Saturday, August 25, 2012

African interactive atlas

Harvard University published some time ago this interactive atlas of Africa where you can compare many issues, for example, the huge ethno-diversity of the continent. Central Africa is amazingly diverse, no wonder why are there so many problems. 

Sunday, August 19, 2012

History of the world using Wikipedia

Another nice visualization, this time it is a mix of history and Wikipedia posts. Made by Gareth Lloyd and using geotagged entries on Wikipedia. This video shows history as it appears in Wikipedia. Most of the action happens in Europe and US, obviously it doesn't mean that nothing happened in other parts of the world rather that in Wikipedia, Europe and US, are more relevant than other places. Each spark has its own color which represents different fields.

He also provides his original data in Google Docs

Tuesday, August 14, 2012

European colonization was the root to present economic development

Easterly and Levine wrote a new paper about development. This time is about European settlements and its effect on economic growth. Many researchers theorise that Europeans have been a source of development and have spread economic growth worldwide (see Acemoglu, Johnson, and Robinson 2001 paper). European colonizers made other regions rich trough institutional, technological, cultural, and economical channels. Although, there seems to be an important consensus on this, no one had carried a proper empirical analysis due to lack of proper data. Easterly and Levine, “construct a new database on the European share of the population during the early stages of colonization and examine its impact on the level of economic development today.” Their results agree with the consensus: “We find a remarkably strong impact of colonial European settlement on development” They specifically argue for European effect and not only British or Protestantism. These arguments may sound Euro centrist but data is clear about it: “According to one illustrative exercise, 47 percent of average global development levels today are attributable to Europeans”. “The regressions suggest that Europeans brought factors of production that boosted long-run economic development, especially among colonies with a only a few Europeans.[…] A marginal increase in European settlement in a geographic area during colonization had an especially positive effect on the level of economic development today within that geographic region.”

I feel there is something missed in all these studies. They always use present times as point of reference. However, Europe hasn’t been always the apex of the world power. During Middle Ages the Arab world was the most powerful and technological advanced society. China was the world superpower during centuries. Ancient Egypt (Africa) was also the centre of the world before Christ. Is it true, however, that the economic expansion that Europe brought to the world is by far larger than this other civilizations, but is also true that Europe wasn’t born in the vacuum, it owes everything to China, Egypt, Babylonia, Mesopotamia,….

Sunday, August 5, 2012

Olympics and GDP

The Olympics are under way in London and everyone is expecting great results for their country. There are also many newspapers publishing charts about the medals tally and its relation to each country’s population (see The Economist, for example). Although Olympic winners seems pretty random and difficult to predict, there are people who have been able generate interesting models to estimate country’s total medals. The best analysis I could find out was made by Xun Bian a student of Illinois University in 2005. Results are shown in the following table.

Population effect is positive and significant as it is GDPpc and a Dummy for the host country. What is not so evident is the effect of civil and political liberties. Two reasons may explain that. First, clearly civil and political variables are affecting GDPpc so part of their explanatory power is inside GDPpc variable. Secondly, is interesting that the fact that communist countries like USSR (back in the 80’s) or Cuba had more medals than freer countries. This is due to the fact that communist countries had a huge central Government capable of good sports achievements and willing to take political and ideological profit from their results. However, most Not-free countries were too poor to maintain any competitive sport infrastructure. Graphically, the relation between medals and GDP is not evident as it is for GDP and number of competitors. Below I show this second relation only for Beijing’08.

Wednesday, August 1, 2012

t-student or ANOVA

I just want to remember myself that t-student compares two independent samples, so if we want to probe that averages from several samples are all equal, t-student must be carried out several times and that would change the critical value and the alpha value.

Say there are 4 (i =1,2,3 and 4) samples and their averages are µi. Our null hypothesis would be:

H0: µ1 = µ2 = µ3 = µ4

H1: averages are not all equal

t-student here would imply 6 comparisons (µ1 = µ2, µ1 = µ3, µ1 = µ4, µ2 = µ3,…) bringing a final alpha of 0.26 instead of the common 0.05

ANOVA analysis can do this. Three requirements are needed though:

Independence: k sample are independent,
Normality: all samples are distributed N(µi , σ2 i)
Homocedasticidad: all variance equal to σ2

If the F-value is less than the critical value (associated to alpha=0.05) and therefore P-value less than 0.05, then we reject the H0 (or better: we can not accept the H0).