Inferential Stats, Discussions and Abstracts!! BATs Identify which inferential test to use for your experiment Use the inferential test to decide if your hypothesis can be accepted or rejected Write a discussion based on your statistics and relate to background research Write an Abstract for your piece of research

Inferential Statistics Allow psychologists to make inferences about the findings of a piece of research when only testing a sample of the world’s population. Permit psychologists to work out, for a given probability, whether a pattern in their data has arisen by CHANCE or because there was a real difference/correlation – i.e. the pattern is SIGNIFICANT.

Inferential Statistics In order to use an Inferential test you need A null hypothesis An alternative hypothesis

Inferential Statistics What do we mean by chance? Psychologists decide on a probability that they will ‘risk’. They state how certain they are that the findings were not due to chance. Psychologists use a PROBABILITY of p < (or equal to) 0.05 There is a 5% possibility that the results occurred by chance The level of significance P can vary e.g.1% for drug trials

Type 1 and Type 2 Errors A 5% significance level is used because.. The degree of uncertainty is not a life or death matter (medical research uses 1%) If the level of significance is too high (lenient) e.g. 10% you may reject a null hypothesis that is actually true. TYPE 1 ERROR If level of significance too low (stringent) e.g 1% you may accept the null hypothesis when it is not true. TYPE 2 ERROR

Levels of Measurement Before deciding which test to use you need to identify the LEVEL of MEASUREMENT used. NOMINAL – data in separate categories e.g. red, blue and green ORDINAL – data ordered e,g putting people in order of height. The ‘difference’ between each item is not the same INTERVAL – Data using units of equal intervals e.g. counting number of correct answers RATIO – There is a true zero point e.g. time taken, distance travelled e.t.c

Observed and Critical Values TEST STATISTIC – single number produced after doing particular set of calculations depending on test used e.g rho (Spearman’ correlation test) and U (Mann- Whitney) OBSERVED VALUE – Value of the test statistic CRITICAL VALUE – value the test stat must reach in order for the null hypothesis to be rejected (these are looked up in a special table for that test) Some tests are significant if the observed value is equal to or exceeds the critical value e.g. Spearman’s and Chi-square. For Mann-Whitney and Wilcoxon to be significant the observed value should be less than the critical value

Observed and Critical Values To find the appropriate Critical Value in a table you need to know … Degrees of freedom (df) – relates to the number of ppts in the study (N). Independent groups have 2 values of N – N 1 and N 2. In Chi Square the df relates to the number of cells used. One-tailed or two-tailed test – directional hypothesis = one tailed, non-directional = two tailed Significance level – p < (or equal to) 0.05

Which Inferential Statistic? Use the text book p to help you decide which Inferential test is most appropriate for your research Note down what test you will use and why! Now try the test out on your data Was your data significant? Can you accept or reject your Hypothesis?

Writing a Discussion Write a discussion of your findings. Include the following … What did you find out? – specifically mention your descriptive stats – do they match your hypothesis, were they significant – mention the Inferential test stats Do your findings match the original research? Limitations? Suggested Modifications? Implications of research on society/psychology? What could you do next to develop this research? Look at an example -p of old Complete Companion A2

Abstract This is basically a summary at the start of a report to ‘whet the reader’s appetite’!! No more than 250 words long, it should concisely summarise the… 1.Aim - The aim was to investigate…… 2.Background -Your hypothesis (null and alternative). 3.Design - Independent/Repeated Measures. Variables. 4.Sample - Selection? Girls? Boys. 5.Results and statistical conclusions of your study- Inferential & Descriptive..Main findings. It should be written in the 3 rd person and past tense, in other words you should not write ‘I found….’ instead ‘The experiment was carried out …

Mock next week – Thursday!! Revise all you have done on Addictive Behaviour and Research Methods