BIO 330 Lab Quiz 2 Flashcards
analysis of variance tests
the null hypothesis that all groups/treatments have equal population means Ho: µ1 = µ2 = µ3 = ……
ANOVA compares
2 estimated components of variation MS_error, MS_groups
MS_error
Error mean square variation among samples in the same group- variance within group also MS_within
MS_group
Group mean square variation among samples that belong to different groups- variance between groups also MS_between
in null hypothesis is true
MS_error and MS_groups should be ~same F-ratio ~1
F-ratio
MS_groups : MS_error
MS_groups >> MS_error
F-ratio > 1 significant differences among the populations means, null hypothesis of no difference can be rejected
MS_groups not significantly larger than MS_error
null hypothesis cannot be rejected
ANOVA results p ≤ 0.05
at least one group differs from the others, does not tell us which group differs
If p ≤ 0.05
use post-hoc tests to find out which groups are significantly different from which others ex. Tukey-Kramer test
Squirrel study
red squirrel litter size decline w/ density due to: -reduced per capita food availability reduces fecundity -increased territorial interactions among individuals reduce surplus energy for reproduction
explanatory variables in squirrel study
Treatments- squirrel removal, food addition, habitat type
what were the levels of each treatment variable
squirrel removal (add, control) food addition (add, control) habitat type (douglas-fir, lodgepole pine)
ANOVA
Analysis Of VAriance
ANOVA uses what distribution
F-distribution to assess whether the calculated F-ratio is significant
t =
square root of F
simplest case of ANOVA
one-way/single factor ANOVA k ≥ 3, k = # of groups to compare 1 response variable, 1 treatment variable
response variable
litter size
is pseudoreplication an issue
there were multiple litter size measurements for each treatment, if we used every one that would be pseudoreplication, each of these points within one group are subsamples, we had to average them within each group
how to enter data
each column is a factor (treatment and response) each factor is coded (1,2)
How to run ANOVA
Stat- ANOVA- GLM- fit general linear model- resonse- mean litter- factors- habitat+food+squirrel model- all singles and combinations graphs- 4 in 1 storage- residuals
options dialog box
enter adjusted (type 3)
comparisons dialog box
enter pairwise comparisons activate Tukey, CL, test dialog boxes, post hoc?
is there any point in doing a post hoc?
if there are only 2 levels than probably not