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Wednesday, May 19, 2010


Regarding using the same participants for multiple experiments:

This may actually be NOT a "limitation" in a study of this type, but instead may be a STRENGTH of the design, depending on how this "sampling technique" was used. If all participants in the experiment were used at each of the various levels of alcohol/oxygen-enrichment, this kind of design would be a "subjects as their own control" type of design.

Especially in research involving functions such as alcohol metabolism, blood levels of chemicals such as alcohol that are administered by the "standard" route (i.e. "drinks"), etc., it may actually be an advantage to do multiple physiological measurements (at different levels of the independent variable, in this case oxygen content of beverage) on the same set of individuals, generating data that are pooled/averaged for each level of the variable of interest.

It is accepted that there is a wide range of individual differences in alcohol metabolism, influenced by individual characteristics (e.g. gender, body mass, muscle-fat ratio, genetics, etc.) that are NOT variables of interest in the study. Holding constant the "metabolic machines" (humans) used to process the alcohol at each level actually CUTS DOWN on the amount of "noise" in the data that might have been introduced by factors OTHER than the one(s) of interest. Had DIFFERENT people been used for each condition, there would be a greater amount of "participant-specific" variation in the data, that would have been much more difficult (or impossible) to account for. The degree to which alcohol metabolism was influenced NOT by oxygen-enrichment but by some individual difference(s) in metabolic processes could actually have made the investigators' results LESS EASILY ACCEPTABLE. At least with the design that was (wisely) employed, such unwanted person-related influences were reduced. The same metabolic "machines" contributed their variability equally across conditions, therefore giving more confidence that differences were the result of the variables of INTEREST, rather than some unknown, idiosyncratic, participant-related influences.

This is just one of a number of instances in which caution is advised, when critiquing an experimental design without sufficient expertise in the area.

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