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MSc Applied Psychology PYM403 Research Methods Validity and Reliability in Research.

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Presentation on theme: "MSc Applied Psychology PYM403 Research Methods Validity and Reliability in Research."— Presentation transcript:

1 MSc Applied Psychology PYM403 Research Methods Validity and Reliability in Research

2 -Aims of session are to consider  Internal / external validity  Threats to internal validity  Considerations and evaluation of external validity  Effective research design and implementation  Critiquing a journal article

3 Validity and Reliability: Indicative Reading Books on conducting Research Methods, e.g., Breakwell, G. M., Hammond, S., & Fife-Shaw, C. (1999). Research Methods in Psychology (2 nd ed). London: Sage. Internet sites, e.g., - Validity - Reliability

4 Internal / External Validity Internal Validity -Extent to which we can conclude a causal relationship between two variables External Validity - Extent to which we can generalise from sample, settings, variables manipulated, and variables measured Research as tension between Internal / External validity

5 Internal Validity - “True” experiment better able to conclude IV has effect on DV - Features of true experiment include manipulation of IVs, randomisation techniques, control of other variables - “Correlation does not imply causation” - What about other quantitative designs looking for “differences between groups/conditions” and hoping for causal explanation? - Various threats to internal validity when design not true experiment - can mean rival hypotheses - may or may not be plausible - Your job as researcher to spot them and discuss - Despite limitations, still very important to carry out studies “in the field”

6 Threats to Internal Validity (Single Group) -History – events between 1 st and 2 nd measurement -Maturation – participant changes over time per se (i.e. not events) e.g., older, more hungry, less motivated -Testing – effect of taking test once on taking the scores a second time -Instrumentation – changes in instrument or observers / scorers over time -Statistical regression – particularly when groups selected on basis of extreme scores (selection bias)

7 Threats to Internal Validity (Multiple Groups) - Selection bias – differential selection of respondents for comparison groups (self-selected groups can be problem) - Sources of bias interact e.g., Selection history threat ◦ Selection maturation threat ◦ Selection testing threat ◦ Selection instrumentation threat Selection regression threat - Mortality – differential loss of participants from groups

8 Threats to Internal Validity (Social Interaction Threats) - Diffusion of Treatment – “second hand training” - Compensatory Equalization of Treatment - Compensatory Rivalry - Demoralization Effects - Local History – difference in conditions in which groups were tested

9 External Validity - Research would ideally maximise both Int & Ext - not always possible. - In general, true experiment will maximise internal validity, probably at expense of external validity, while field study or observational research will gain in external validity, losing some internal validity. -Still very important to carry out real-life empirical research – just need to be aware of any limitations in interpretation

10 External Validity: Considerations - Sample Modelling – you first identify the population you want to generalise to and then draw a sample from that population - Proximal Similarity (Gradient of Similarity) – identify factors that are more or less similar to the original study - Threats to External Validity Unusual people Unusual places Unusual times

11 Proximal Similarity

12 External Validity: Evaluation - Population Selection - generalizability? - Operational Definitions - IVs / DVs operationally defined? - Parameter Values - Are there reference groups / norms? - Pretest - Could a pretest have influenced performance? - Demand Characteristics Hawthorne Effect - were groups made to feel special? Pygmalian Effect - Were subtle cues given?

13 Reliability -Inter-Rater or Inter-Observer Reliability Used to assess the degree to which different raters/observers give consistent estimates of the same phenomenon. -Test-Retest Reliability Used to assess the consistency of a measure over time. -Parallel-Forms Reliability Used to assess the consistency of the results of two tests constructed in the same way from the same content domain. -Internal Consistency Reliability Used to assess the consistency of results across items within a test.

14 Orienting Questions  Try to identify the design of the main study.  Is it a “true experiment” or not?  What are the variables, and are they manipulated?  What threats to validity? Do they try to address these?  What other questions addressed or other statistics used?  What are the good points? Any criticisms?

15 Critiquing Research -Purpose is critical evaluation 1. Need to read with understanding 2. Analyse content 3. Evaluate - Should be constructively critical (not simply negative) - Appreciate contributions to psychology - Consider methodology and ingenuity of design -Should be objective - Use third person, avoid personal opinions

16 Critiquing Research: Structure - Begin by summarising research (very briefly) - background, methodology, findings, conlcusions - Then critique the work - Then briefly summarise and make your conclusions

17 Critiquing Research: Considerations -Methodology Internal / External Validity - threats to these? - Appropriate design, sampling, operationalization of variables, procedure, data collection, materials, etc. Reliability - were the measures reliable? - Contributions to current psychological knowledge How does it fit history of research in this area? What does it add to practical /theoretical aspects? How important is the study in the wider world?

18 Critiquing a Journal Article -Practice paper for critiquing Rosenthal, R. & Fode, K. L. (1963). The effect of experimenter expectation on the performance of the Albino Rat. Behavioral Science, 8 (3), 183-189.

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