Reliability and Validity

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Presentation transcript:

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

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

Some definitions… Validity Reliability Objectivity

Types of Experimental Validity Internal External

Validity Logical Statistical

Logical Validity

Statistical Validity

Logical/Statistical Validity

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)

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

Threats to Internal Validity

Threats to Internal/External Validity e.g. O1 T O2 PLACEBO P O3 R O4

Threats to Internal/External Validity

Threats to External Validity

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

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

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

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

Rater Reliability (Objectivity) Intrarater reliability Interrater reliability

Threats to Reliability

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…

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 week’s lecture Does not contribute to final assessment but will be marked DO NOT contact author or order articles.

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

J.Betts@bath.ac.uk