PROBABILITY & SIGNIFICANCE

THE NULL HYPOTHESIS → there is no difference in what we are testing

THE ALTERNATIVE HYPOTHESIS → directional or non-directional. There is a difference in what we are testing

SIGNIFICANCE → tells us how sure we are that a difference or correlation exists. A ‘significant’ result means that the null hypothesis can be rejected

p < 0.10

p < 0.05 (psychology)

p < 0.01 (medical research)

p < 0.05 → there is a probability of equal to or less than 5% that the results are due to chance

~DETERMINING SIGNIFICANCE~

→ Once the statistical test has been completed, we will have a calculated value (e.g. S=3 for the sign test)

→ Compare this value to critical values table

→ This tells us whether the results we have are due to chance or due to the change in IV

~TYPE 1 ERROR~

→ Null hypothesis is rejected but it should have been accepted (instead of the alternative)

→ False positive - there isn’t a difference but they said there is one

→ More likely to be made when using a p = 0.1 significance level

~TYPE 2 ERROR~

→ Alternative hypothesis is rejected but should have been accepted (instead of the null)

→ False negative - there is a difference but they said there isn’t

→ More likely to be made when using a p = 0.01 significance level