Proceedings

distribution of each indicator to identify whether the extreme values reach the
aggregations of some indicators. Consequently, outliers were removed using a
statistical technique called winsorization which selected 95% of the distribution for
the analysis, and, by using a simple arithmetic transformation, EPI 2008 was
determined for 149 countries and the observed values were placed on a scale from 0 to
100. EPI is a work in progress, and thus EPI 2010 was also determined. Given the fact
that the GDP values per capita for 2010 have not been made public yet, the
econometric model was developed by using the indicators calculated for 2008.
4.2. Econometric Model
Research focused on a comparative analysis using a statistical-econometric
methodology used by a wide range of authors of specialized literature. The statistical
parameters – measuring the symmetry, the normality of distribution and the
correlation between various statistical data, - are obtained by the regression function.
Data processing for the analyzed indicators was performed with the help of EViews 7
application. The quantitative data allowed the drawing up of a simple regression
model showing the dependence between the EPI indicator and the analysis factor,
GDP per capita.
The linear regression model is as follows:
yi = b + a ⋅ xi
+ ε i , i = 1,...,
n
where:
y i represents the EPI SCORE, calculated for the year 2008
x i represents GDP per capita, calculated for the year 2008
n represents the number of countries taken into account for the analysis
We will consider next the GDP per capita influences the EPI indicator for a number of
146 countries, alphabetically grouped.
The necessary series of data, necessary to estimate the values of the model, are crosssectional
data (collected for a set of statistical units):
Index EPI (2008) – marked as EPI / Source: Environmental Performance Index
2008- www.yale.edu.epi
GDP per capita (current U.S. $) (2008) - marked as GDPC / Source: World
Bank and OECD national accounts on National Accounts data files
http://data.worldbank.org/index/NY.GDP.PCAP.CD
Units of measurement and transformations on data series:
The EPI: values between 0 and 100 (100 - the country with the highest score EPI)
GDP per capita: GDP per capita is gross domestic product divided by midyear
population. GDP is the sum of gross value added by all resident producers in the
economy plus any product taxes and minus any subsidies not included in the value of
the products. It is calculated without making deductions for depreciation of fabricated
assets or for depletion and degradation of natural resources. Data are in thousand
current U.S. dollars for comparability.
We study, in a comparative manner, the data series related to this model. In this case,
the series of the EPI indicator has a Mean of 71.87, the values ranging from a
~ 1080 ~