provide 2 alternative procedures for analysis, a linear route-regression approach based on estimating equations, and a LOESS-based route-regression approach. We have compared the results of these analyses on the large (survey-wide) scale, and found that they provide generally similar results. If you want to see a summary of the comparison, and our opinions on which analysis to use, click here.
Occasionally, if a route is omitted from the regional analysis, a message will be printed. These can be ignored.
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ver 2000.0, 14 March 2001, Authors: J. R. Sauer and J. E. Hines.
Data Liability Disclaimer
Although these data have been processed successfully on a computer system at the United States Geological Survey (USGS), no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from a USGS server, and not indirectly through other sources which may have changed the data in some way. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The USGS shall not be held liable for improper or incorrect use of the data described and/or contained herein.
So, these data are provided "as is" and without any express or implied warranties, including, without limitation, the implied warranties of merchantability and fitness for a particular purpose. Also, use of trade names or commercial products in this home page is solely for the purpose of providing specific information, and does not imply recommendation or endorsement by the U.S. Government.