Peter Sandholt Jensen

Rain, growth and civil war: the importance of location

We re‐examine the Miguel et al. (2004) study of the impact of growth on civil war, using growth in rainfall as an instrument. Miguel et al. (2004) – in our view, erroneously – include countries participating in civil wars in other states. Restricting the conflict data to states with conflict on their own territory reduces the estimated impact of economic growth on civil war. We show how spatial correlations in rainfall growth and participation in civil conflicts induce a stronger apparent relationship in the mis‐classified data.We re‐examine the Miguel et al. (2004) study of the impact of growth on civil war, using growth in rainfall as an instrument. Miguel et al. (2004) – in our view, erroneously – include countries participating in civil wars in other states. Restricting the conflict data to states with conflict on their own territory reduces the estimated impact of economic growth on civil war. We show how spatial correlations in rainfall growth and participation in civil conflicts induce a stronger apparent relationship in the mis‐classified data.

Ultrasound Doppler measurements predict success of treatment with anti-TNF-α drug in patients with rheumatoid arthritis: a prospective cohort study

OBJECTIVE To investigate the predictive ability of core outcomes applied in RA trials, including ultrasound (US) Doppler (USD) measurements differentiating patients who remain on anti-TNF-α therapy following 1 year. METHODS Patients with RA in anti-TNF-α therapy were followed 1 year after therapy initiation. All patients had wrist involvement. At baseline, 2 weeks, 26 weeks and 1 year a USD examination, clinical examination including tender and swollen joint count, visual analogue scale (VAS) global and HAQ, biochemical measures and 28-joint DAS (DAS28) were collected for all patients. The amount of USD signal in the synovium was quantified by measuring the percentage of colour pixels-the colour fraction (CF). Predictive validity for patients who remain on anti-TNF-α therapy after 1 year was assessed for both USD measurements and other disease measures. Baseline values of disease measures of patients who remained on treatment after 1 year was compared with those who stopped therapy. RESULTS The study cohort consisted of 109 patients. In this study, the baseline CF was the only measure predicting which patients would stay on the initial anti-TNF-α therapy for 1 year, evaluated using the square-root of CF (P = 0.024). The other disease markers could not significantly differentiate between the two groups of patients, with P-values of 0.86 and 0.98 for tender and swollen joint count, respectively, 0.86 for CRP, 0.24 for VAS, 0.10 for HAQ and 0.38 for DAS28. CONCLUSION There is now evidence to support that baseline USD, in contrast to clinical measures, can predict which patients will remain on anti-TNF-α 1 year after initiating therapy.

Modern Gender Roles and Agricultural History: The Neolithic Inheritance

This research proposes the hypothesis that societies with long histories of agriculture have less equality in gender roles as a consequence of more patriarchal values and beliefs regarding the proper role of women in society. We test this hypothesis in a world sample of countries, in regions of Europe, and among immigrants and children of immigrants living in the US. This evidence reveals a significant negative relationship between years of agriculture history and female labor force participation rates, as well as other measures of equality in contemporary gender roles. This finding is robust to the inclusion of an extensive set of possible confounders, including historical plough-use and the length of the growing season. We argue that two mechanisms can explain the result: (1) societies with longer agricultural histories had a higher level of technological advancement which in the Malthusian Epoch translated into higher fertility and a diminished role for women outside the home; (2) transition to cereal agriculture requires time consuming processing, and this would tend to be an activity carried out by women.

A Comparison of Different Estimators for Panel Data Sample Selection Models

In this paper, we perform an extensive Monte Carlo study of the finite sample properties of different estimators for panel data sample selection models. The estimators investigated are various two-step estimators and maximum likelihood estimators with simultaneous equations for the samle selection process and the equation of interest. The main result of the Monte Carlo study is that the maximum likelihood estimators of random effects models in general perform better than in two-step estimators

From Open to Secret Ballot: Vote Buying and Modernization

The secret ballot is one of the cornerstones of democracy. We contend that the historical process of modernization caused the switch from open to secret ballot with the underlying mechanism being that income growth, urbanization, and rising education standards undermined vote markets. We undertake event history studies of ballot reform in Western Europe and the U.S. states during the 19th and 20th centuries to establish that modernization was systematically related to ballot reform. We study electoral turnout before and after ballot reform among the U.S. states and British parliamentary constituencies to substantiate the hypothesis that modernization reduced the volume of trade in the vote market.

Long-term effects of weight reduction on the severity of psoriasis in a cohort derived from a randomized trial: a prospective observational follow-up study

BACKGROUND Weight reduction may reduce the severity of psoriasis, but little is known about the long-term effects. OBJECTIVE We aimed to investigate long-term effects of weight reduction in psoriasis. DESIGN We previously conducted a randomized trial (n = 60) involving patients with psoriasis who were allocated to a control group or a low-energy diet (LED) group. Here we followed the participants for an additional 48-wk period. In total, 56 patients with psoriasis [mean ± SD body mass index (in kg/m(2)): 34.4 ± 5.3] underwent a 64-wk weight-loss program consisting of an initial 16-wk randomized phase with an LED for 8 wk and 8 wk of normal food intake combined with 2 LED products/d, followed by a 48-wk period of weight maintenance with the latter diet. After the randomization phase, the control group received the same 8 + 8-wk LED intervention, and all patients were then followed for 48 wk while on the weight-loss maintenance diet. The main outcome was the Psoriasis Area and Severity Index (PASI), and secondary outcome was the Dermatology Life Quality Index (DLQI). RESULTS For the present study, 56 patients were eligible, 38 agreed to participate, and 32 completed. After the 16-wk LED-only period, the mean weight loss was -15.0 kg (95% CI: -16.6, -13.4 kg), and PASI and DLQI were reduced by -2.3 (95% CI: -3.1, -1.5) and -2.3 (95% CI: -3.2, -1.4), respectively. At week 64, the mean weight loss compared with baseline was -10.1 kg (95% CI: -12.0, -8.1 kg), and PASI and DLQI were maintained at -2.9 (95% CI: -3.9, -1.9) and -1.9 (95% CI: -3.0, -0.9), respectively. CONCLUSION Long-term weight loss in patients with psoriasis has long-lasting positive effects on the severity of psoriasis. This trial was registered at clinicaltrials.gov as NCT01137188.

Effect of Weight Loss on the Cardiovascular Risk Profile of Obese Patients with Psoriasis

Psoriasis is associated with obesity and other cardiovascular risk factors including endothelial dysfunction. We aimed to investigate the effects of weight loss on the cardiovascular risk profile of obese patients with psoriasis. A randomised controlled study was conducted in which we measured the microvascular endothelial function with peripheral arterial tonometry (PAT), selected plasma markers of endothelial function, and traditional cardiovascular risk factors in 60 obese patients with psoriasis. The participants were randomised to either low-energy diet (n = 30) providing 800-1,000 kcal/day for 8 weeks followed by 8 weeks of reduced food intake reaching 1,200 kcal/day or normal healthy foods (n = 30) for 16 weeks. The intervention group lost significantly more weight than controls, which resulted in significant reductions of diastolic blood pressure, resting heart rate, total cholesterol, VLDL cholesterol, triglyceride, plasma glucose, glycated haemoglobin, and tissue plasminogen activator inhibitor. Microvascular endothelial function assessed by PAT remained unchanged. We conclude that certain components of the cardiovascular risk profile of obese patients with psoriasis can be significantly improved by weight reduction.

Fertility and Early-Life Mortality: Evidence from Smallpox Vaccination in Sweden

We examine how the introduction of smallpox vaccination affected early-life mortality and fertility in Sweden during the first half of the 19th century. We demonstrate that parishes in counties with higher levels of smallpox mortality prior to the introduction of vaccination experienced a greater decline in infant mortality afterwards. Exploiting this finding in an instrumental-variable approach reveals that this decline had a negative effect on the birth rate, while the number of surviving children and population growth remained unaffected. These results suggest that the decline in early-life mortality cannot account for the onset of the fertility decline in Sweden.

Psoriasis and Obesity

Psoriasis is a common chronic inflammatory skin disease with a complex pathogenesis consisting of a genetic component, immune dysfunction, and environmental factors. It is associated with numerous comorbidities including psoriatic arthritis, cardiovascular disease, metabolic syndrome, and obesity. Evidence suggests that obesity is a risk factor for incident psoriasis, aggravates existing psoriasis, and that weight reduction may improve the severity of psoriasis in overweight individuals. Excess body weight may interfere with the medical treatment used in psoriasis and adds to the cardiovascular risk profile in these patients, which underscores the importance of effective weight control regimens. In this review we examine the current literature with regard to the association between obesity and psoriasis.

On Determining the Importance of a Regressor with Small and Undersized Samples

A problem encountered in, for instance, growth empirics is that the number of explanatory variables is large compared to the number of observations. This makes it infeasible to condition on all variables in order to determine the importance of a variable of interest. We prove identifying assumptions under which the problem is not ill-posed. Under these assumptions, we derive properties of the most commonly used methods: Extreme bounds analysis, Sala-i-Martin’s method, BACE, generalto- specific, minimum t-statistics, BIC and AIC. We propose a new method and show that it has good finite sample properties.