1. Question-Bank 1g – Tukey/Dunnett tests @UWE_KAR
Practice & Communication of Science
Question-Bank
1g – Tukey/Dunnett tests
@UWE_KAR

2. So your ANOVA is sig: is that it?
1-way, 2-way/factorial ANOVA
can deal with one (1-way) or two (2-way) factors
and produces a single p-value for each factor
eg Q1 from the anova.docx q-bank
two factors (temp and inoculum dose)
each has a p-value (0.071 and 0.000)
so temp is non-sig and does is sig
but dose has 4 levels!
how do I apply this single p-value to the pattern of results within the levels? (called post hoc testing)
One approach (great for exams!) is the Least Significant Difference
but there are others…

3. Post Hoc Tests and ANOVA
Least Significant Difference
tells you how far apart any pair of means (ie two levels of a factor) need to be to be significant
Tukey
Similar to the LSD, the Tukey test can test all levels against each other
levels to be compared with each other are identified and referred to as a ‘family’
for that ‘family’, you make the confidence level for the many individual comparisons stricter so overall ‘family’ level is 95%
it’s automated in Minitab
and not suited to calculation in an exam! 

4. Post Hoc Tests and ANOVA
Dunnett test
used where one level is obviously a ‘control’ or ‘reference’ level
comparisons will then be made between this control and each of the other, ‘experimental’ levels
the test creates CIs for differences between mean of each ‘expt’ group and mean of ‘control’ group
if a CI contains 0, then no significant difference
remember, 0 is the Null Hypo so if 0 is in the CI then it (the Null Hypo) is not unusual and can’t be rejected
as before, multiple comparisons means that individual confidence levels are increased so overall ‘family’ confidence level is appropriate (95%)
like Tukey, it’s automated in Minitab and not suited to calculation in an exam! 