Wage shocks and consumption variability in Mexico during the 1990s

This paper presents evidence on the relationship between shocks to relative male wages, and changes in household consumption in Mexico during the 1990s decade, which is a period characterized by high volatility. Apart from performing analysis of this type for Mexico for the first time, the paper has mainly two contributions. The first is the use of alternative data sources to construct instrumental variables for wages. The second is to examine differences across four consumption categories: non-durable goods, durable goods, education and health. Our results for non-durable goods consumption reject the hypothesis that Mexican households are able to insure idiosyncratic risk. For the comparisons across consumption categories, the conclusion is that households in Mexico tend to react to temporary shocks by contracting the consumption of goods that represents longer run investment in human capital, which makes them more vulnerable in the future

Using randomized experiments and structural models for 'scaling up': evidence from the PROGRESA evaluation

The evaluation of welfare programs and more generally government or international organisms interventions is often posed as a one off question, in that evaluators ask whether a specific intervention achieves a specific objective in a specific situation. However,recently, the more general question of whether results from a given studies can be used to predict the effect of different interventions in,possibly,different contexts has received a considerable amount of attention. The usefulness of such an exercise, if successful, is obvious. The ability to extrapolate success stories and avoid failures in different situations would obviously be highly desirable. Unfortunately, a rigorous and successful extrapolation is extremely difficult. Perhaps such difficulties should not be unexpected,given the problems that often one encounters in establishing the effects of social programs in non experimental settings. In this paper we discuss at length the issues involved with the evaluation of social interventions and with the attempts at 'scaling them up'. In particular, we discuss the relative merits of non- parametric evaluation strategies that rely on (possibly experimental) exogenous variation to estimate the impact effects and of more structural approaches. The difference between the two approaches is particularly relevant when one comes to the issue of 'extrapolation' and 'scaling up'. In principle one could consider two types of extrapolation and scaling up. First, one might want to predict the effects of a program that is different from the one that was evaluated or the effect of changing some aspects of the program evaluated. Second, one might want to predict the effect of exporting an existing program from a population where its effects were evaluated (evaluation population) to a different population (implementation population). In what follow we focus on the latter problem and discuss the former only marginally. After considering extensively the conceptual and technical issues involved with this type of exercises, we apply the ideas we discuss to the results from the evaluation of PROGRESA , a large welfare program in Mexico, for which a randomized evaluation sample is available and has been extensively studied. In particular, we divide the seven Mexican states in which the evaluation was carried out in two groups and check to what extent the results in one group can be extrapolated to the other. The advantage of such a strategy is that one can compare the extrapolation results (based on a structural model) with the actual 'ex-post' evaluation that can be carried out either by simple comparison of means or by structural methods

Using randomised experiments and structural models for 'scaling up': evidence from the PROGRESA evaluation

The evaluation of welfare programs and more generally government or international organisma interventions is often posed as a one off question, in that evaluators ask whether a specific intervention achieves a specific objective in a specific situation. However, recently, the more general questions of whether results from a given study can be used to predict the the effect of different interventions in, possibly, different contexts has received a considerable amount of attention. The usefulness of such an exercise, if successful, is obvious. The ability to extrapolate success stories and avoid failures in different situation would obviously be highly desirable. Unfortunately a rigorous and successful extrapolation is extremely difficult. In this paper we discuss the issues involved with the evaluation of social interventions and with the attempts at 'scaling them up'. In particular we discuss the realtive merits of non-parametric evaluation strategies that rely on (possibly experimental) exogenous variation to estimate the impact effects and of more structural approaches. The difference between the two appraoches is particularly relevant when one comes to the issue of 'extrapolation' and 'scaling up'. One could consider two types of extrapolation: (i) Predict the effects of a program that is different from the one that was evaluated; (ii) predict the effect of exporting an existing program from a context where is was evaluated to a different one. In this paper we focus on the latter problem. After discussing the conceptual and technical issues, we apply the ideas we discuss to the results from the evluation of PROGRESA, a large welfare program in Mexico, for which a randomized evaluation sample is available and has been extensively studied. In particular, we divide the seven Mexican states in which the evaluation was carried out into two groups and check to what extent the results in one group can be extrapolated to the others

Seasonal variation in sex-specific immunity in wild birds

Whilst the immune system often varies seasonally and exhibits differences between males and females, the general patterns in seasonality and sex differences across taxa have remained controversial. Birds are excellent model organisms to assess these patterns, because the immune system of many species is well characterised. We conducted a meta-analysis using 41 wild bird species from 24 avian families to investigate sex differences and seasonal (breeding/non-breeding) variations in immune status, including white blood cell counts, phytohaemagglutinin (PHA) test, bacteria-killing ability (BKA), haemolysis and haemagglutination assays. We found male-biased macrophage concentration, BKA and haemolysis titers, but only during the breeding season. Sexspecific heterophil concentrations, heterophil/lymphocyte ratios and PHA responses differed between breeding and non-breeding, suggesting larger changes in males than in females. Importantly, sex differences in immune status are stronger during the breeding period than during the non-breeding period. Taken together, our study suggests that both seasonal variation and sex differences in immune system are common in birds, although their associations are more complex than previously thoughtPeer reviewe

Seasonal variation in sex-specific immunity in wild birds

Whilst the immune system often varies seasonally and exhibits differences between males and females, the general patterns in seasonality and sex differences across taxa have remained controversial. Birds are excellent model organisms to assess these patterns, because the immune system of many species is well characterised. We conducted a meta-analysis using 41 wild bird species from 24 avian families to investigate sex differences and seasonal (breeding/non-breeding) variations in immune status, including white blood cell counts, phytohaemagglutinin (PHA) test, bacteria-killing ability (BKA), haemolysis and haemagglutination assays. We found male-biased macrophage concentration, BKA and haemolysis titers, but only during the breeding season. Sex-specific heterophil concentrations, heterophil/lymphocyte ratios and PHA responses differed between breeding and non-breeding, suggesting larger changes in males than in females. Importantly, sex differences in immune status are stronger during the breeding period than during the non-breeding period. Taken together, our study suggests that both seasonal variation and sex differences in immune system are common in birds, although their associations are more complex than previously thought