Analysing variance and analysis of repeated measurements Flashcards

1
Q

What is the principle behind analysis of variance?

A

to partition the total variability of a set of data into components due to different sources of variation
systematic differences between the group means and
the variations between individuals within each group

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2
Q

What is the null hypothesis in one-way analysis of variance?

A

The is no difference been the groups and the test compares the observed variation between the groups with that elected from the observed variability between subjects

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3
Q

What are the assumptions underlying ANOVA?

A

the samples come from normally distributed populations with the same standard deviation
normality of residuals
independence

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4
Q

What is the problem of making multiple comparisons?

A

gives a high probability of a finding a significant difference just by chance

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5
Q

What is the bonferroni method?

A

a method of manual multiple testing
it is fine for up to 5 comparisons but is highly conservative
it adjusts the p value to account for multiple testing

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6
Q

Describe Tukey’s HSD

A

most sensible choice if you wish to consider all comparisons

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7
Q

Describe Dunnett’s

A

most sensible choice when you are only interested in comparing one group (e.g control) to each of the other groups. More powerful than Tukey’s in this situation

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8
Q

Describe Fisher’s LSD

A

not generally recommended. does not take multiple comparisons into consideration

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9
Q

What is different about the analysis of repeated measurements?

A

observations on the same subject just have some relationship between them, and are very likely to be correlated to each other. Data points are not independent

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10
Q

What are the problems with point by point analysis of repeated measurements?

A

ignores the correlation between successive observations from the same individual
may conceal important features of the data
causes a multiple testing problem
ignores the continuous nature of the underlying process

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11
Q

Give examples of summary measures that can be used for each subject’s series of measurements

A
maximum or minimum values 
time to maximum
area under the curve
mean
slope of straight line fir
last measure minus first measure
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