The purpose of this book is to present research methods, suitable for qualitative phenomena, with the examples of their applications. This book presents: simple methods of measurement of the quality features based on the weak Stevens scales; common errors in the application of the statistical methods for the analysis of the results of the measurement in ordinal scale which were not presented in any book before; indicates the risk of application of the well-known Spearmans correlation coefficient; new coefficient of association of quality features created and proven by the authors book which...