L6 Flashcards
Continuous forms of measuring data?
Interval - equal intervals
Ratio - had true zero
Formula for z score?
(Score - group mean)/group STD
Steps of hypoth testing?
- Assume null hypoth is true
- Fit a statistical model to the data that represents the alternative hypoth and see how well the model fits the data in terms of variance
- calc prob of getting that model if null was true
- If prob insig, then reject null
Values of Sd on normal curve
2sd = 95%
What is chi sq used for
Calc precisely prob of obtaining a given score
Estimates diff between observed and expected data
If chi sq is large enoug, then variables are associated
What’s in a contingency table?
Observed and expected values of variab,Es. And total
How do you calculate expected values?
( Row total x column total )/ total n of observations
How to calc chi sq?
X= sum of (observed - expected)^2 / expected
Do for every cell then add up
What’s a type 1 error?
Where we believe there is an effect in the population when there isn’t
How to calculate df?
Number of (n of rows - 1)(n of columns -1)
When is chi significant?
If value obtained is bigger than critical value (from table)
What’s an adjusted standardised residual?
Residuals tell you the direction of an association
Adjusted stNdarxised ones are standardised to equate to z score distribution
Spss does this
How to calculate residual?
Observed - expected = residual for a cell
Assumptions of chi sq?
Sample is drawn from pop randomly
Sample is large
Sample is greater than 5 in each cell
Observations are independent of eCh other
Why use fishers exact test?
Chi sq uses approximate distribution, which is not accurate if sample is small
Therefore if sample is small use fishers exact test
