Significance testing

Question 1

Significance

Answer 1

-The difference/association between two sets of data is greater than what would occur by chance, i.e. it is a meaningful result
-To find out if the difference/association is significant we need to use a statistical test

Question 2

Probability

Answer 2

-Probability is about likelihood- how likely it is that a certain event will happen if the null hypothesis were true. The accepted level of probability in psychology is 0.05 (5%). This is the level at which a researcher decides to accept or reject the null hypothesis. (More stringent 1% significance level may be used e.g. testing drug effects).
-Even though psychologists may find statistically significant differences/relationships within data, they can never find statistical certainties. This is why psychologists use phrases such as ‘this suggests’, rather than ‘this proves’.

Question 3

Calculated And Critical Values

Answer 3

-The researcher uses a statistical test to produce a calculated value
-The calculated value is compared with a critical value to decide whether the result is significant or not.
-The critical values for a particular test are given in a table of critical values

Question 4

Finding The Critical Value

Answer 4

To find the critical value, we need to know
1. The significance level (usually 0.05 or 5%)
2. The number of participants in the investigation (the N value) or the degrees of freedom (df).
3. Whether the hypothesis is directional (one-tailed test) or non-directional (two-tailed test)

Question 5

Conditions Of The Sign Test

Answer 5

-Used to analyse the difference in scores between related items, e.g the same participant is tested twice (repeated measures)
-Can be used with nominal data

Question 6

Calculations

Answer 6

1. The score for condition B is subtracted from condition A to produce the sign of difference (either a plus or a minus)
2. Add up the numbers of pluses and the number of minuses
3. Participants who achieved the same score in condition A and condition B should be disregarded, and deducted from the N value
4. The S value is the total of the less frequent sign

Question 7

Critical value

Answer 7

If S is equal to or less than the critical value, then S is significant and the null hypothesis is rejected and the alternative hypothesis accepted at the 5% level of certainty.