probability and significance

Question 1

What is probability?

Answer 1

the measure of the likelihood that a particular event will occur
> 0 indicate statistical impossibility
> 1 indicate statistical certainty

Question 2

What is a significance level?

Answer 2

the point at which researchers can claim to have discovered a large enough difference or correlation within the data to claim an effect has been found

Question 3

What is the usual level of significance in psychology?

Answer 3

• 0.05 = 95% certain that results are not down to chance
• p≤0.05

Question 4

Why is the level of significance 0.05?

Answer 4

psychologists can never be 100% certain about a particular result as they have not tested all members of the population under all possible circumstances

Question 5

When may a more stringent level of significance be used?

Answer 5

studies where they may be a human cost> drug trials
one off studies that could not for practical reasons be repeated in the future

Question 6

What is a type 1 error?

Answer 6

• false positive
• When the researcher rejects the null hypothesis and accepts the alternative hypothesis when it should be the other way round

Question 7

What is a type 2 error?

Answer 7

• false negative
• When the researcher accepts the null hypothesis and rejects the alternative hypothesis when it should be the other way round

Question 8

When are researchers more likely to make a type 1 error?

Answer 8

when the significance level is too lenient (too high) e.g. 0.1 10%

Question 9

When are researchers more likely to make a type 2 error?

Answer 9

when the significance level is too stringent (too low) e.g. 0.01 1%

Question 10

What statistical tests require the calculated value to be equal to or more than the critical value to be significant?

Answer 10

statistical tests with the letter R in them
- unrelated t-test
- related t-test
- pearsons r
- spearman’s Rho
- chi squared