**2.3 Statistical treatment**

The following statistical tests have to be applied in order to analyze the degree of agreement between the individual data obtained for the standardization of the analytical method:

The Shapiro–Wilk and Levene tests are used to evaluate the normality and homogeneity of the data obtained for repeatability and intermediate precision, with a confidence interval greater than 95%. It is also necessary to determine the standard deviation and the coefficient of variation to determine whether the method is precise.

For linearity, the Pearson correlation coefficient and the coefficient of determination (R2) must be determined, a one-way ANOVA applied, and the t-student test performed to evaluate whether the slope differs significantly from zero.

For samples of thermoformed, flexible films, flour and starch samples, one-way ANOVA needs to be applied in order to determine whether there are any significant differences between them.

For statistical analysis, programs such as: Microsoft Office Excel 2007 and SPSS Statistical Software version 11.5 are used.
