From: tomihan	Date: November 18th, 2009 07:34 am (UTC)		(Link)

Corruption Perceptions Index 2009
Short methodological note
1. The 2009 Corruption Perceptions Index (CPI) gathers data from sources that
cover the past two years. For the 2009 CPI, this includes surveys from 2008
and 2009.
2. The 2009 CPI is calculated using data from 13 sources from 10 independent
institutions. All sources measure the overall extent of corruption (frequency
and/or size of bribes) in the public and political sectors, and all sources
provide a ranking of countries, i.e., include an assessment of multiple
countries.
3. For CPI sources that are surveys, and where multiple years of the same
survey are available, data for the past two years is included to provide a
smoothing effect.
4. For sources that are scores provided by experts (risk agencies/country
analysts), only the most recent iteration of the assessment is included, as
these scores are generally peer reviewed and change very little from year to
year.
5. Evaluation of the extent of corruption in countries/territories is done by two
groups: country experts, both residents and non-residents, and business
leaders. In the 2009 CPI, the following seven sources provided data based on
expert analysis: African Development Bank, Asian Development Bank,
Bertelsmann Foundation, Economist Intelligence Unit, Freedom House,
Global Insight and the World Bank. Three sources for the 2009 CPI reflect the
evaluations by resident business leaders of their own country, IMD, Political
and Economic Risk Consultancy, and the World Economic Forum.
6. To determine the mean value for a country, standardisation is carried out via
a matching percentiles technique. This uses the ranks of countries reported
by each individual source. This method is useful for combining sources that
have a different distribution. While there is some information loss in this
technique, it allows all reported scores to remain within the bounds of the CPI,
i.e., to remain between 0 and 10.
7. A beta-transformation is then performed on scores. This increases the
standard deviation among all countries included in the CPI and avoids the
process by which the matching percentiles technique results in a smaller
standard deviation from year to year.
8. All of the standardised values for a country are then averaged, to determine a
country's score.
9. The CPI score and rank are accompanied by the number of sources, high-low
range, standard deviation and confidence range for each country.
10. The confidence range is determined by a bootstrap (non-parametric)
methodology, which allows inferences to be drawn on the underlying
precision of the results. A 90 per cent confidence range is then established,
where there is a five per cent probability that the value is below and a five per
cent probability that the value is above this confidence range.
For a detailed explanation of the CPI method please visit www.transparency.org/cpi
© 2009 Transparency International. All rights reserved.