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 Spearman's correlation coefficient; new coefficient of association of quality features created and proven by the author's book which is equivalent to Pearson's correlation coefficient (this coefficient of association presented in the book can be tested for instance by a simple t-Student test); the possibilities of the application of the association coefficient which can be used to management decision in the enterprise; the possibilities of application of the linear probability function in the enterprise with advantages of its application; the econometric models of limited dependent variables with general formula of logit transformation and possibilities of their use in undertaking management decisions in enterprise.