This study was conducted using one group of 28 college students who consumed both high- and low- aspartame diets and differences in their responses to these two diets (interventions) were examined. Lindseth et al. (2014, p. 187) stated that “the participants served as their own controls” in this study, indicating the scores from the one group are paired. In Table 2, the t-tests are identified as paired t-tests, which are conducted on dependent or paired samples.
The interventions were high-aspartame diet (25 mg/kg body weight/day) and low-aspartame diet (10 mg/kg body weight/day). The dependent or outcome variables were spatial orientation, working memory, mood (irritability), depression, and headaches (see Table 2 and narrative of results).
Differences were examined with the paired t-test (see Table 2). This statistical technique is appropriate since the study included one group and the participants served as their own control (Plichta & Kelvin, 2013). The dependent variables were measured at least at the interval level for each subject following their consumption of high- and low-aspartame diets and were then examined for differences to determine the effects of the two aspartame diets.
Means and standard deviations (SDs) were used to describe spatial orientation for high- and low-aspartame diets. The data in the study were considered at least interval level, so means and SDs are the appropriate analysis techniques for describing the study dependent variables (Grove et al., 2013).
Standard deviation (SD) is a measure of dispersion that was reported in this study. Spatial orientation following a high-aspartame diet had an SD = 4.2 and an SD = 4.3 for a low-aspartame diet. These SDs are very similar, indicating similar dispersions of spatial orientation scores following the two aspartame diets.
Paired t-test = 2.4 for spatial orientation, which is a statistically significant result since p = .03*. The single asterisk (*) directs the reader to the footnote at the bottom of the table, which identifies * p < .05. Since the study result of p = .03 is less than α = .05 set for this study, then the result is statistically significant.
There is no significant difference in spatial orientation scores for participants following consumption of a low-aspartame diet versus a high-aspartame diet. The null hypothesis was rejected because of the significant difference found for spatial orientation (see the answer to Question 6). Significant results cause the rejection of the null hypothesis and lend support to the research hypothesis that the levels of aspartame do effect spatial orientation.
The researchers reported, “Based on Vandenberg MRT scores, spatial orientation scores were significantly better for participants after their low-aspartame intake period than after their high intake period (Table 2)” (Lindseth et al., 2014, p. 190). This result is clinically important since the high-aspartame diet significantly reduced the participants’ spatial orientation. 176Healthcare providers need to be aware of this finding, since it is consistent with previous research, and encourage people to consume fewer diet drinks and foods with aspartame. The American Heart Association and the American Diabetic Association have provided a statement about the effects of aspartame that can be found on the National Guideline Clearinghouse website at http://www.guideline.gov/content.aspx?id=38431&search=effects+aspartame
There was no significant difference in reported headaches based on the level (high or low) of aspartame diet consumed. Additional research is needed to determine if this result is an accurate reflection of reality or is due to design weaknesses, sampling or data collection errors, or chance (Grove et al., 2013).
Additional studies are needed with larger samples to determine the effects of aspartame in the diet. Lindseth et al. (2014) conducted a power analysis that indicated the sample size should have been at least 30 participants. Thus, the sample size was small at N = 28, which increased the potential for a Type II error. Diets higher in aspartame (40–50 mg/kg body weight/day) should be examined for neurobehavioral effects. Longitudinal studies to examine the effects of aspartame over more than 8 days are needed. Future research needs to examine the length of washout period needed between the different levels of aspartame diets. Researchers also need to examine the measurement methods to ensure they have strong validity and reliability. Could a stronger test of working memory be used in future research?