Quantitative research – Design, sample setting, extraneous variables

The researchers used a quasi-experimental, cross sectional study design. A quasi-experimental study design involves the use of multiple measures (in this case BMI, BF %, and high sensitive serum CRP concentration), but does not involve random assignment between a test and control group as is the case for an experimental design (Trochim, 2006). A cross-sectional study design is conducted at one point in time without follow-up measures over a prolonged time frame as happens in longitudinal studies (Tochim, 2006). The study design was appropriate since ethical reasons may not have allowed researchers to control the experimental conditions for an experimental design and a cross-sectional design was appropriate since the purpose of the study did not necessitate a follow-up inquiry.

Threats to internal validity include instrumental errors and the use of a standard (BF % of 25) with limited research support. Instrumental errors for instance may lead to erroneous BMI values and the use of BF %   is limited to the accuracy of the 25 measure as indicative of obesity. Threats to external validity include the use of a non-random sample and selection of only males of predominantly white race to carry out the study. Such threats limit the extent to which the study’s findings can be generalized to other populations (Houser, 2008).

Sample and Setting

The sample size employed  (73 %) was adequate for the current study, for instance as evaluated by Cochran’s sample size formula (illustrated in Bartlett, Kotrlik & Higgins, 2001). However, since the sample was not random, e.g. only male officers were considered, generalization of results to excluded population is not possible. The setting was also appropriate since data was collected within the occupational setting for which the study sought to assess its purposes.

Identification and Control of Extraneous Variables

The confounding variables in the current study include instrumental errors that could lead to inaccuracy in measurements. Such were controlled for by appropriate calibrations before measurement, comparison with standard weights and taking tests in duplicates to identify any discrepancy. Such measures are appropriate since they help identify when the result obtained may be an aspect of the instrumental error rather than the lack of validity of the scale under consideration. Go to part 4 here.

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