Research methods - Inferential testing Flashcards
What is the aim of inferential statistics?
To discover if your results are statistically significant.
What does being statistically significant mean?
The result is unlikely to have occurred through chance.
What is the most common level of significance?
Psychologists use the 5% level (0.05). This means that just 1 in 20 of results could have occurred due to chance.This level is seen as a representing a balance between a type I and type II error.
How do we express our results in terms of the null hypothesis?
If a result is statistically significant, we can reject the null hypothesis. If the result is not statistically significant we must accept the null hypothesis.
What percentage of confidence do we need that the results were due to the manipulation of the IV in order to reject the null hypothesis?
95%
What is a type I error?
False positive
The alternative/ experimental hypothesis is wrongly accepted when the data is not significant
Why are type I errors often caused by?
Often caused by using a significance level that is too lenient e.g. 10%, 0.10, 1 in 10, p≤0.10. Not being cautious enough.
What is a type II error?
False negative
The alternative/experimental hypothesis is wrongly rejected when the data is actually significant.
What are type II errors often caused by?
Often caused by using a significance level that is too strict e.g. 1%, 0.01, 1 in 100, p≤0.01. Being over cautious.
How do we find out if the results are statistically significant?
It is necessary to compare the calculated value against the critical value in a critical value table to see if the result is statistically significant and if the null hypothesis can be rejected.
What is a directional hypothesis? (one-tailed)
A directional hypothesis says that the independent variable will have an effect on the dependent variable. It will state what that effect will be (in other words, the direction of results).
e.g eating cheese before bed will disrupt a person’s sleep
What is a non directional hypothesis? (two-tailed)
A non-directional hypothesis just says that the independent variable will affect the dependent variable BUT it does not predict how the IV will affect the DV.
E.g. Eating cheese before bed will affect a person’s sleep.
What is the sign test a test of?
A test of difference. It is used to compare scores in data sets from a repeated measures design. It does this by converting the score changes into nominal data (a frequency count for the number of participants in different categories - e.g 5 people passed their flute exam first time; 2 people did not pass first time)
How is the sign tested carried out?
- Look at whether the change in results is in a positive or negative direction.
- Count the number of + and - signs.
- If the hypothesis is non-directional (two-tailed) then the smaller of these two values is the calculated value (C). If the hypothesis is directional (one-tailed) then we must look at whether it is positive or negative and the calculated value is the value that is the same direction as that
- Pairs of scores with no change are omitted.
What does a calculated value have to be in order to be significant?
It has to be less than or equal to the critical value.
