Trends

Tim Gerrodette and John Brandon
Southwest Fisheries Science Center
La Jolla, California, USA

TRENDS is a program designed to carry out a power analysis of linear regression, particularly in the context of monitoring populations in wildlife studies. TRENDS summarizes the power analysis in 5 parameters: duration of study, rate of change, precision of estimates, alpha (type 1 error rate), and power (1-beta, where beta is the type 2 error rate). The value of any one of these can be estimated if the other 4 are specified. The relationships among these are affected by several other parameters, such as whether the change is linear or exponential, whether the change is positive or negative, whether the statistical test is one- or two-sided, and how the precision of the estimates depends on abundance. Thus, TRENDS is designed to help answer such questions as: How many years are required to detect a trend? How large is the rate of change that can be detected? What is the probability of detecting a trend (that is, of getting a significant slope to the regression line)?


Download TRENDS for Windows 95/98/2000/XP- Version 3.0
Download TRENDS for DOS- Version 3.0

After downloading the Windows version, run TrendSetup.exe to extract 4 compressed files. Open the TrendsReadMe.txt file and follow the installation directions. For Windows 7/8, use the following workaround. Download the setup.exe and the VFRUN61I.exe programs as directed above. This creates a Trends folder in Program Files (x86), but the code is looking for the TRENDDLL.dll file in the old 32-bit folder Program Files. The solution is to create a folder named "Trends" in the 32-bit folder "Program Files" and put the TRENDDLL.dll file in it. Then the executable file (Trends.exe) should be able to run from any location on your computer.

A manual for version 3.0 is not yet available, but a user's guide for an earlier DOS version can be downloaded.

References
Gerrodette, T. 1987. A power analysis for detecting trends. Ecology 68: 1364-1372
Gerrodette, T. 1991. Models for power of detecting trends - a reply to Link and Hatfield. Ecology 72: 1889-1892.
Gerrodette, T. 1993. Trends: software for a power analysis of linear regression. Wildlife Society Bulletin 21: 515-516.

Send questions or comments to tim.gerrodette@noaa.gov

TRENDS will continue to evolve. If you would like to be notified of new versions in the future, please email your name to the address above.

 

Last modified: 10/30/2015