An analytic method for randomized trials with informative censoring: Part 1

Consider a randomized trial in which time to the occurrence of a particular disease, say pneumocystis pneumonia in an AIDS trial or breast cancer in a mammographic screening trial, is the failure time of primary interest. Suppose that time to disease is subject to informative censoring by the minimum of time to death, loss to and end of follow-up. In such a trial, the censoring time is observed for all study subjects, including failures. In the presence of informative censoring, it is not possible to consistently estimate the effect of treatment on time to disease without imposing additional non-identifiable assumptions. The goals of this paper are to specify two non-identifiable assumptions that allow one to test for and estimate an effect of treatment on time to disease in the presence of informative censoring. In a companion paper (Robins, 1995), we provide consistent and reasonably efficient semiparametric estimators for the treatment effect under these assumptions. In this paper we largely restrict attention to testing. We propose tests that, like standard weighted-log-rank tests, are asymptotically distribution-free -level tests under the null hypothesis of no causal effect of treatment on time to disease whenever the censoring and failure distributions are conditionally independent given treatment arm. However, our tests remain asymptotically distribution-free -level tests in the presence of informative censoring provided either of our assumptions are true. In contrast, a weighted log-rank test will be an -level test in the presence of informative censoring only if (1) one of our two non-identifiable assumptions hold, and (2) the distribution of time to censoring is the same in the two treatment arms. We also extend our methods to studies of the effect of a treatment on the evolution over time of the mean of a repeated measures outcome, such as CD-4 count.     

Immigration to the Federal Republic of Germany as a demographic and social problem

"Addressing the question of immigration to Western Europe and especially to Germany from east and southeast Europe and from developing countries of the South, this article considers whether such immigration can compensate for reductions in population in developed countries. It is argued that the demographic deficits of an aging population can only be corrected to a limited extent through immigration. Any solution, in order to be effective, must include a simultaneous increase in the birthrates of Germany and other European Community countries. With particular regard to future social development in Germany and the EC, it would be advisable for governments to effect measures that will provide both for controlled admissions of immigrants from outside the EC and an increase in local reproductive capabilities."     

An evaluation of population projection errors for census tracts

"In this article we evaluate the accuracy and bias of projections of total population and population by age group for census tracts in three counties in Florida. We use [U.S. census] data from 1970 and 1980 and several simple extrapolation techniques to produce projections for 1990; we then compare these projections with 1990 census counts and evaluate the differences. For the total sample, we find mean absolute errors of 17%-20% for the three most accurate techniques for projecting total population and find no indication of overall bias. For individual age groups, mean absolute errors range from 20%-29%." This is a revised version of a paper presented at the 1993 Annual Meeting of the Population Association of America.     

Implementing partial least squares

Partial least squares (PLS) regression has been proposed as an alternative regression technique to more traditional approaches such as principal components regression and ridge regression. A number of algorithms have appeared in the literature which have been shown to be equivalent. Someone wishing to implement PLS regression in a programming language or within a statistical package must choose which algorithm to use. We investigate the implementation of univariate PLS algorithms within FORTRAN and the Matlab (1993) and Splus (1992) environments, comparing theoretical measures of execution speed based on flop counts with their observed execution times. We also comment on the ease with which the algorithms may be implemented in the different environments. Finally, we investigate the merits of using the orthogonal invariance of PLS regression to improve the algorithms.     

A cultural economy perspective on service sector migration in the global city: the case of Hong Kong

This article argues that in order to fully understand the geography of labour migration to global cities, it is necessary to consider economic forces in conjunction with mediating socio-cultural influences. Support for this argument is based on an examination of the pattern of migration to Hong Kong, a city which plays a significant role in the world economy.
Reported here are the results of an analysis of recently released 1996 by-census data, and the authors' interviews with foreign domestic workers in Hong Kong. These findings have shown that highly skilled immigrant workers were drawn largely from developed countries, the main sources of inward investment in this city, while less skilled immigrants were drawn from less developed neighbouring labour markets.
While the geographical pattern of immigration followed broadly that predicted from Hong Kong's position in the world economy, the results have revealed that cultural influences such as language and social networks are also important in shaping the economic roles of migrant workers.     

Home,work and community: skilled international migration and expatriate women in Singapore

While skilled labour migration across international borders is a phenomenon of increasing significance in the age of globalization and an important component in the production of global cities, it has not been given sufficient attention in traditional migration analyses.
Recent research has focused on institutional mechanisms regulating the patterns of skill transfer rather than the individual experience of being part of the international labour circuit. Women, in particular, have usually been relegated to the role of "trailing spouses" and are generally invisible in the migration process.
Using a questionnaire survey and in-depth interviews, this article attempts to reinstate the importance of women's roles by portraying them as active agents who adopt a range of strategies in negotiating the move and coming to terms with the transformations wrought by the move in the domains of home, work and community. It argues that skilled labour migration is a strongly gendered process, producing different sets of experiences for the men and women involved in it.
While international circulation often represents "career moves" for expatriate men, their spouses often experience a devalorization of their productive functions and a relegation to the domestic sphere. As an adaptive strategy, expatriate women often turn to the social and community sphere to reach for grounding in their lives.
The article also points to the diversity of "expatriate experiences": while "western" expatriates tend to recreate a more exclusive world by drawing on strong institutional support, "Asian" expatriates find that they have to navigate much finer social and cultural divides between themselves and the host society.     

Do Migrants Worsen the Current Account?

There is some concern in Australia that immigration contributes to a widening of its current account deficit. Several cross-section studies have found that migrant households have a lower saving rate than the local born households. In conjunction with a well-known national income identity that the current account deficit is equal to the excess of investment over saving, such findings have been interpreted by many to mean that the migrants contribute to increasing the level of foreign liabilities at a rate greater than that by the local-born.
However, it should be realized that immigration impacts on the economy in a complex way through various demand and supply side channels. Its direct and chain effects on such variables as the current account are spread over both the short and the long term. These effects are neither unidirectional nor always easy to isolate. The final outcome, which is the sum total of all the effects, is uncertain, and cannot be fully understood from a knowledge of cross-sectional saving performance alone.
This article utilizes aggregate time series data to investigate the relationship between the current account and immigration. It finds that although an increase in net migration tends to raise the current account deficit, the longer term effect of immigration on the current account is negligible.     

Occupational status and mobility among undocumented immigrants by gender

Immigration has long been a national and state concern. The 1989 Legalized Population Survey (LPS-1) collected data on illegal immigrants to the US who subsequently became legalized aliens under the provisions of the 1986 Immigration Reform and Control Act. These data are used in a study assessing whether undocumented male and female immigrants improve their earnings and occupational status over time and the extent of variation in occupational status and mobility by gender and region. The data indicate that both undocumented men and women, on average, improved their earnings and occupational status between their first jobs in the US and their jobs just before applying for legalization under the 1986 Immigration Reform and Control Act. However, the earnings, occupational status, and occupational mobility of men were greater than for women.