This paper presents a new probabilistic method of record linkage, developed using the U.S. full count censuses of 1900 and 1910 but applicable to a range of different sources of historical records. The method was designed to exploit a more comprehensive set of individual and contextual characteristics present in historical census data, aiming to obtain a machine learning algorithm that better distinguishes between multiple potential matches. Our results demonstrate that the method achieves a match rate that is twice as high other currently popular methods in the literature while at the same time also achieving greater accuracy. In addition, the method only performs negligibly worse than other algorithms in resembling the target population.

IPUMS-International www.ipums.org/international disseminates harmonized census microdata for more than 80 countries at no cost, although access is restricted to bona-fide researchers and students who agree to the stringent conditions of use license. Currently over 270 samples are available, totalling more than 600 million person records. Each year 15-20 additional samples are released, as more countries cooperate with the IPUMS initiative and the integration of 2010 round census samples is completed. With so much microdata so readily available, questions of data quality naturally arise. This paper focusses on the concept of statistical coherence over time for a single concept, primary schooling completed. From an analysis of the percentage completing primary schooling by birth year for pairs of samples for thirteen Asia-Pacific countries, we find outstanding coherence for four-China, Mongolia, Vietnam, and Indonesia-with mean differences of less than 0.5 percentage points, regression coefficient (b) ranging from 0.93 to 1.07 and R2 =.99. For the thirteen countries as a group there is considerable variation overall with mean absolute difference as high as 16 percentage points, b ranging from 0.62-1.44 and R2=.65-.99. As a whole, statistical coherence of primary schooling is outstanding. Nonetheless, to make expert use of the harmonized microdata, researchers are cautioned to carefully study the IPUMS integrated metadata as well as the original source documentation. National Statistical Offices not currently cooperating or that have not yet entrusted 2010 round census microdata are invited to do so.

The Integrated Public Use Microdata Series (IPUMS)-International partnership is a project of the Minnesota Population Center and national statistical agencies, dedicated to collecting and distributing census data from around the world. IPUMS is currently disseminating data on over a half-billion persons enumerated in more than 250 census samples from 79 countries. The data series includes information on a broad range of population characteristics, including fertility, nuptiality, life-course transitions, migration, labor-force participation, occupational structure, education, ethnicity, and household composition. This paper describes sample characteristics and data structure; the data integration process including the creation of constructed family interrelationship variables; the flexible dissemination system that enables researchers to build customized extracts of pooled census samples across time and place; and some of the most significant findings that have emerged from the database.

IPUMS-International is the world's largest collection of high-precision census data samples containing individual-level information on 544 million people in 74 countries spanning five decades. These data are available for download at no cost to educators, students and researchers for scholarly, educational, and policy-related analysis. The database, built in cooperation with national statistical offices, provides remarkable access to data for educators wishing to expose students to real-world governmental statistics. Variables with distinct census responses for each person are coded consistently across time and place; documentation is thorough, harmonized and easily accessible; and the web delivery system allows registered users to create and download customized data sets pooled across time and place. Individual level responses mean that data can be used in analyses that range from simple descriptive tables to advanced statistical modeling.

The IPUMS-International partnership is led by the University of Minnesota Population Center in consortium, at present, with 101 official statistical agencies that have endorsed uniform protocols for world-wide access to microdata free-of-cost (https://international.ipums.org/international/international_partners.shtml). In 2014, the partnership is celebrating its fifteenth year with the launch of 259 integrated, confidentialized samples representing 79 countries (82% of the worlds population) and totaling 561,622,889 person records. More than 9,000 researchers have made over 50,000 extracts from the IPUMS-International database and published nearly a thousand papers, reports, dissertations and books using the microdata. Research output will continue to grow as 2010 round census samples and other types of microdata (surveys on demography, health, labor force, etc.) are integrated into the IPUMS dissemination system. Through the IPUMS partnership the value of census microdata is enhanced for both producers (official statisticians) and users (researchers and policy makers) in three important ways: 1) Dissemination: one portal with a single set of rules and internet browser tools provides access to microdata for all researchers, regardless of country of residence; 2) Security: privacy and confidentiality are protected by rigorous technical, administrative and legal protocols; and 3) Usefulness: both metadata and microdata are integrated to preserve the definitions and concepts in each census to facilitate good use.

Fifty years ago, census microdata were available for only a handful of countries and trans-border access was difficult for all but a few. Now, from www.ipums.org, many decades of census microdata for much of the globe are readily accessible anywhere, free of cost to researchers and students - regardless of country of birth, residence, or citizenship. As of late - 2013, 238 samples representing 74 countries, totaling more than one half billion person records and encompassing more than four fifths of the world's population are available to more than 7,000 registered researchers worldwide. Pioneers of demography developed national and even regional databases for analyzing census microdata (Ruggles 2013), but it is IPUMS that developed the first integrated system for global access. The IPUMS big data revolution, foretold a decade ago (McCaa and Ruggles 2002), has arrived, but is not yet complete. 50 years hence it is likely that almost all census microdata around the globe will be integrated and accessible via multiple systems of access using application programming interfaces (API).The revolution has already sparked much new research. According to a former president of the Population Association of America, students of the Big Census Data Revolution, specifically those with analytical experience using integrated census microdata, enjoy advantages for internships and employment at the World Bank and similar agencies (Meier, Lam, and McCaa 2011). Likewise, Dot-Coms beckon as a new jobs frontier opens for savvy Big Data users (Lohr, 2012:B2).

IPUMS-International disseminates population census microdata at no cost for 69 countries. Currently, a series of 212 samples totaling almost a half billion person records are available to researchers. Registration is required for researchers to gain access to the microdata. Statistics from Google Analytics show that IPUMSInternationals lengthy, probing registration form is an effective deterrent for unqualified applicants. To protect data privacy, we rely principally on sampling, suppression of geographic detail, swapping of records across geographic boundaries, and other minimally harmful methods such as top and bottom coding. We do not use excessively perturbative methods. A recent case of perturbation gone wrong the household samples of the 2000 census of the USA (PUMS), the 20032006 American Community Survey, and the 20042009 Current Population Survey, an empirical study of the impact of perturbation on the usability of UK census microdatathe Individual SARs of the 1991 census of the UK, and a mathematical demonstration in a timely compendium of statistical confidentiality practices confirm the wisdom of IPUMS microdata management protocols and statistical disclosure controls.

Terra Populus, part of NSFs new DataNet initiative, will develop organizational and technical infrastructure to integrate, preserve, and disseminate data describing changes in the human population and environment over time. A plethora of high-quality environmental and population datasets are available, but they are widely dispersed, have incompatible or inadequate metadata, and have incompatible geographic identifiers. The new infrastructure will enable researchers to identify and merge data from heterogeneous sources to study the relationships between human behavior and the natural world. Terra Populus will partner with data archives, data producers, and data users to create a sustainable international organization that will guarantee preservation and access over multiple decades.

Many statistical offices recognize the need for enhancing access to census microdata. High costs, challenging risks, and low rewards are substantial obstacles to going-it-alone. An economical, essentially cost-free solution, endorsed by more than 90 National Statistical Offices, is offered by the IPUMS-International project. This paper discusses ten ways the project enhances access and adds value to census microdatagrouped into four categories: 1. statistical confidentiality (security, disclosure protections, managing access), 2. Integration (comprehensive source documentation, integrated metadata, integrated, pooled microdata, IPUMS-I constructed variables), 3. Dissemination (free, trans-border access, custom-tailored extracts), and 4. ethics (statistical transparency, academic freedom, reduction of risks of fraud/mis-representation, and sharing of research findings). Statistical agencies not yet participating in the IPUMS-International initiative are invited to do so. Those already participating are encouraged to entrust 2010 round census microdata to the project in a timely manner.

In African countries, census data provide critical information on current and historical trends in households and family relationships. We use data from IPUMS-International and the African Integrated Census Microdata Series (AICMD), a freely available database of 52 million person records from 13 African countries, from the 1980s through the 2000s. Our paper assesses the quality of the data available in each of these censuses for constructing measures of spouse and parent-child relationship, household structure, and estimates of fertility. We consider the quality of age and sex reporting, as well as missing data. We assess the quality of the links created within African censuses and compare estimates of own child fertility in South Africa with other published estimates. We show that the IPUMS pointers perform well and are especially valuablegiven the complex family and household structure found in many African countries.

The Minnesota Population Center (MPC) provides aggregatedata and microdata that have been integrated and harmonized to maximize crosstemporal and cross-spatial comparability. All MPC data products are distributed free of charge through an interactive Web interface that enables users to limit the data and metadata being analyzed to samples and variables of interest to their research. In this article, the authors describe the integrated databases available from the MPC, report on recent additions and enhancements to these data sets, and summarize new online tools and resources that help users to analyze the data over time. They conclude with adescription of the MPCs newest and largest infrastructure project to date: a global population and environment data network.

The Minnesota Population Center (MPC), through the IPUMS-International census microdata project, archives the world's largest stock of census microdata and documentation. A decade of labor assiduously scouring local, national, regional, and international archives on every continent is beginning to bear fruit. Microdata for over 350 censuses for more than 120 countries are safely ensconced in the MPC digital archives. Metadata from more than 900 censuses are catalogued and now being disseminated world-wide without cost in cooperation with National Statistical Institute(NSI) partners and the Integrated Health Survey Network, using the latest international standards for electronic metadata. 5,000 researchers representing more than ninety countries are registered to access confidentialized, integrated microdata without payment and with complete academic freedomthanks to a uniform licensing agreement endorsed by almost one-hundred NSIs. Integration lowers the barriers to entry and facilitates comparative research over space and time.For the future, we plan to integrate and disseminate confidentialized samples of the 2010 round censuses of the sixty-two countries already represented in the database. Samples of an additional 20-30 countries will be released to the global scientific community as time and resources permit. New initiatives are also planned: boundary files for GIS applications, an on-line tabulator forregistered researchers, a secure enclave offering access to full-count microdata at the MPC and perhaps virtual enclaves for partners world-wide with certified secure sites. Several NSI partners have already granted assent for constructing a pilot at the MPC. Before the end of this year, thanks to major funding from the National Science Foundation (USA), a new project, TerraPop, begins--an initiative to combine population microdata with climate and land cover data.

In the last decade, a revolution has occurred in access to census microdata for social and behavioral research. More than 325 million person records (55 countries, 159 samples) representing two-thirds of the worlds population are now readily available to bona fide researchers from the IPUMS-International website: www.ipums.org/international hosted by the Minnesota Population Center. Confidentialized extracts are disseminated on a restricted access basis at no cost to bona fide researchers. Over the next five years, from the microdata already entrusted by National Statistical Office-owners, the database will encompass more than 80 percent of the worlds population (85 countries, ~100 additional datasets) with priority given to samples from the 2010 round of censuses. A profile of the most frequently used samples and variables is described from 64,248 requests for microdata extracts. The development of privacy protection standards by National Statistical Offices, international organizations and academic experts is fundamental to eliciting world-wide cooperation and, thus, to the success of the IPUMS initiative. This paper summarizes the legal, administrative and technical underpinnings of the project, including statistical disclosure controls, as well as the conclusions of a lengthy on-site review by the former Australian Statistician, Mr. Dennis Trewin.

Population microdata are often organized into households, but taking fulladvantage of the hierarchical structure of the data requires identifying the specificfamily interrelationships among household members. Household relationships areexpressed relative to a single reference person and are often ambiguous forpersons outside the nuclear family. The International Integrated Public UseMicrodata Series (IPUMS-International) has developed consistent "pointer"variables for 115 census samples, identifying each person's mother, father andspouse. The database, with over 279 million person records, is freely availablefor downloading by researchers. Some countries collected pointer information asactual census questions, and the IPUMS pointers agree with these data 98% of thetime. Nevertheless, some household situations are more problematic than others,and there is variation in the source materials across countries. Although imperfect,by using these common tools researchers remove the possibility that differingresults across studies are an artifact of different linking procedures.

Integrated census microdata constitute a new resource for social science research and policy making. The IPUMS-International project (www.ipums.org/international) is a global initiative in cooperation with national statistical authorities world-wide to anonymize, integrate and disseminate samples of census microdata. Extracts adapted to the specific research needs of each user are distributed as ASCII textfiles along with the corresponding metadata without charge via the Internet. Researchers analyze the data using their own software and hardware. This paper offers a brief over-view of the project and invites official statistical agencies in Africa to obtain additional information about participating in the IPUMS initiative by emailing the principal author of this paper. To illustrate one possible application for evidence-based policy making with respect to the Millennium Development Goals, microdata from the 2000 census of Mexico are used to measure progress toward the attainment of universal primary education and the elimination of gender inequities in access to primary education.