The sample size necessary to estimate the comparison of two means depends on the confidence level of the estimate, the power of the study, the variability of the measured variable and the magnitude of the difference that is to be detected.
Mann-Whitney U test, also called Wilcoxon rank-sum test, is a non-parametric test that allows comparing the medians of a quantitative variable for the two categories of a dichotomous qualitative variable. It is applied when the assumptions necessary to use the Student's t-test cannot be fulfilled.
Discrete probability distributions allow us to establish the full possible range of values of an event when it is described with a discrete random variable. Examples of the use of the Bernoulli, binomial, geometric, and hypergeometric distributions are shown.
Skewness and kurtosis are two of the first four moments of a normal distribution. Both can be used to test the assumption of normality of a data distribution, although they are less widely used than other contrast pr graphical methods.
The geometric mean is used when the values of the data distribution change multiplicatively, and not additively. This makes it ideal for averaging geometric progression data, such as ratios, compound interest in economics, or bacterial growths in microbiology.