statistical testing - the sign test

Question 1

what is statistical testing?

Answer 1

• it provides a way of determining whether hypothesis should be accepted or rejected.
• by using a statistical test we can find out whether differences or relationships between variables are significant (meaningful) or are likely to have occurred by chance

Question 2

explain the concept of significance

Answer 2

• just because someone found a difference is mean for example doesn’t mean it is a significant difference therefore we need to use statistical testing to find this out as it may have occurred just by chance

Question 3

explain what the sign test is

Answer 3

• A statistical test used to analyse the difference in scores between related items (e.g. the same participant tested twice)
• data should be nominal or better

Question 4

how do you carry out the sign test?

Answer 4

1. We need to be looking for a DIFFERENCE rather than an association
2. We need to have used a repeated measures design
3. We need data that is organised into categories, known as nominal data

Question 5

explain the concept of probability

Answer 5

• it occurs to the likelihood that something will happen
• what we want to know is ‘how likely are these findings if the null hypothesis is true?’
• the null hypothesis states there is no difference/association in the population. If we find a difference/association in our sample, can we say that this is ‘true’ for the population (i.e. accept the alternative hypothesis)
• the accepted level of probability (level of significance) in psychology is 0.05 (5%). This is the level at which a researcher decides that the findings are significant (meaningful) and will reject the null hypothesis

Question 6

explain what the critical value is

Answer 6

• when the statistical test has been calculated, the researcher is left with a number - the calculated value
• this needs to be compared with a critical value to decide whether the result is significant or not
• the critical values for a sign test are given in a table of critical values

Question 7

what information do you need to follow to use the critical value table?

Answer 7

• the significance level (generally 0.05/5%)
• the number of participants in the investigation (the N value or sometimes degrees of significance, df)
• whether the hypothesis is directional (one-tailed) or non directional (two tailes)

these pieces of information will allow you to locate the critical value for your data. For the sign test, the calculated value has to be equal to or lower than the critical value for the results to be significant