[Types of variables and distributions].

Variable presents any measurable quality of an individual or a system. Data are collected by measuring variables. There are four scales of measurement: nominal, ordinal, interval and ratio. There are qualitative and quantitative variables. Categorical variables are measured with nominal and ordinal, while numerical variables are measured with interval and ratio scale of measurement. Sample data are usually grouped around some central location value. At the same time there is always a higher or greater variability present in the sample. Measures of central tendency and variability are ways of summarizing data. Distribution characteristics are of utmost importance because they form a basis for the choice of descriptive statistics and significance tests. Normally and not-normally distributed data are tested with parametric and nonparametric tests, respectively. Equality of variance is also a criterion for the choice of significance test. Computer programs offer a full range of statistical procedures and calculations. In order to use them it is necessary to be familiar with some basics in biostatistics. This lecture is an introduction to the types of data, levels of measurement, ways of summarizing data and types of distributions.