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Validity and Reproducibility of Exposure Measurements: The Method of Triads

Validity and Reproducibility of Exposure Measurements: The Method of Triads. Edmond K. Kabagambe and Hannia Campos Harvard School of Public Health. Suggested reading. Kaaks, RJ. (1997). Am J Clin Nutr 65:1232S-1239S Ocke and Kaaks (1997). Am J Clin Nutr 65:1240S-1245S

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Validity and Reproducibility of Exposure Measurements: The Method of Triads

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  1. Validity and Reproducibility of Exposure Measurements: The Method of Triads Edmond K. Kabagambe and Hannia Campos Harvard School of Public Health

  2. Suggested reading • Kaaks, RJ. (1997). Am J Clin Nutr 65:1232S-1239S • Ocke and Kaaks (1997). Am J Clin Nutr 65:1240S-1245S • Kabagambe et al (2001). Am J Epidemiol 154:1126-1135

  3. Objectives • Define the method of triads (MOT) • Describe the MOT and interpretation of the resulting validity coefficients • Give an example to illustrate the application of the MOT

  4. Exposure in Epidemiology • Exposure can be • Discrete e.g. Yes or No • Continuous e.g. plasma cholesterol, lycopene intake • Measurement error is common with continuous exposures

  5. An example for illustration • A researcher wants to measure dietary intake of lycopene • Three methods are available • Food-frequency questionnaire • 24-hr dietary recalls/records (DR) • Biomarker (plasma concentrations)

  6. We obtain 3 observed and 1 latent exposure parameters • FFQ estimate (Q) • Average of dietary recalls (R) • Biomarker measurement (M) • True, but unknown, exposure i.e. lycopene intake (T)

  7. Q rQR rQM T R M rRM Relation between true exposure (T) and 3 surrogate measures (Q, R, and M)

  8. Validity coefficients (1) • How are they computed? • What do they measure?

  9. Validity coefficients (2) • How are they interpreted for validity or reproducibility? • Can they have confidence intervals?

  10. Example on the validation of lycopene intake • Step 1: Compute correlations • Step 2: Compute VCs • Step 3: Compare VC • Step 4: Compute 95% confidence limits

  11. Example on the validation of lycopene intake continued • Step 1: Compute correlations • Step 2: Compute VCs • Step 3: Compare VC • Step 4: Compute 95% confidence limits

  12. Conclusion • The method of triads is a simple technique for assessing validity and reproducibility of continuous exposure measurements. • Although described for nutritional epidemiological studies, this method could also be applied to other continuous exposures.

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