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Background Social contact surveys can greatly help in quantifying the heterogeneous patterns of infectious disease transmission. The present study aimed to conduct a contact survey in Japan, offering estimates of contact by age and location and validating a social contact matrix using a seroepidemiological dataset of influenza. Methods An internet-based questionnaire survey was conducted, covering all 47 prefectures in Japan and including a total of 1476 households. The social contact matrix was quantified assuming reciprocity and using the maximum likelihood method. By imposing several parametric assumptions for the next-generation matrix, the empirical seroepidemiological data of influenza A (H1N1) 2009 was analysed and we estimated the basic reproduction number, R 0 . Results In total, the reported number of contacts on weekdays was 10,682 whereas that on weekend days was 8867. Strong age-dependent assortativity was identified. Forty percent of weekday contacts took place at schools or workplaces, but that declined to 14% on weekends. Accounting for the age-dependent heterogeneity with the known social contact matrix, the minimum value of the Akaike information criterion was obtained and R 0 was estimated at 1.45 (95% confidence interval: 1.42, 1.49). Conclusions Survey datasets will be useful for parameterizing the heterogeneous transmission model of various directly transmitted infectious diseases in Japan. Age-dependent assortativity, especially among children, along with numerous contacts in school settings on weekdays implies the potential effectiveness of school closure. Electronic supplementary material The online version of this article (10.1186/s12976-019-0102-8) contains supplementary material, which is available to authorized users.

We present empirical evidence on gender differences in wage returns on firmspecific experience (job tenure) and general experience. We find that overall returns on an extra year of labor market experience are lower for women than men. However, a decomposition analysis shows that the return on job tenure is substantially lower for women than it is for men, and that the return on general experience is higher for women than it is for men. These findings are consistent with the hypothesis that despite their growing attachment to the labor market, women are less likely to invest in job-specific skills or to self-select into jobs with backloaded compensation because women are more prone to job separations than their male counterparts. The lower estimated returns on tenure for women could also be due to employer discrimination in hiring, and the provision of training and promotion opportunities within firms.

The discount rate is a key determinant of investments in human capital and occupational choice. Individuals who are less future oriented -i.e. have a higher discount rate -are less likely to invest in human capital and hence more likely to select into careers with lower and flatter earnings profiles. Since an individual's discount rate is unobservable, we use smoking behavior as a proxy to study the role of discounting on wage dynamics. Using data from the National Longitudinal Surveys of Youth (1979-94) we find that smokers, compared to their non-smoker counterparts, earn lower wages at the time they first enter the labor market and experience substantially lower rates of wage growth in the first decade of their careers. These differences in wage dynamics among smokers and non-smokers are consistent with discounting hypothesis, and highly robust to an extensive array of control variables.2 "I'd like to stop smoking. I have smoked for about 15 years. I was a dancer, and all dancers smoke, it's the most bizarre thing", Newark Jan. 1, '98.

, for many helpful comments and suggestions. We are indebted to Rachel Singal and Jaime Rosenfeld for collecting and analyzing the survey data. The views expressed herein are those of the authors and not necessarily those of the National Bureau of Economic Research.

Lankeshwara MUNASINGHE†a) , Nonmember and Ryutaro ICHISE †b) , Member SUMMARY Link prediction in social networks, such as friendship networks and coauthorship networks, has recently attracted a great deal of attention. There have been numerous attempts to address the problem of link prediction through diverse approaches. In the present paper, we focus on the temporal behavior of the link strength, particularly the relationship between the time stamps of interactions or links and the temporal behavior of link strength and how link strength affects future link evolution. Most previous studies have not sufficiently discussed either the impact of time stamps of the interactions or time stamps of the links on link evolution. The gap between the current time and the time stamps of the interactions or links is also important to link evolution. In the present paper, we introduce a new time-aware feature, referred to as time score, that captures the important aspects of time stamps of interactions and the temporality of the link strengths. We also analyze the effectiveness of time score with different parameter settings for different network data sets. The results of the analysis revealed that the time score was sensitive to different networks and different time measures. We applied time score to two social network data sets, namely, Facebook friendship network data set and a coauthorship network data set. The results revealed a significant improvement in predicting future links.

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Consensus on global warming is the result of multiple and varying lines of evidence, and one key ramification is the increase in frequency of extreme climate events including record high temperatures. Here we develop a metriccalled "record equivalent draws" (RED)-based on record high (low) temperature observations, and show that changes in RED approximate changes in the likelihood of extreme high (low) temperatures. Since we also show that this metric is independent of the specifics of the underlying temperature distributions, RED estimates can be aggregated across different climates to provide a genuinely global assessment of climate change. Using data on monthly average temperatures across the global landmass we find that the frequency of extreme high temperatures increased 10-fold between the first three decades of the last century and the most recent decade (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008). A more disaggregated analysis shows that the increase in frequency of extreme high temperatures is greater in the tropics than in higher latitudes, a pattern that is not indicated by changes in mean temperature. Our RED estimates also suggest concurrent increases in the frequency of both extreme high and Electronic supplementary material The online version of this article (extreme low temperatures during 2002-2008, a period when we observe a plateauing of global mean temperature. Using daily extreme temperature observations, we find that the frequency of extreme high temperatures is greater in the daily minimum temperature time-series compared to the daily maximum temperature time-series. There is no such observable difference in the frequency of extreme low temperatures between the daily minimum and daily maximum.