Validity and Reproducibility Validity and Reproducibility of Exposure Measurements: of Exposure Measurements: The Method of TriadsThe Method of Triads

Edmond K. Kabagambe and

Hannia Campos

Harvard School of Public Health

Suggested readingSuggested 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

ObjectivesObjectives

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

Exposure in EpidemiologyExposure 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

An example for illustrationAn 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)

We obtain 3 observed and 1 We obtain 3 observed and 1 latent exposure parameterslatent exposure parameters

FFQ estimate (Q)Average of dietary recalls (R)Biomarker measurement (M)True, but unknown, exposure

i.e. lycopene intake (T)

Relation between true Relation between true exposure (T) and 3 surrogate exposure (T) and 3 surrogate measures (Q, R, and M)measures (Q, R, and M)

T

Q

MR

rQMrQR

rRM

Validity coefficients (1)Validity coefficients (1)

How are they computed?

What do they measure?

Validity coefficients (2)Validity coefficients (2)How are they

interpreted for validity or reproducibility?

Can they have confidence intervals?

Example on the validation of Example on the validation of lycopene intakelycopene intake

Step 1: Compute correlationsStep 2: Compute VCsStep 3: Compare VCStep 4: Compute 95%

confidence limits

Example on the validation of Example on the validation of lycopene intake continuedlycopene intake continued

Step 1: Compute correlationsStep 2: Compute VCsStep 3: Compare VCStep 4: Compute 95%

confidence limits

ConclusionConclusion

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.