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Lecture 2: Types of measurement

Lecture 2: Types of measurement. Purposes of measurement Types and sources of data Reliability and validity Levels of measurement Types of scale. Introduction. Overview of measurement section of course lecture 2: introduction lectures 3-4: screening and diagnostic tests

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Lecture 2: Types of measurement

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  1. Lecture 2:Types of measurement • Purposes of measurement • Types and sources of data • Reliability and validity • Levels of measurement • Types of scale

  2. Introduction • Overview of measurement section of course • lecture 2: introduction • lectures 3-4: screening and diagnostic tests • lectures 5-6: scales • Traditions of measurement: • “Clinimetric”: clinical, epidemiological (focus on screening and diagnostic tests) • “Psychometric”: psychology (focus on scales)

  3. Introduction (cont) • Readings: • Streiner & Norman • Gordis • other

  4. Purposes of measurement • Clinical • screening, diagnosis, monitoring in individuals • Surveillance • planning and monitoring public health and health care in populations • Research • measurement of study variables (determinants, outcomes, confounders/modifiers)

  5. Sources of data • Primary vs secondary • Clinical observations • Questionnaires and interviews • Reportable diseases and registries • Health records • Administrative databases (hospital discharges, claims, medication prescription) • Vital statistics

  6. Requirements by purpose of measurement • Clinical • discrimination between health and disease relevant to management • Surveillance • valid measurement of trends • Research • maximize validity of study results

  7. Selection of measures • Appropriateness to purpose • Feasibility • Acceptability • Cost • Validity • Reliability

  8. Validity of measurements • Synonym: accuracy • Does it measure what it is intended to? • Many types: • face, content • “eyeball” test • investigator, expert judgment • criterion (lecture 3) • construct (lecture 6)

  9. Reliability of measurements • Synonyms: reproducibility, precision, consistency • Sources of variability? • Random error vs systematic error (bias)

  10. Types of reliability: rater • Between- and within-rater/observer (inter- and intra-rater observer variation) • At single point in time • Independent ratings • May be random or systematic • Examples: • blood pressure • pathology slides

  11. Reliability: stability over time • Stability over time/ test-retest (T1 and T2 • Same conditions and rater at T1 and T2. Why? • Random or systematic • Example of systematic error: • Regression toward the mean: when subjects initially have extreme values (more likely to be in error than typical values) E.g., population blood pressure screening • Questions about undesirable beahviour • Uncalibrated instruments

  12. Example • Measurement of patient depression using clinical rating scale • Sources of variability? • Measurement of inter-rater reliability? • Results for 10 patients: • Rater 1: 3 patients are depressed • Rater 2: 5 patients are depressed • Conclusion?

  13. Types of variables (level of measurement) • Continuous (syn. dimensional, quantitative) • interval • ratio • Categorical (discrete) • dichotomous, binary • polychotomous • nominal • ordinal

  14. Response scales • Categorical or continuous? • Continuous variables can be categorized • Categorical (ordinal) variables can be analyzed as continuous (pseudocontinuous) • Example of scales • Visual analogue scale • Likert scale (agree/disgree) • Semantic differential scale

  15. Examples of measures to be used in a study: for discussion • Sources of data? Level of measurement? Type of response scale? • Use of health services during past year (doctor visits, hospitalization) • Satisfaction with medical care • Use of alcohol and drugs (current and lifetime)

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