Probability And Significance

Question 1

Null vs alternative hypothesis

Answer 1

Null - there’s no significant difference/causal relationship between IV and DV, alternative hypothesis states there is

Question 2

Probability

Answer 2

Likelyhood of something occurring by chance

Question 3

The higher the probability the greater… so therefore …

Answer 3

likelihood the results were down to chance
Therefore, you want as low probability as possible.

Question 4

Significance level

Answer 4

The level of probability at which it is agreed that the null hypothesis will be rejected and the experimental hypothesis accepted.

Question 5

Usual level of sig

Answer 5

P<_ 0.05 (5%)
Probability that our results are due to chance is less than 0.05

Question 6

What is a type I error

Answer 6

Null hypothesis is rejected and alt hypothesis is accepted when it should have been other way round, null hypothesis is true (false positive - found. A correlation but it down exist)
More likely if significance level is too high (10% or 0.1)
Data collected has passed significance level but really the findings were due to chance.

Question 7

Type II error

Answer 7

Null hypothesis is accepted and alt is rejected, but the alt was true -false neg
Too low struct significance evel - eg 0.01 or 1%
The ppts not acting as expected is due to chance variation hiding the causal relationship between the IV and the DV

Question 8

Distinguish between a type I and type ll error in psychological research (3 marks)

Answer 8

A Type I error occurs when a researcher wrongly rejects the null hypothesis, thinking there is an effect when there isn’t one (a false positive). A Type Il error happens when the researcher wrongly accepts the nuil hypothesis, missing an effect that actually exists (a false negative). These errors are linked to the level of significance and statistical pawer.

Question 9

What is the accepted level of significance in psychological research? (1 mark)

Answer 9

P=<0.05
Less than 5% probability that the results are due to chance

Question 10

Explain why a psychologist might prefer a lower level of significance. (2 marks)

Answer 10

A psychologist might prefer a lower level of significance (e g., 0.01) to reduce the likelihood of making a Type I error. This is important in research where false positives could have serious consequences, such as medical or forensic psychology or controversial theories

Question 11

So to reduce the chance of a type I error…. But this can lead to …

Answer 11

To reduce the chance of a Type 1 error, a researcher can decide to use a P=<0.01 level of significance, however, this then increases the likelihood of a Type 2 error.
The same is true in reverse; using P=<0.05 reduces the chance of a Type 2 error but increases the possibility of a Type 1 error compared to using P=<0.01.

Question 12

What is meant by a Type II error? Explain why psychologists normally use the 5%
level of significance in their research.

Answer 12

A Type II error would occur where a real difference in the data is overlooked as it is wrongly
accepted as being not significant, accepting the null hypothesis in error (a false negative)
The 5% level is used as it strikes a balance between the risk of making the Type I and II errors (or
similar)

Question 13

Wording when using chi 2

Answer 13

The value of chi squared is or isn’t sig at given p value
Calc/obs value is higher/lower than critical value