R Commander: Case study 3: Comparing two independent groups and looking for outliers

Описание: Sebastian et at75 developed a low-maintenance, ease-of-use, multidimensional pH sensor with intrinsically conducting polyaniline material (PANI-pH). They determined the concentration of acetic acid using the PANI-pH sensor and the standard glass pH electrode (spreadsheet 3). It was the classic comparison between the proposed and the standard method.
The first step in the case study was to look for outlier values. Outlier results may be found using the boxplots and the Grubs test. In this case, both approaches identified trial four as an outlier. Thus, this outlier value was excluded.
In the second step, the Shapiro-Wilk test was carried out, and it showed that the concentrations obtained using the proposed method were not normally distributed, while those obtained using the standard method were normally distributed.
In the third step, methods variances (precision) and means were compared, where the F-test and the Bartlett test showed that methods variance were nonequivalent, and the Welch test showed that both methods provided equivalent results.
Since the data was not normally distributed, students could also compare the two groups using the nonparametric Wilcoxon test, which showed that both groups were equivalent.
The main learning goal of this case study was to find outliers using boxplots and compare two independent groups. Students must keep in mind that outlier results must be deleted before any comparison between groups.
Data set:
https://drive.google.com/file/d/1kkNU...