### Browsing by Author "Witkowski, Marek"

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Item Badanie zmienności kosztów przedsiębiorstwa handlu detalicznego w warunkach współliniowości zmiennych kosztotwórczych(Digitalizacja i deponowanie archiwalnych zeszytów RPEiS sfinansowane przez MNiSW w ramach realizacji umowy nr 541/P-DUN/2016, 1990) Witkowski, MarekShow more The article undertakes an attempt to investigate the variability of cost of a retail enterprise. The problems connected with this task are not easy to solve. They require the methods that would reduce negative consequences of strong corelations between variables explaining the variability of costs. The existence of such corelations (i.e. of co-linearity of variables) is detrimental for a correct determination of intensity and direction of influence of particular cost-creating factors on cosi It may also be responsible for mistaking an insignificant cost- -creating variable for a significant one. Nowadays, many methods of neutralizing co-linearity exist. Among them, ridge regression method is considered highly efficient. The article exemplifies application of the latter method to the cost analysis of a retail enterprise and compares its results with the results of the classic method of smallest squares by verifying the regression models of cost assessed by both methods. The advantages and disadvantages of ridge regression method in the context of classic regression method have been examined.Show more Item Metoda głównych składowych jako metoda identyfikacji czynników określających poziom kosztów przedsiębiorstw handlu detalicznego(Wydział Prawa i Administracji UAM, 1980) Witkowska, Anna; Witkowski, MarekShow more In the elaboration an attempt has been taken up to identify factors determining cost level of retail trade enterprises. At the initial stage of research choice of potential explanatory variables has been done as well as quantitative analysis of their influence on costs when classical linear regression used. It turned out, however, that many explanatory variables are then statistically insignificant. The appraisal of used regression model revealed that it could not be used as a tool of problem solution. The main reason was a strong correlation among explanatory variables, i.e. phenomenon of collinearity. An attempt to eliminate the collinearity thanks to factor analysis in form of the main factors method has been taken up in further part of the article. It has been shown that the method gives also — along with the complete elimination of collinearity at the stage of costs model estimation — a possibility of separation of the most important determinants from the starting set of potential cost-creating factors. Limitations to the utilization of the presented procedure have also been pointed out. Empirical exemplification of the presented method has been carried out ox* the ground of source material concerning costs and results of activities of retail trade enterprises of food products in Poland.Show more Item Próba wykorzystania zmiennych syntetycznych w badaniu kosztów przedsiębiorstwa handlowego(Wydział Prawa i Administracji UAM, 1983) Witkowski, MarekShow more The study is devoted to the dynamic analysis of costs in a commercial enterprise in the aspect of its causation conditioning. The article consists of three parts. The first one raises the subject of comparability of statistical information over time, as any analysis performed in the scale of an enterprise has to be dynamic. The second part is an attempt to apply the classical method of regression in the analysis of cost variation. The obtained results however, could be accepted uder reserve. These objections were caused by the fact that charging of regression parameters effected by the occurence of collinearity of cost generating variables had to be taken account of upon the assessment on cost variations based on economic time series. By reason of the above, there is a proposition of a dynamic analysis of costs presented in the closing part of the article, with an employment the method of synthetic variables (hereinafter called the MSV). The author presents a process of construction of the so called measure of activity developement in a commercial enterprise, which was introduced. Next the measure is treated as the basic factor conditioning a dynamic cost variation and it is introduced to the dynamic cost equation. The empirical MSV verification performed on the source material proved its unquestionable usefulness for the analysis of the problem.Show more Item PRZEGLĄD PIŚMIENNICTWA(Wydział Prawa i Administracji UAM, 1999) Witkowski, MarekShow more Prognozowanie gospodarcze. Metody i zastosowania, praca zbiorowa pod red. Marii Cieślak, PWN, Warszawa 1998, ss. 311.Show more Item Zjawisko współliniowości w statystycznych badaniach przyczynowo-skutkowych procesów ekonomicznych(Wydział Prawa i Administracji UAM, 1982) Witkowski, MarekShow more The elaboration is devoted to the problems of variables collinearity and its repercussions for a study process of cause-effect conditions of socio-economic phenomena. The study is carried out with the use of statistical methods of interdependence analysis. It appears that collinearity is a crucial obstacle for correct estimation of mutual relations between economic variables. The solution of that problem needs several measures. Their synthesis has been accomplished in the paper. There have been discussed the following problems: 1) measurement of collinearity (Glauber-Farrar test), 2) range of collinearity on a set of explanatory variables (F-test, t-test), 3) search for ways of reduction adverse effects of collinearity. In the second part of the paper has been presented one of the methods of reducing collinearity i.e. the ridge regression method. That method is generally founded on such basis that it is better to use biassed estimators but with variance smaller than variance of those estimators obtained with the help of the CLSM. The method has been implemented for an analysis of a real statistical date. The figures regarded costs and their determinants in state-owned foodstuffs retail trading enterprises. The study confirmed large utility of the ridge regression method in a process of identification of cost-creating factors, but considering narrow scope of its hitherto applications further verification studies are indispensable.Show more