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Open access

Ksenija Dumičić and Berislav Žmuk

Decision making based on single and double acceptance sampling plans for assessing quality of lots

Background: Acceptance sampling is a statistical tool of quality control. Sampling plans and operating characteristic (OC) curves are very useful for conducting acceptance sampling and provide the quality manager with tools to evaluate the quality of a production run or shipment. There are developed different sampling plans, but common used in practise are single and double acceptance sampling plans. Objectives: The goal of the paper is to test if applying of single and double sampling plan can lead to statistically significant different conclusion about quality level of observed lot. Methods/Approach: Statistical tests of difference in proportions are used to test if there is some statistically significant difference in probabilities of lot fraction defectives between a single and a double sampling plan at the same levels of probability of acceptance. Results: The results of the analysis show that in some cases there is statistically significant difference. Namely, the quality manager should be careful when he chooses to use, instead of the first, the second sampling plan with different parameters because on that way he could make statistically significant different conclusion about quality level of observed lot. Conclusions: The paper shows that some intentional manipulations by using different sampling plans are possible.

Open access

Berislav Žmuk

Abstract

The average expected duration of human life is rising because of different reasons. On the other hand, not only the duration, but the quality of life level is important, too. The higher the quality of life level, the citizens’ happiness and satisfaction levels are higher, which has positive impact on the development and operating of an economy. The goal of this paper is to identify groups of European countries, using statistical hierarchical cluster analysis, by using the quality of life indicators, and to recognise differences in quality of life levels. The quality of life is measured by using seven different indicators. The conducted statistical hierarchical cluster analysis is based on the Ward’s clustering method, and squared Euclidean distances. The results of conducted statistical hierarchical cluster analysis enabled recognizing of three different groups of European countries: old European Union member states, new European Union members, and non-European Union member states. The analysis has revealed that the old European Union member states seem to have in average higher quality of life level than the new European Union member states. Furthermore, the European Union member states have in average higher quality of live level than non-European Union members do. The results indicate that quality of life levels and economic development levels are connected.

Open access

Berislav Žmuk

Abstract

Background: In the cluster sampling approach many parameters have influence on lowering the survey costs and one of the most important is the intracluster homogeneity.

Objectives: The goal of the paper is to find the most optimal value of intracluster homogeneity in case when two or more questions or variables have a key role in the research.

Methods/Approach: Five key variables have been selected from a business survey conducted in Croatia and results for the two-stage cluster sampling design approach were simulated. The calculated intracluster homogeneity values were compared among all the five observed questions and survey costs and precision levels were inspected.

Results: In the new cluster sampling design, for the fixed precision level, the lowest survey costs would be achieved by using the intracluster homogeneity value which is the closest to the average intracluster homogeneity value among all the key questions. Similar results were obtained when survey costs were held fixed.

Conclusions: If there is more than one key question in the survey, then the best solution would be to use an average intracluster homogeneity value. However, one should notice that in that case minimum survey costs would not be reached, but the precision levels would increase at all key questions.

Open access

Berislav Žmuk

Abstract

Background: In order to conduct a probability business survey, a high quality sampling frame of enterprises is needed.

Objectives: The goal of the paper is to investigate publicly available online businesses lists which can be used as sampling frames in business surveys in Croatia and to find out whether they have a satisfactory quality level.

Methods/Approach: Publicly available businesses lists in Croatia are examined and their appropriateness for use in different modes of data collection as business sampling frames is inspected. The advantages and disadvantages of businesses lists are discussed and compared.

Results: Overall 11 online businesses lists are considered as business sampling frames in the paper. The comparison analysis has shown that businesses lists from the government institutions are the best choice when business surveys are conducted face-to-face, by mail and/or by telephone. However, none of the observed businesses lists is good enough to be used in a business web survey.

Conclusions: The research has shown that the publicly available online businesses lists are of a satisfactory level of quality only if traditional data collection modes are used. Unfortunately, they are not appropriate in business web surveys. Therefore, the development of a business register in Croatia is a prerequisite for conducting probability and representative business web surveys in the future.

Open access

Berislav Žmuk

Abstract

This paper aims to address differences in the use of statistical methods by enterprises as one of the factors leading to the uneven level of economic development between different regions. For research purposes, a web survey was conducted on a sample of 667 Croatian enterprises in 2013. In order to better distinguish between Croatian regions, a complex sample survey design was used. The results show that the highest rates of statistical methods use among enterprises are in the Central and East region (36.96%). The conducted logistic regression analysis showed that the enterprises that use statistical methods have 63.5% greater odds of achieving positive net income than enterprises that do not. The research results point out the need for the adoption of statistical methods as a tool for achieving higher net income and for reducing economic dissimilarities between regions.

Open access

Berislav Žmuk

Abstract

The aim of this paper is to introduce and develop additional statistical tools to support the decision-making process in stock trading. The prices of CROBEX10 index stocks on the Zagreb Stock Exchange were used in the paper. The conducted trading simulations, based on the residual-based control charts, led to an investor’s profit in 67.92% cases. In the short run, the residual-based cumulative sum (CUSUM) control chart led to the highest portfolio profits. In the long run, when average stock prices were used and 2-sigma control limits set, the residual-based exponential weighted moving average control chart had the highest portfolio profit. In all other cases in the long run, the CUSUM control chart appeared to be the best choice. The acknowledgment that the SPC methods can be successfully used in stock trading will, hopefully, increase their use in this field.

Open access

Ksenija Dumičić and Berislav Žmuk

Abstract

Background: The stock exchange, as a regulated financial market, in modern economies reflects their economic development level. The stock market indicates the mood of investors in the development of a country and is an important ingredient for growth. Objectives: This paper aims to introduce an additional statistical tool used to support the decision-making process in stock trading, and it investigate the usage of statistical process control (SPC) methods into the stock trading process. Methods/Approach: The individual (I), exponentially weighted moving average (EWMA) and cumulative sum (CUSUM) control charts were used for gaining trade signals. The open and the average prices of CROBEX10 index stocks on the Zagreb Stock Exchange were used in the analysis. The statistical control charts capabilities for stock trading in the short-run were analysed. Results: The statistical control chart analysis pointed out too many signals to buy or sell stocks. Most of them are considered as false alarms. So, the statistical control charts showed to be not so much useful in stock trading or in a portfolio analysis. Conclusions: The presence of non-normality and autocorellation has great impact on statistical control charts performances. It is assumed that if these two problems are solved, the use of statistical control charts in a portfolio analysis could be greatly improved.

Open access

Berislav Žmuk and Iris Mihajlović

Abstract

The expansion of the Internet has radically changed the way in which citizens travel, book and organise travel arrangements. Since innovation and new information technologies have become crucial determinants to encourage competitiveness in the tourism sector in Europe, this article investigates how selected development indicators influence the Percentage of individuals that use Internet for travel and accommodation services. Eurostat data for 34 European, European Union (EU-28) and selected EU candidates, countries for 2017 were analysed. It has been presented that (1) Gross Domestic Product per capita in Purchasing Power Standards; (2) Percentage of population aged 15 to 64, by tertiary education; as well as (3) Percentage of individuals aged 16 to 74, who have basic or above basic overall digital skills, all correlate positively and strongly with the main variable under study. The conducted regression analysis has shown that variable digital skills has the greatest impact on the main variable under the study. The K-mean clustering of countries resulted with four clusters. The Western Balkan countries can be found in a cluster which has in average the lowest values of all four variables in compare to the averages of other three clusters.

Open access

Ksenija Dumičić, Lea Bregar and Berislav Žmuk

Abstract

Background: There are several factors that lead to an improved level of competitiveness and increased net income of enterprises. Previous studies have shown that an appropriate use of statistical methods has positive effects on the level of competitiveness and on enterprises’ net income in general. Objectives: This study analyses the statistical methods use in Croatian small enterprises. The goal of this research is to establish whether most Croatian small enterprises use statistical methods and whether the enterprises that use statistical methods on average have greater net income than the enterprises that do not use statistical methods.

Methods/Approach: A web survey was conducted on the sample of 631 small enterprises in Croatia in 2012. In the analysis a complex survey design was taken into account. Results: The results have shown that in most Croatian small enterprises statistical methods are not used. The enterprises that use statistical methods on average have greater net income than the enterprises that do not use them.

Conclusions: The results suggest that even though the use of statistical methods in small enterprises leads to higher net income, they are not used in the majority of Croatian small enterprises. If Croatian small enterprises want to succeed on the demanding European Union’s market they should consider using statistical methods in their business.

Open access

Ksenija Dumičić, Ivana Skoko Bonić and Berislav Žmuk

Abstract

The aim of this paper is to analyse the influence of the development level indicators on the e-commerce, i.e. on the online purchase by individuals, in selected European countries in 2013. In the analysis, the main variable under study and all the independent variables are included as standardised. Based on nine variables, the principal component analysis with varimax rotation was performed and the two extracted factors were used as the regressors in the multiple regression analysis. In the regression model both components, Factor 1, which includes seven variables, called Prosperity, Investing in Education and IT Infrastructure, and Awareness, and Factor 2, comprised of two variables, called IT Skills, are statistically significant at the significance level of 1%. Both factors show a positive correlation with the online purchase of individuals. Inclusion and analysis of distributions and impacts of even nine independent variables, which make up two distinct factors affecting the e-commerce, make a new contribution of this work.