Mapping global cropland and field size

A new 1 km global IIASA-IFPRI cropland percentage map for the baseline year 2005 has been developed which integrates a number of individual cropland maps at global to regional to national scales. The individual map products include existing global land cover maps such as GlobCover 2005 and MODIS v.5, regional maps such as AFRICOVER and national maps from mapping agencies and other organizations. The different products are ranked at the national level using crowdsourced data from Geo-Wiki to create a map that reflects the likelihood of cropland. Calibration with national and subnational crop statistics was then undertaken to distribute the cropland within each country and subnational unit. The new IIASA-IFPRI cropland product has been validated using very high-resolution satellite imagery via Geo-Wiki and has an overall accuracy of 82.4%. It has also been compared with the EarthStat cropland product and shows a lower root mean square error on an independent data set collected from Geo-Wiki. The first ever global field size map was produced at the same resolution as the IIASA-IFPRI cropland map based on interpolation of field size data collected via a Geo-Wiki crowdsourcing campaign. A validation exercise of the global field size map revealed satisfactory agreement with control data, particularly given the relatively modest size of the field size data set used to create the map. Both are critical inputs to global agricultural monitoring in the frame of GEOGLAM and will serve the global land modelling and integrated assessment community, in particular for improving land use models that require baseline cropland information. These products are freely available for downloading from the http://cropland.geo-wiki.org website.

Comparing the similarity of responses received from studies in Amazon's Mechanical Turk to studies conducted online and with direct recruitment

Computer and internet based questionnaires have become a standard tool in Human-Computer Interaction research and other related fields, such as psychology and sociology. Amazon’s Mechanical Turk (AMT) service is a new method of recruiting participants and conducting certain types of experiments. This study compares whether participants recruited through AMT give different responses than participants recruited through an online forum or recruited directly on a university campus. Moreover, we compare whether a study conducted within AMT results in different responses compared to a study for which participants are recruited through AMT but which is conducted using an external online questionnaire service. The results of this study show that there is a statistical difference between results obtained from participants recruited through AMT compared to the results from the participant recruited on campus or through online forums. We do, however, argue that this difference is so small that it has no practical consequence. There was no significant difference between running the study within AMT compared to running it with an online questionnaire service. There was no significant difference between results obtained directly from within AMT compared to results obtained in the campus and online forum condition. This may suggest that AMT is a viable and economical option for recruiting participants and for conducting studies as setting up and running a study with AMT generally requires less effort and time compared to other frequently used methods. We discuss our findings as well as limitations of using AMT for empirical studies.

Spatial analysis of suicide mortality in Québec: spatial clustering and area factor correlates

Understanding the spatial distribution of suicide can inform the planning, implementation and evaluation of suicide prevention actions. No previous study has assessed spatial clustering of the different methods of suicide in Quebec. The aim of this study was to assess spatial clustering of suicide in Quebec between 2004 and 2007 and neighborhood level predictors of the clusters. Scan statistics was applied to detect clusters of suicides by method and by sex. Smoothed standardized mortality ratios (SMRs) for suicide for each neighborhood were also estimated and their association with neighborhood characteristics was investigated using the Bayesian hierarchical spatial model. The pattern of suicide rate was different among men and women; men showed higher standardized mortality rates. The most likely clusters of suicide were found in remote rural areas. However, some neighborhoods in urban areas also had noticeable suicide clusters. Firearms suicide was most likely found in remote rural areas while poisoning and hanging suicide methods clustered in urban areas. These findings suggest that it is important to take geographical variations into account in national policy and health services planning.

Blunted hypothalamic-pituitary-adrenal axis and insulin response to psychosocial stress in young adults born preterm at very low birth weight

BACKGROUND

Young adults born preterm at very low birth weight (VLBW, ≤1500 g) have higher levels of cardiovascular risk factors, including impaired glucose regulation, than their term-born peers. This could be mediated through altered hypothalamic-pituitary-adrenal axis (HPAA) response to stress.

OBJECTIVE

To compare HPAA, glucose and insulin responses provoked by psychosocial stress in VLBW subjects versus a comparison group of term-born controls.

DESIGN AND PARTICIPANTS

We studied 54 unimpaired young adults, aged 19-27 years, born at VLBW and a comparison group of 40 adults born at term, group-matched for age, sex and birth hospital, from one regional centre in southern Finland. The participants underwent a standardized psychosocial stress test (Trier Social Stress Test, TSST).

MEASUREMENTS

In conjunction with TSST, we measured salivary cortisol, plasma ACTH, cortisol, glucose and insulin. Data were analysed with mixed-effects model and multiple linear regression analyses.

RESULTS

Baseline concentrations for cortisol, ACTH, insulin and glucose were similar in VLBW and comparison groups. During TSST, analysed with mixed-effects model, overall concentrations of plasma cortisol were 17·2% lower (95% CI; 3·5 to 28·9) in the VLBW group. The VLBW group also had lower salivary (P = 0·04) and plasma cortisol (P = 0·02) responses to TSST. Insulin and glucose concentrations correlated with changes in cortisol concentrations. Accordingly, VLBW subjects had 26·5% lower increment in insulin (95% CI; 9·8-40·1). Analyses were adjusted for age, sex, body mass index, hormonal contraception, menstrual cycle phase, time of day and parental education.

CONCLUSIONS

VLBW adults have lower HPAA responses to psychosocial stress than term-born controls. This is accompanied by a lower insulin response.

Bayesian modeling of the evolution of male height in 18th century Finland from incomplete data

Data on army recruits' height are frequently available and can be used to analyze the economics and welfare of the population in different periods of history. However, such data are not a random sample from the whole population at the time of interest, but instead is skewed since the short men were less likely to be recruited. In statistical terms this means that the data are left-truncated. Although truncation is well-understood in statistics a further complication is that the truncation threshold is not known, may vary from time to time, and auxiliary information on the threshold is not at our disposal. The advantage of the fully Bayesian approach presented here is that both the population height distribution and the truncation are modeled simultaneously. The truncation threshold is allowed to be random and time-specific whilst the height distribution is assumed to change smoothly in time. Thus, in addition to the population height characteristics, we obtain also insight into recruiting criteria over time. Analysis of historical data from Swedish army recruitment in eight time events between 1768 and 1804 has found a declining trend in the mean population height during the inspected time period and also dramatic systematic changes in the recruiting.

Seasonality and ambient temperature at time of conception in term-born individuals - influences on cardiovascular disease and obesity in adult life

Background

The influence of environmental conditions early in life – including temperature and season – on health later in life has so far not attracted much attention.

Objective

Using data from the Helsinki Birth Cohort Study of 13,345 men and women, the influence of temperature and season at month of conception on birth weight, and on cardiovascular diseases and obesity-related traits in later life was studied.

Design

Linear regressions were fitted to examine the relationship between birth weight/obesity-related variables/hypertension and alternatively month of conception and average temperature of month of conception. The incidence of both coronary heart disease and cerebrovascular disease was assumed to follow a Weibull hazard model, and was modelled accordingly using survival analysis techniques.

Results

In women, unusually cold temperatures at month of conception predicted lower body mass index (BMI) and fat percentage, and protected from obesity. Warmer temperatures at month of conception were associated with higher risk for hypertension. In men, warmer temperatures around conception predicted lower BMI. No seasonal influences were detected on obesity-related variables, nor were there seasonal or temperature mediated influences on birth weight, coronary heart disease or cerebrovascular disease observed.

Conclusions

We suggest that ambient temperature has an influence on obesity-related outcomes and hypertension. This merits further study, also with regard to other health outcomes and from a global perspective.

Birth-weight and resting metabolic rate in adulthood - sex-specific differences

INTRODUCTION

Low birth-weight is associated with an increased risk of cardiovascular disease, hypertension, and the metabolic syndrome (MetS) in adulthood. Resting metabolic rate (RMR) has been suggested to be associated with the development of obesity as well as MetS and might be an indirect indicator of sympathetic activity. This study's aim was to examine the association between birth-weight and adult RMR.

METHODS

A total of 896 men and women from the Helsinki Birth Cohort Study born 1934-44, for whom a detailed set of birth records were available, underwent measurement of body composition and RMR in adulthood.

RESULTS

Among women, birth-weight adjusted for age and fat-free mass (FFM) was inversely associated with RMR (r = -0.12; P < 0.01). For men, a u-shaped relationship was observed, both independently and after adjustment for age, fat mass, and FFM (P = 0.05 for final model).

DISCUSSION

The sex-specific differences for the association between birth-weight and adult RMR might partly be explained by differences in the developmental programming of the sympathetic nervous system between men and women. The higher adjusted RMR among those with the lowest birth-weights is consistent with previous evidence of higher sympathetic drive among these individuals.

The regional association of rising type 2 diabetes incidence with magnesium in drinking water among young adults

The incidence of type 2 diabetes is increasing among Finnish young adults. A slightly increased risk in men was found in the north-east and western part of the country. The higher risk areas in women were found in the western coastal area and in eastern Finland. The present register-based study aimed to evaluate the regional association of the incidence of type 2 diabetes among young adults with the concentration of magnesium in local ground water. The association was evaluated using Bayesian modeling of geo-referenced data aggregated into a regular 10 km × 10 km grid cells. No marked association was found, although suggestive findings were detected for magnesium in well water and diabetes in young adult women. The results of this register-based study did not completely rule out the association of well water magnesium with the geographical variation of type 2 diabetes. The incidence of type 2 diabetes was much higher among individuals aged 40 or over. These suggestive findings indicate that the association between magnesium and type 2 diabetes would also be worth examining among individuals over 40 years of age.

The association between salt intake and adult systolic blood pressure is modified by birth weight

BACKGROUND

Epidemiologic evidence suggests that prenatal growth influences adult blood pressure. Nutritional factors, including salt intake, also influence blood pressure. However, it is unknown whether prenatal growth modifies the association between salt intake and blood pressure in later life.

OBJECTIVE

Our aim was to examine whether the relation between salt intake and adult blood pressure is modified by birth weight.

DESIGN

We studied 1512 participants of the Helsinki Birth Cohort Study who were born between 1934 and 1944. Information on birth weight was abstracted from birth records, and preterm births were excluded. During a clinical study, at the mean age of 62 y, blood pressure, weight, and height were measured. Diet was assessed with a validated food-frequency questionnaire. The relation between salt intake and blood pressure was tested by a piecewise multivariate regression analysis with the best fitting breakpoints to birth weight and salt intake.

RESULTS

An inverse association was observed between birth weight and systolic blood pressure (SBP) (P = 0.02). No significant association between salt intake and SBP was observed in the whole study population. Of those whose birth weight was ≤3050 g, a 1-g higher daily salt intake was associated with a 2.48-mm Hg (95% CI: 0.40, 4.52 mm Hg) higher SBP (P = 0.017) until the saturation point of 10 g. Of those whose birth weight exceeded 3050 g, SBP was not significantly associated with salt intake. For diastolic blood pressure, no significant relations were observed.

CONCLUSION

Adult individuals with low birth weight may be particularly sensitive to the blood pressure-raising effect of salt.

Childhood BMI trajectories and the risk of developing young adult-onset diabetes

AIMS/HYPOTHESIS

The aim of this study was to examine the effects of childhood BMI growth dynamics on the risk of developing young adult-onset type 1 and type 2 diabetes.

METHODS

Finnish national healthcare registers were used to identify individuals with diabetes diagnosed between 1992 and 1996 at 15-39 years of age. Non-diabetic control participants were chosen from the National Population Registry. Anthropometric measurements were obtained from the original child welfare clinic records. Only the case-control pairs with sufficient growth data recorded were included in the analyses (218/1,388 for type 1 diabetes [16%] and 64/1,121 for type 2 diabetes [6%]). Two developmental stages in BMI growth (the points of infancy maximum BMI and the BMI rebound) were examined, and conditional logistic regression was applied to the variables of interest.

RESULTS

The risk for type 1 diabetes increased 1.19-fold per 1 kg/m(2) rise in the infancy maximum BMI (p = 0.02). In addition, there was a 1.77-fold increase in the risk for type 2 diabetes per 1 kg/m(2) rise in the level of BMI at the BMI rebound (p = 0.04). Higher values of BMI at these points corresponded to a larger BMI gain from birth to that developmental stage. Age at the infancy maximum BMI or age at the BMI rebound did not affect the risk for either type of diabetes.

CONCLUSIONS/INTERPRETATION

The BMI gain in infancy among individuals who subsequently developed young adult-onset type 1 diabetes was faster than that of those who remained healthy. The excess BMI gain in individuals who developed young adult-onset type 2 diabetes could already be seen during early childhood.

Genetic random effects model for family data with long-term survivors: analysis of diabetic nephropathy in type 1 diabetes

A shared and additive genetic variance component-long-term survivor (LTS) model for familial aggregation studies of complex diseases with variable age-at-onset phenotype and non-susceptible subjects in the study cohort is proposed. LTS has been used from the early 1970s, especially in epidemiological studies of cancer. The LTS model utilizes information on the age at onset (survival) distribution to make inference on partially latent susceptibility. Bayesian modeling with uninformative priors is used and estimates of the posterior distribution of age at onset and susceptibility parameters of interest have been obtained using Bayesian Markov chain Monte Carlo (MCMC) methods with OpenBugs program. A simulation study confirms that we obtain posterior estimates of the model parameters on shared and genetic variance components of age at onset and susceptibility with good coverage rates. Further, we analyze familial aggregation of diabetic nephropathy (DN) in large Finnish cohort of 528 sibships with type 1 diabetes (T1D). According to the variance components estimated a substantial familial variation in the susceptibility to DN exist among families, while time to DN is less influenced by shared familial factors.

The effect of birth order and parental age on the risk of type 1 and 2 diabetes among young adults

AIMS/HYPOTHESIS

The aim of this study was to examine the effects of birth order and parental age on the risk of type 1 and type 2 diabetes among Finnish individuals aged 15-39 years.

METHODS

Data on all cases of type 1 diabetes (n = 1,345) and type 2 diabetes (n = 1,072), diagnosed between 1992 and 1996, were collected from four sources: standardised national reports from diabetes nurses, the National Hospital Discharge Register, the Drug Prescription Register and the Drug Reimbursement Register. Information on matched controls and the family members of all study subjects were obtained from the National Population Registry. The odds ratios (ORs) for both types of diabetes were estimated using a conditional logistic regression model.

RESULTS

There was a U-shaped relationship between maternal age and the risk of type 2 diabetes in the offspring: the risk was higher in children born to young and old mothers compared with children born to mothers aged around 30 years. The children born second (OR 0.76, 95% CI 0.62-0.94), third (OR 0.73, 95% CI 0.55-0.95), or fourth (OR 0.66, 95% CI 0.47-0.94) had a lower risk of type 2 diabetes than the first-born children. Maternal age, paternal age, and birth order did not have an effect on the risk of type 1 diabetes in the individuals aged 15-39 years at the time of diagnosis.

CONCLUSIONS/INTERPRETATION

Maternal age and birth order are both associated with the risk of early-onset type 2 diabetes. However, part of these associations may be due to low birthweight. In this study neither parental age nor birth order showed a significant association with the risk of type 1 diabetes diagnosed after 15 years of age.