SPADE consists of several modelling options, depending on the sources of the dietary components.
The modelling features are described in more detail:
The 1-part model is intended to estimate the habitual intake
distribution of food components, foods or food groups that are
consumed daily by (almost) all subjects. This means that in the
study population (almost) all subjects have a non-zero intake on
two observed days.
The SPADE 1-part model consists of the following steps:
Figure 1: This model requires intake information measured on at least two days (e.g. 24 hr recalls)
The 2-part model is appropriate to estimate the habitual intake distribution of food components, foods or food groups that are consumed episodically. The observations can typically be divided into three groups: subjects with positive intakes on both days, subjects with only one positive intake and subjects with zero intakes on both days. If no further information is available, e.g. from a food frequency questionnaire, all subjects are assumed to be potential consumers. If information is available on the never-consumers in the survey, SPADE can take this information into account.
The SPADE 2-part model consists of the following steps:
This model requires intake information measured on at least two days (e.g. 24 hr recalls)
Figure 2: The synthetic folic acid intake from dietary supplements is spiked.
In some cases the distribution of observed intake may be spiked, for example in cases of supplements. Therefore, an alternative 2-part model is needed.
This model consists of the following steps:
This model requires information on intake from dietary supplement measured on at least two days (e.g. 24 hr recalls) and eventually information on use of supplements
The 3-part model estimates the habitual intake from foods and dietary supplements. This model is based on the first shrink then add approach. It consists of the following steps:
Figure 3: 3-part model
This model requires information on the intake of foods and dietary supplements measured on at least 2 number of days (e.g. 24 hr recalls) and information that identifies is a participant is an ever or never-user of dietary supplements.
The first shrink then add approach may also be required to estimate the habitual intake distribution from several food sources. An example is the estimation of habitual intake of a specific compound present in (high levels) in a few specific episodically conumed foods (e.g. food fortification or contaminants). For all different sources (supplements, one or more food sources or one food source with known never-users), the habitual intake distributions are estimated separately using the appropriate models. For practical reasons, in the multi-part model the habitual intake of the sources other than dietary supplements is not estimated separately for supplement users and non-users. The habitual total intake distribution is obtained by Monte Carlo sampling pseudo persons for each subject in the survey.
Figure 4: Multi-part model with first shrink than add approach
This model requires intake information on foods and supplements measured on at least two days (e.g. 24 hr recalls) and additional FFQ information on the episodically eaten foods.