3 Methods
The aim/hypothesis or research question is the first step in a human
intervention study and must be clearly identified since it will determine the design, development and interpretation of the results of
the study. The aim of the study should be clearly defined, preferably
using measurable terms and specifying the study’s main variables
(at least one dependent and one independent variable). Regarding
carotenoids, basically the endpoints must be relevant in the context
of vitamin A nutritional status (preventing deficiency) or in that of
prevalent chronic diseases or health conditions in which carotenoids dietary intervention would make possible to reduce risk or
improve quality of life.
Intervention studies should help produce high-quality information to improve the existing body of knowledge in the field in
question (i.e., public health and the taking of health-related decisions). Thus, the first step is to search for the latest information, for
example, in PubMed and Cochrane, in order to properly define the
objectives and design the study (see Note 5).
The important points to be considered in the design and
implementation of intervention studies on humans are those
related with the research question, subject identification, description of the intervention/exposure factors or procedures, outcome
definition, reliable markers and appropriate statistical analysis for
the study design and type of outcome indicators [17]. In this
regard, there are guidelines and checklists of the key elements that
should be included in the design, implementation and reporting/
interpretation of human intervention studies. These are useful
when setting out an intervention study to assess the effect of
foods on health/disease (i.e., [17–20].) and specifically for randomized trials, for example, in CONSORT [21] and for nonrandomized studies (e.g., [22]).
3.1 Types of Design
Study design refers to the set of strategies established to achieve the
objectives and is affected by the technical and human resources
available and by what is ethically feasible in each type of study.
The study design includes the description of the intervention and
procedures (e.g., protocol, amount of carotenoid supplied, duration of the intervention, handling of drop-outs, and type of
masking).
There are different types of design depending on the criteria
employed in the classification (e.g., its aim: analytical or descriptive;
control of how group assignments are made: observational or
experimental). Intervention studies are experimental studies in
which subjects are assigned to one of the groups and are then
monitored for a period of time (defined on the basis of the aims
and the biomarker used) to assess the effectiveness of the
366
Begon ˜ a Olmedilla-Alonso
The aim/hypothesis or research question is the first step in a human
intervention study and must be clearly identified since it will determine the design, development and interpretation of the results of
the study. The aim of the study should be clearly defined, preferably
using measurable terms and specifying the study’s main variables
(at least one dependent and one independent variable). Regarding
carotenoids, basically the endpoints must be relevant in the context
of vitamin A nutritional status (preventing deficiency) or in that of
prevalent chronic diseases or health conditions in which carotenoids dietary intervention would make possible to reduce risk or
improve quality of life.
Intervention studies should help produce high-quality information to improve the existing body of knowledge in the field in
question (i.e., public health and the taking of health-related decisions). Thus, the first step is to search for the latest information, for
example, in PubMed and Cochrane, in order to properly define the
objectives and design the study (see Note 5).
The important points to be considered in the design and
implementation of intervention studies on humans are those
related with the research question, subject identification, description of the intervention/exposure factors or procedures, outcome
definition, reliable markers and appropriate statistical analysis for
the study design and type of outcome indicators [17]. In this
regard, there are guidelines and checklists of the key elements that
should be included in the design, implementation and reporting/
interpretation of human intervention studies. These are useful
when setting out an intervention study to assess the effect of
foods on health/disease (i.e., [17–20].) and specifically for randomized trials, for example, in CONSORT [21] and for nonrandomized studies (e.g., [22]).
3.1 Types of Design
Study design refers to the set of strategies established to achieve the
objectives and is affected by the technical and human resources
available and by what is ethically feasible in each type of study.
The study design includes the description of the intervention and
procedures (e.g., protocol, amount of carotenoid supplied, duration of the intervention, handling of drop-outs, and type of
masking).
There are different types of design depending on the criteria
employed in the classification (e.g., its aim: analytical or descriptive;
control of how group assignments are made: observational or
experimental). Intervention studies are experimental studies in
which subjects are assigned to one of the groups and are then
monitored for a period of time (defined on the basis of the aims
and the biomarker used) to assess the effectiveness of the
366
Begon ˜ a Olmedilla-Alonso