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Reliability and Validity Introduction to Study Skills & Research Methods (HL10040) Dr James Betts.

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Presentation on theme: "Reliability and Validity Introduction to Study Skills & Research Methods (HL10040) Dr James Betts."— Presentation transcript:

1 Reliability and Validity Introduction to Study Skills & Research Methods (HL10040) Dr James Betts

2 Lecture Outline: Definition of Terms Types of Validity Threats to Validity Types of Reliability Threats to Reliability Introduction to Measurement Error.

3 Some definitions… Validity Reliability Objectivity

4 Types of Experimental Validity Internal External

5 LogicalStatisticalValidity

6 Logical Validity

7 Statistical Validity

8 Logical/Statistical Validity

9 Interesting Example: Breast Cancer Incidence: ~1 % (0.8 %) (i.e. a positive result should be detected for approximately 1 in every 100 women tested ) Sensitivity: ~90 % (87 %) (the mammogram is sensitive enough that approximately 90 in every 100 breast cancer patients will receive a positive result) Specificity: ~90 % (93 %) (the mammogram is specific enough that approximately 90 in every 100 healthy patients will receive a negative result). Data from Kerlikowske et al. (1996)

10 Quick Test What is the probability that a patient receiving a positive result actually has breast cancer?

11 Threats to Internal Validity

12 e.g. O1O1 TO2O2 P O3O3 R O4O4 Threats to Internal/External Validity

13

14 Threats to External Validity

15 Reliability Subject 1 60 ml.kg -1.min -1 60 ml.kg -1.min -1 60 ml.kg -1.min -1 Subject 2 55 ml.kg -1.min -1 55 ml.kg -1.min -1 55 ml.kg -1.min -1 Subject 3 70 ml.kg -1.min -1 70 ml.kg -1.min -1 70 ml.kg -1.min -1

16 Reliability Subject 1 60 ml.kg -1.min -1 65 ml.kg -1.min -1 65 ml.kg -1.min -1 Subject 2 55 ml.kg -1.min -1 60 ml.kg -1.min -1 60 ml.kg -1.min -1 Subject 3 70 ml.kg -1.min -1 75 ml.kg -1.min -1 75 ml.kg -1.min -1

17 Reliability Subject 1 60 ml.kg -1.min -1 72 ml.kg -1.min -1 57 ml.kg -1.min -1 Subject 2 55 ml.kg -1.min -1 61 ml.kg -1.min -1 52 ml.kg -1.min -1 Subject 3 70 ml.kg -1.min -1 40 ml.kg -1.min -1 84 ml.kg -1.min -1

18 Types of Reliability Subject 1 60 ml.kg -1.min -1 63 ml.kg -1.min -1 57 ml.kg -1.min -1 Subject 2 55 ml.kg -1.min -1 56 ml.kg -1.min -1 48 ml.kg -1.min -1 Subject 3 70 ml.kg -1.min -1 65 ml.kg -1.min -1 66 ml.kg -1.min -1

19 Rater Reliability (Objectivity) Intrarater reliability Interrater reliability

20 Threats to Reliability

21 Measurement Errors Ultimately, reliability is dependent on the degree of measurement error in a given study The overall error in any measurement is comprised of both systematic and random error We will address measurement error further next week…

22 Literature Search Assignment The handout lists 8 questions which can be answered through retrieving the corresponding source articles Answer as many as possible and hand them in at next weeks lecture Does not contribute to final assessment but will be marked DO NOT contact author or order articles.

23 Selected Reading Atkinson, G. and A. M. Nevill. Statistical methods for assessing measurement error (Reliability) in variables relevant to sports medicine. Sports Medicine. 26:217-238, 1998. Holmes, T. H. Ten categories of statistical errors: a guide for research in endocrinology and metabolism. American Journal of Physiology. 286: E495-501. Thomas J. R. & Nelson J. K. (2001) Research Methods in Physical Activity, 4th edition. Champaign, Illinois: Human Kinetics

24 J.Betts@bath.ac.uk


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