Parametric Criteria - Methods

notes on parametric tests criteria for methods

a2 psychology with aqa

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  • Created on: 29-06-12 13:44
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Parametric criteria
Statisticians describe parametric tests as powerful
For a parametric test to be used the following 3 criteria must be met:
1. Interval data
2. Normal distribution
3. Homogenous variances or homogeneity of variance
1. Interval data
The level of measurement must be interval
2. Normal distribution
Data should be normally distributed or at least drawn from a population which would be expected to
show a normal distribution for whatever variable is being measured
We can check for normal distribution by considering the following:
Frequency distribution graph (`bell' shaped)
Mean, mode and median should be similar
By eye
3. Homogenous variance
Basically, this means that two sets of scores should have a similar spread around the mean
This can be determined by calculating either the range or standard deviation for two sets of
Statisticians describe parametric tests as `robust'
This means that they can cope with data that doesn't fully meet the 3 criteria
The only criterion that absolutely must be met is that of interval data


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