General
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Non-obvious behaviors
gotchas
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General
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- `anova(model1
model2)`: F-test comparing nested models.
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Coding & Debugging
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- SANN (simulated annealing): convergence code is always 0 — it never fails. maxit = total function...
no other stopping criterion.
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General
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- Returns object with predict
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General
PromptBeginner5 minmarkdownQuality: 28
- Default method is Nelder-Mead (no gradients
robust but slow). Poor for 1D — use Brent or optimize().
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General
PromptBeginner5 minmarkdownQuality: 28
- predict.glm with type = response gives predictions on the response scale (e.g.
probabilities for logistic); type = link (default) gives on the link scale.
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General
PromptBeginner5 minmarkdownQuality: 24
- lowess parameter is f (span
default 2/3); loess parameter is span (default 0.75).
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General
PromptBeginner5 minmarkdownQuality: 24
- lowess is the older function; returns `list(x
y)` — cannot predict at new points.
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General
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- Direction: direction = both (default)
forward
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Creative
PromptBeginner5 minmarkdownQuality: 24
- Self-starting models (SSlogis
SSasymp
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Creative
PromptBeginner5 minmarkdownQuality: 28
- aov is a wrapper around lm that stores extra info for balanced ANOVA. For unbalanced designs
Type I SS (sequential) are computed — order of terms matters.
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General
PromptBeginner5 minmarkdownQuality: 24
- For Type III SS
use car::Anova() or set contrasts to contr.sum/contr.helmert.
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General
PromptBeginner5 minmarkdownQuality: 24
- Quasi-families (quasibinomial
quasipoisson) allow overdispersion — no AIC is computed.
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General
PromptBeginner5 minmarkdownQuality: 24
- binomial accepts response as: 0/1 vector
logical
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General
PromptBeginner5 minmarkdownQuality: 28
- `anova(glm_obj
test = Chisq) for deviance-based tests; F` is invalid for non-Gaussian families.
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General
PromptBeginner5 minmarkdownQuality: 28
- weights in glm means prior weights (not frequency weights) — for frequency weights
use the cbind trick or offset.
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General
PromptBeginner5 minmarkdownQuality: 24
- Column names from model.matrix can be surprising: e.g.
factorLevelName concatenation.
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General
PromptBeginner5 minmarkdownQuality: 24
- Common families: binomial(link = logit)
poisson(link = log)
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General
PromptBeginner5 minmarkdownQuality: 28
- Default family = gaussian(link = identity) — glm() with no family silently fits OLS (same as lm
but slower and with deviance-based output).
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General
PromptBeginner5 minmarkdownQuality: 28
- I() is required to use arithmetic operators literally: y ~ x + I(x^2). Without I()
^ means interaction crossing.
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General
PromptBeginner5 minmarkdownQuality: 24
- terms object attributes: order (interaction order per term)
intercept
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Creative
PromptBeginner5 minmarkdownQuality: 28
- model.matrix creates the design matrix including dummy coding. Default contrasts: contr.treatment...
contr.poly for ordered.
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General
PromptBeginner5 minmarkdownQuality: 24
- Captures output from cat
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General
PromptBeginner5 minmarkdownQuality: 24
Non-obvious behaviors
gotchas
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