Summary Of The External Validity Of A Study

The participants selected and the methods of selection will ultimately define the boundaries of the study results. Judging the external validity of a study (i.e.: Assessing to whom the study results may be applied) requires that a comprehensive description of the selection standards and selection methods and descriptive data regarding the study sample be provided.

This subsection could begin with a brief introduction of the study setting, in order to contextualize the work showed. This should include the setting, location(s) and relevant dates of the study, indicating, for example, periods of recruitment, exposures or interventions, follow-up and data collection. After introduction of the work setting, there are three major issues that should

In the case of experimental studies on human issues (clinical trials) the approval by a national ethical committee is legally required. If the study brings up any additional specific ethical concern this should be adequately identified (e.g.: Studies on especially vulnerable subgroups). Although not directly linked to the ethical considerations, it is important to stress that for experimental studies on human subjects (clinical trials) authors should give an appropriate reference to the registration of the study protocol on a clinical trials registration

This should include an explanation of how the disciplines were identified and how they were sampled from the target population under study (sampling methods). When selecting subjects from a target population, probabilistic sampling methods or known as random sampling or chance sampling are preferred because they more appropriately guarantee representativeness of the sample. This is because under this sampling design, every item of the universe has an equal chance of inclusion in the sample. It is so to say, a lottery method in which individual units are picked up from the whole group not deliberately but by some mechanical process. When reporting probabilistic sampling methods authors should report the sampling frame, the instruments used for the random selection process and, if appropriate, the use of complex sampling methods with stratification or clustering and weighting procedures. Although probabilistic methods are preferred, for practical reasons, non-probabilistic sampling methods (non-random samples) are much more common. Non-probability sampling is also known by different names such as deliberate sampling, purposive sampling and judgement sampling. In this type of sampling, items for the sample are selected deliberately by the researcher: his choice concerning the items remains