intervention, preferably compared to subjects who were given placebos (see Note 6). In short, they can be randomized (clinical trial,
field trial, community trial) or nonrandomized (quasi-experimental
intervention study) (see Note 7). They can be controlled or not
controlled and, considering intervention exposure, may be classified as parallel, crossover, factorial, or community. In the crossover
design, subjects are assigned to the treatment group and, once the
interval for cessation of the residual effect of the carotenoid has
passed (wash-out period), they are transferred into the placebo
group. Under this design, each individual acts as its own control.
The factorial design is used when two or more interventions are
performed simultaneously on the same subjects.
Different aspects determine the quality of an intervention study
such as randomization (simple, block, stratified, minimized), placebo, control and double-blinding (type of masking). These contribute to obtaining a higher level of evidence in the relationship
under examination [4]. A set of criteria must be met in the case of
studies to back up nutritional/health claims for foods, that is, those
claiming that they contain significant amounts of carotenoids and
that these have certain nutritional or physiological effects [1] see
Note 8).
The randomized controlled trial is considered the most rigorous method for determining whether there is a cause–effect relationship between an intervention and outcome as it provides the
most reliable and strongest evidence in epidemiological research
[2, 4]. However, when choosing a design priority should be given
to the one which best meets the objective and gives the study the
greatest degree of validity (see Note 9).
3.2 Selection
of Subjects
Subjects should be representative of the target or reference population to which the study results are to be applied (see Note 10).
Participants must meet eligibility criteria (clearly defined inclusion
and exclusion criteria), agree to participate and sign the informed
consent form once they have been being fully informed about the
study.
Eligibility criteria should clearly describe participants so that
results can be appropriately interpreted and generalized. Criteria
typically include factors such as age, sex, nutritional status, health/
disease status, and lifestyle habits.
The number of participants should be sufficiently large to allow
valid statistical analysis and a reasonably precise measurement of
effect. Sample size must be calculated (i.e., by means of a Power and
Sample Size Program, SPSS Sample Power) for a given marker to
reflect the final outcome of the study (the number of outcomes or
endpoints is a key factor influencing the power of the study) (see
Note 11).
Intervention Studies
367
field trial, community trial) or nonrandomized (quasi-experimental
intervention study) (see Note 7). They can be controlled or not
controlled and, considering intervention exposure, may be classified as parallel, crossover, factorial, or community. In the crossover
design, subjects are assigned to the treatment group and, once the
interval for cessation of the residual effect of the carotenoid has
passed (wash-out period), they are transferred into the placebo
group. Under this design, each individual acts as its own control.
The factorial design is used when two or more interventions are
performed simultaneously on the same subjects.
Different aspects determine the quality of an intervention study
such as randomization (simple, block, stratified, minimized), placebo, control and double-blinding (type of masking). These contribute to obtaining a higher level of evidence in the relationship
under examination [4]. A set of criteria must be met in the case of
studies to back up nutritional/health claims for foods, that is, those
claiming that they contain significant amounts of carotenoids and
that these have certain nutritional or physiological effects [1] see
Note 8).
The randomized controlled trial is considered the most rigorous method for determining whether there is a cause–effect relationship between an intervention and outcome as it provides the
most reliable and strongest evidence in epidemiological research
[2, 4]. However, when choosing a design priority should be given
to the one which best meets the objective and gives the study the
greatest degree of validity (see Note 9).
3.2 Selection
of Subjects
Subjects should be representative of the target or reference population to which the study results are to be applied (see Note 10).
Participants must meet eligibility criteria (clearly defined inclusion
and exclusion criteria), agree to participate and sign the informed
consent form once they have been being fully informed about the
study.
Eligibility criteria should clearly describe participants so that
results can be appropriately interpreted and generalized. Criteria
typically include factors such as age, sex, nutritional status, health/
disease status, and lifestyle habits.
The number of participants should be sufficiently large to allow
valid statistical analysis and a reasonably precise measurement of
effect. Sample size must be calculated (i.e., by means of a Power and
Sample Size Program, SPSS Sample Power) for a given marker to
reflect the final outcome of the study (the number of outcomes or
endpoints is a key factor influencing the power of the study) (see
Note 11).
Intervention Studies
367