Wednesday, April 29, 2015

Biographical note: On the Road

The Blog has been less active than usual because I'm on the road these days. I was at the AAG Conference in Chicago last week and I'm in Berkeley this week*. The level of activity will remain lower than usual next week, when I'll be in Greece for a workshop on Transportation Equity.

* By the way, this is the view from 'my office' today at Berkeley library.

[Rafael Pereira, me]

Fatalities from car accidents per billion kilometers

Thursday, April 16, 2015

Geographical Variations in Equality of Opportunity

Raj Chetty has been leading a tremendously important and (already influential) research project on Social Mobility and the geographical variations in equality of opportunity in the US.

Among the main findings, social mobility is found to vary dramatically across US cities.  These geographical differences are correlated with five factors: segregation, income inequality, local school quality, social capital, and family structure. Check one of their papers, below. The website of the project is here, with links to interactive map/chartthe data used in the project etc.

Chetty, R., et al. (2014). Where is the land of opportunity? The geography of intergenerational mobility in the United States (No. w19843). National Bureau of Economic Research.

[image credit: Chetty et al 2014]

We use administrative records on the incomes of more than 40 million children and their parents to describe three features of intergenerational mobility in the United States. First, we characterize the joint distribution of parent and child income at the national level. The conditional expectation of child income given parent income is linear in percentile ranks. On average, a 10 percentile increase in parent income is associated with a 3.4 percentile increase in a child’s income. Second, intergenerational mobility varies substantially across areas within the U.S. For example, the probability that a child reaches the top quintile of the national income distribution starting from a family in the bottom quintile is 4.4% in Charlotte but 12.9% in San Jose. Third, we explore the factors correlated with upward mobility. High mobility areas have (1) less residential segregation, (2) less income inequality, (3) better primary schools, (4) greater social capital, and (5) greater family stability. While our descriptive analysis does not identify the causal mechanisms that determine upward mobility, the publicly available statistics on intergenerational mobility developed here can facilitate research on such mechanisms.

Monday, April 13, 2015

Quote of the Day

Mahatma Ghandi: "There is more to life than increasing its speed"

[image credit: Sowiesoso]

Related Link:

Friday, April 10, 2015

How Internet Censorship Works in China, or how to create a brilliant research design

A few of months ago, Prof Gary King presented in Oxford a research project where he and his group (J. Pan and M. Roberts) analyze how internet censorship in China works. Judging by his presentation, this is one of the most well designed research pieces I have seen, specially considering the complexity of the topic and the difficulties in grasping censorship practices in a sensitive context. 

This post may look a bit off-topic considering the scope of this blog but I believe we always have something to learn from reading/listening to good research, even if it's not in our field of expertise.  You may watch King's presentation here, and check the papers below. 

King, G., Pan, J., & Roberts, M. E. (2013). How censorship in China allows government criticism but silences collective expression. American Political Science Review, 107(02), 326-343. (ungated version)


We offer the first large scale, multiple source analysis of the outcome of what may be the most extensive effort to selectively censor human expression ever implemented. To do this, we have devised a system to locate, download, and analyze the content of millions of social media posts originating from nearly 1,400 different social media services all over China before the Chinese government is able to find, evaluate, and censor (i.e., remove from the Internet) the large subset they deem objectionable. Using modern computer-assisted text analytic methods that we adapt to and validate in the Chinese language, we compare the substantive content of posts censored to those not censored over time in each of 85 topic areas. Contrary to previous understandings, posts with negative, even vitriolic, criticism of the state, its leaders, and its policies are not more likely to be censored. Instead, we show that the censorship program is aimed at curtailing collective action by silencing comments that represent, reinforce, or spur social mobilization, regardless of content. Censorship is oriented toward attempting to forestall collective activities that are occurring now or may occur in the future --- and, as such, seem to clearly expose government intent.

King, G., Pan, J., & Roberts, M. E. (2014). Reverse-engineering censorship in China: Randomized experimentation and participant observationScience, 345(6199), 1251722. (ungated version)

Existing research on the extensive Chinese censorship organization uses observational methods with well-known limitations. We conducted the first large-scale experimental study of censorship by creating accounts on numerous social media sites, randomly submitting different texts, and observing from a worldwide network of computers which texts were censored and which were not. We also supplemented interviews with confidential sources by creating our own social media site, contracting with Chinese firms to install the same censoring technologies as existing sites, and—with their software, documentation, and even customer support—reverse-engineering how it all works. Our results offer rigorous support for the recent hypothesis that criticisms of the state, its leaders, and their policies are published, whereas posts about real-world events with collective action potential are censored.

Tuesday, April 7, 2015

Dynamic population mapping using mobile phone data

An interesting study by Pierre Deville showing that it is possible to use data from mobile phone networks to analyze population spatial distribution while guaranteeing phone users’ privacy (via Tim Wallace).

Deville, P., et al. (2014). Dynamic population mapping using mobile phone data.Proceedings of the National Academy of Sciences, 111(45), 15888-15893.

During the past few decades, technologies such as remote sensing, geographical information systems, and global positioning systems have transformed the way the distribution of human population is studied and modeled in space and time. However, the mapping of populations remains constrained by the logistics of censuses and surveys. Consequently, spatially detailed changes across scales of days, weeks, or months, or even year to year, are difficult to assess and limit the application of human population maps in situations in which timely information is required, such as disasters, conflicts, or epidemics. Mobile phones (MPs) now have an extremely high penetration rate across the globe, and analyzing the spatiotemporal distribution of MP calls geolocated to the tower level may overcome many limitations of census-based approaches, provided that the use of MP data is properly assessed and calibrated. Using datasets of more than 1 billion MP call records from Portugal and France, we show how spatially and temporarily explicit estimations of population densities can be produced at national scales, and how these estimates compare with outputs produced using alternative human population mapping methods. We also demonstrate how maps of human population changes can be produced over multiple timescales while preserving the anonymity of MP users. With similar data being collected every day by MP network providers across the world, the prospect of being able to map contemporary and changing human population distributions over relatively short intervals exists, paving the way for new applications and a near real-time understanding of patterns and processes in human geography.

Seasonal changes in population distribution in Portugal and France