Market shares and brand loyalty
Sometimes measurements of substances in food are available at a more detailed food coding level than consumption data. For example, measurements may have been made for specific brands of a food whereas the consumption survey did not record the brand. MCRA allows to specify market share data for subtypes of a food (e.g. A$1, A$2, A$3 are three brands of food A), and to calculate acute exposure based on such market shares.
For chronic assessments brand loyalty should be specified according to a simple Dirichlet model (Goodhardt et al. (1984)). Technically, the Dirichlet model for brand choice needs nbrand parameters
where
By definition, the market shares
Simulate consumptions for a large number
of individuals.Simulate
selection probabilities from the Dirichlet distributionFor each individual, simulate
brand choices from a multinomial distribution using the individual specific selection probabilities from step 2.For all individuals and days simulate values from the appropriate concentration distribution.
Multiply consumption with concentration to obtain exposure.