TRIM - frequently asked questions
FAQ TRIM
- Adding a new year to the data results in changes of indices in earlier years. Is that correct?
- Are there any requirements to the data?
- How can you see if the model fits?
- How should one assess the best fitting model in case of overdispersion and/or serial correlation?
- How to interpret the overall trend?
- How to interpret the standard errors of indices?
- Is it possible to name the categories within a covariate?
- Is it possible to open outputfiles generated in earlier TRIM runs?
- Is it possible to put all species data in one file and then assess indices for all species in one run?
- Is it possible to test the significance of change between two years?
- Is it possible to treat monthly and yearly data simultaneously?
- Is lack-of-fit of the model relevant in case there are few missing counts?
- Is there any lower limit in the number of sites to be meaningful? Not really, but few sites will usually result in large standard errors of the indices and trends.
- TRIM - frequently asked questions
- TRIM generates additive and multiplicative parameters. Which are to be preferred?
- TRIM generates model indices as well as imputed indices. Which are to be preferred?
- What are the advantages of incorporating covariates in the model?
- What do error messages mean as "model error: zero observations for changepoint at time 3"?
- What do error messages mean as "model error: zero observations for changepoint at time 3, category 1"?
- What do the error messages "invalid floating point operation", "singular matrix", "diverging parameters" mean?
- What does the error message "too many parameters" mean?
- What does the error message "unexpected value site." mean?
- What if the data are not Poisson distributed?
- What if the model does not fit?
- What is a covariate?
- What is overdispersion and what is its impact on the indices?
- What is the impact of serial correlation on the indices?
- What is the meaning of the 20-year period in Appendix C in the TRIM manual concerning the overall slope?
- What is the meaning of the stepwise procedure to select change points?
- What is the meaning of the Wald test for significance of deviations from linear trend?
- What is the use of the "no time effects model"?
- Which model should one use: the time-effects model or the linear trend model?
- Which proportion of missing values in the data is allowed?
- Which year should be chosen as the base time year?
- Why are the default p-values in the stepwise selection 0.2 and 0.15 instead of 0.05?
- Why has no bootstrapping being applied to assess standard errors of indices?