Studying the influence of a secondary variable in Collocated Cokriging estimates

In this paper the influence of a secondary variable as a function of the correlation with the primary variable for collocated cokriging is examined. For this study five exhaustive data sets were generated in computer, from which samples with 60 and 104 data points were drawn using the stratified random sampling method. These exhaustive data sets were generated departing from a pair of primary and secondary variables showing a good correlation. Then successive sets were generated by adding an amount of white noise in such a way that the correlation gets poorer. Using these samples, it was possible to find out how primary and secondary information is used to estimate an unsampled location according to the correlation level.

Actividad física, sedentarismo frente a pantallas y su relación en adolescentes

Programa de Doctorado: Actividad Física, Salud y Rendimiento Deportivo

Evaluation of a date rape prevention program for new students in a university setting

The purpose of this study was to design, implement and evaluate the effectiveness of a date rape prevention program among new students at Rice University. Six-hundred and fifteen new students were randomly assigned to one of eight residential colleges or dormitories. The distribution of students to each of the dormitories was carried out in accordance with a stratified random sampling procedure. The study population was divided into strata based on ethnicity, gender, geographical region, and academic major. The number of students randomly assigned to each of the eight dormitories was approximately 75. After this procedure was completed, each of the colleges was randomly selected to either the intervention or control group. A randomized pretest and posttest control group design was used to assess changes in attitudes, self-efficacy, and behavior with regard to date rape. All participants were given an anonymous pretest and posttest measuring attitudes, self-efficacy, and behavior immediately prior to and following the intervention. The intervention group attended the play Scruples, designed to promote date rape prevention, after which they were immediately posttested. After this initial posttest the intervention group also participated in an interactive group role-playing activity led by trained peer instructors. The control group was pretested and subject to the placebo intervention of a multiculturalism play and was posttested immediately afterwards. Later in the week this group saw the Scruples play only. Both control and intervention groups were sent a two month follow-up survey questionnaire, to measure any changes in attitudes, self-efficacy, and behavior over time. As hypothesized students who saw the play Scruples showed a change in attitudes immediately posttest but no difference in self-efficacy or behavior. The two month follow-up survey showed no change in attitudes, self-efficacy, or behavior. There was a difference at pretest in males and females attitudes, with males showing significantly more rape tolerant attitudes than females. Thus, the proposed research findings will provide a better understanding of the attitudes that perpetuate date rape, and will inform strategies for prevention programs. ^

Inclusive education in Spain: how do skills, resources, and supports affect regular education teachers’ perceptions of inclusion?

This study examined regular education teachers’ perceptions of inclusion in elementary and secondary schools in Spain and how these perceptions may differ depending on teaching experience, skills, and the availability of resources and supports. Stratified random sampling procedures were used to draw a representative sample of 336 general education teachers (68 kindergarten, 133 elementary, and 135 secondary teachers) from the province of Alicante. The results indicated the acceptance of the principles of inclusion, although teacher skills, time, material resources, and personal supports for inclusion were deemed insufficient. Kindergarten and elementary teachers showed more positive perceptions of inclusion than secondary education teachers, and so did teachers with more personal supports and material resources than those with less supports and resources. The results are discussed in terms of its implications for practice in order to promote more inclusive classrooms in Spain.

Personal uses and perceived social and economic effects of advertising in Bulgaria and Romania

Purpose - The objective of this paper is to uncover the underlying dimensions of, and examine the similarities and differences in, personal uses of advertising, perceived socio-economic effects of advertising, and consumer beliefs and attitudes toward advertising in Bulgaria and Romania. Moreover, it aims to identify the relative importance of the predictors of attitudes toward advertising in the two countries. Design/methodology/approach - The paper draws upon findings of previous research and theoretical developments by Bauer and Greyser, Sandage and Leckenby, and Pollay and Mittal. The study uses a stratified random sample of 947 face-to-face interviews with adult respondents from major urban areas in Bulgaria (507) and Romania (440). Variables are measured on multi-item scales as a typical application of the reflective indicator model. Findings - Results show that there are significant differences between Romanian and Bulgarian respondents in terms of their attitudes toward advertising. Romanians are more positive about advertising as an institution than the instruments of advertising. Romanians seem to accept the role of advertising in a free market economy, but have less confidence in advertising claims and techniques. Bulgarian respondents seem more sceptical toward advertising in general and are less enthusiastic about embracing the role of advertising as an institution. Moreover, Bulgarians are highly negative towards the instruments advertising uses to convey its messages to consumers. Research limitations/implications - The research findings reflect the views of urban dwellers and may not be generalisable to the wider population of the two countries. Interviewer bias was reduced by eliminating verbal or non-verbal cues to the respondents, and by the use of stratified random sampling. Practical implications - The paper suggests that the regulatory role of codes of advertising practice and industry regulating bodies should be enhanced, and their ability to protect consumers enforced. Marketing campaigns should be more inclusive to involve diverse social groups and reflect generally-accepted social norms. Originality/value - This study reveals that, while general attitudes toward advertising may be similar, attitudes toward the institution and instruments of advertising may differ even in countries with geographic proximity and low cultural distance. © Emerald Group Publishing Limited.

Risk factors for childhood myopia:findings from the NICER study

PURPOSE. We explored risk factors for myopia in 12- to 13-year-old children in Northern Ireland (NI). METHODS. Stratified random sampling was performed to obtain representation of schools and children. Cycloplegia was achieved using cyclopentolate hydrochloride 1%. Distance autorefraction was measured using the Shin-Nippon SRW-5000 device. Height and weight were measured. Parents and children completed a questionnaire, including questions on parental history of myopia, sociodemographic factors, childhood levels of near vision, and physical activity to identify potential risk factors for myopia. Myopia was defined as spherical equivalent ≤0.50 diopters (D) in either eye. RESULTS. Data from 661 white children aged 12-to 13-years showed that regular physical activity was associated with a lower estimated prevalence of myopia compared to sedentary lifestyles (odds ratio [OR] = 0.46 adjusted for age, sex, deprivation score, family size, school type, urbanicity; 95% confidence interval [CI], 0.23–0.90; P for trend = 0.027). The odds of myopia were more than 2.5 times higher among children attending academically-selective schools (adjusted OR = 2.66; 95% CI, 1.48–4.78) compared to nonacademically-selective schools. There was no evidence of an effect of urban versus nonurban environment on the odds of myopia. Compared to children with no myopic parents, children with one or both parents being myopic were 2.91 times (95% CI, 1.54–5.52) and 7.79 times (95% CI, 2.93– 20.67) more likely to have myopia, respectively. CONCLUSIONS. In NI children, parental history of myopia and type of schooling are important determinants of myopia. The association between myopia and an environmental factor, such as physical activity levels, may provide insight into preventive strategies.

Randomized Trial for a Mobile Health Approach to Increase Uptake of Cervical Cancer Screening in Tanzania

Background: Largely due to low availability and uptake of screening in low- and middle-income countries, cervical cancer is the second ranked cancer among women in these countries. This is a tragedy because cervical cancer is one of the most preventable carcinomas. This thesis will investigate behaviour change methods, which capitalize on the recent exponential increase in ownership of mobile phones in Tanzania, to increase uptake of cervical cancer screening (CCS) in the Kilimanjaro region of Tanzania. Objectives: 1) To evaluate the effectiveness of behaviour change messages delivered via short message service (SMS) on the uptake of CCS in the Kilimanjaro region; 2) to evaluate the effectiveness of a transportation eVoucher on the uptake of CCS in the Kilimanjaro region; 3) to explore characteristics associated with CCS uptake in the Kilimanjaro region; and 4) to determine the attitudes towards and perceived benefit of behaviour change SMS messages and eVouchers intended to increase uptake of CCS. Methods: In the Kilimanjaro Region, 853 women participated in a randomized controlled trial. Baseline data was collected through self-report through systematic stratified random sampling. Participants were randomized to one of three groups: a control group, a group receiving behaviour change messages delivered via SMS, or a group receiving a travel eVoucher and identical SMS as the SMS group. A fieldworker recorded participants attending screening at the CCS clinics and administered a post-screening survey. The follow-up period was two months from the time of the participant’s enrolment. Logistic regression (both for the combined and stratified data sets) was used to determine associations between the behaviour change interventions, baseline characteristics and cervical cancer screening uptake. Results: All participants receiving SMS messages (SMS or eVoucher group) were more likely to attend cervical cancer screening in comparison with the control group. 83% of participants who attended screening shared the information contained in the messages with others. Conclusions: Behaviour change messages delivered via SMS and transportation eVouchers have the potential to increase uptake of cervical cancer screening in the Kilimanjaro region of Tanzania. Harnessing this potential will require implementing these interventions alongside other methods to achieve maximum impact.

In-vitro evaluation of the quality of Paracetamol and Co-trimoxazole tablets used in Malawi based on pharmacopoeial standards

Objectives This study was an in-vitro evaluation of different brands of paracetamol and cotrimoxazole tablets, used or found in Malawi, based on Pharmacopoeia standards, in order to ascertain the existence and extent of substandard medicines in Malawi and to give an overview of their distribution in the public and private sectors. Methodology A cross-sectional analytical study was conducted using 11 samples each of paracetamol and cotrimoxazole tablets. Stratified random sampling was used to collect samples. Samples were analyzed using HPLC and Spectrophometric methods as outlined in the BP-2007 and USP-32 at the National Drug Quality Control Laboratory (NDQCL)-Lilongwe (under Pharmacy Medicines and Poisons Board-PMPB) and Orient Pharma Co. Ltd of Taiwan. The results were analyzed using Epi Info. Results and discussion Fifty percent of samples (n=22) were not registered in the country by the PMPB as required by the PMP Act with the majority of those coming from public health facilities. All paracetamol and cotrimoxazole samples complied with identification tests using spectrophotometric and HPLC method. Overall, 27.3% of samples failed to meet the BP-2007 standards for Active Ingredient content, while 22.7% of the samples failed the Friability test. The results from Malawi are similar in magnitude to those within surrounding countries in Africa. Conclusion This pilot study provides objective evidence to show that substandard and unregistered paracetamol and cotrimoxazole are present and being used in Malawi, and thus posing a considerable hazard to public health in Malawi. PMPB, together with the Ministry of Health, must continue to develop a quality assurance system to ensure that medicines are randomly and routinely checked.

Estimating abundance and spatial distribution patterns of the bubble crab Dotilla fenestrata (Crustacea : Brachyura)

The bubble crab Dotilla fenestrata forms very dense populations on the sand flats of the eastern coast of Inhaca Island, Mozambique, making it an interesting biological model to examine spatial distribution patterns and test the relative efficiency of common sampling methods. Due to its apparent ecological importance within the sandy intertidal community, understanding the factors ruling the dynamics of Dotilla populations is also a key issue. In this study, different techniques of estimating crab density are described, and the trends of spatial distribution of the different population categories are shown. The studied populations are arranged in discrete patches located at the well-drained crests of nearly parallel mega sand ripples. For a given sample size, there was an obvious gain in precision by using a stratified random sampling technique, considering discrete patches as strata, compared to the simple random design. Density average and variance differed considerably among patches since juveniles and ovigerous females were found clumped, with higher densities at the lower and upper shore levels, respectively. Burrow counting was found to be an adequate method for large-scale sampling, although consistently underestimating actual crab density by nearly half. Regression analyses suggested that crabs smaller than 2.9 mm carapace width tend to be undetected in visual burrow counts. A visual survey of sampling plots over several patches of a large Dotilla population showed that crab density varied in an interesting oscillating pattern, apparently following the topography of the sand flat. Patches extending to the lower shore contained higher densities than those mostly covering the higher shore. Within-patch density variability also pointed to the same trend, but the density increment towards the lowest shore level varied greatly among the patches compared.

Quantifying recreational shore angling catch and harvest in southern Portugal (north-east Atlantic Ocean): implications for conservation and integrated fisheries management

Recreational shore fishing along 250 km of the south and south-west coast of Portugal was studied based on roving creel and aerial surveys. Surveys were conducted between August 2006 and July 2007, following a stratified random-sampling design and provided information on catch and effort, harvest and discards, angler demographics and fishing habits. Overall, 192 roving creel surveys, 24 aerial surveys and 1321 interviews were conducted. Based on the aerial surveys, a mean +/- s.e. total fishing effort of 705 236 +/- 32 765 angler h year(-1) was estimated, corresponding to 166 430 +/- 9792 fishing trips year(-1). Average time spent per fishing trip was 4.7 h. A total of 48 species, belonging to 22 families, were recorded in roving creel surveys. The most important species was Diplodus sargus, accounting for 44% of the total catches by number and 48% by mass. Estimated mean +/- s.e. total annual recreational shore fishing catch was 160.2 +/- 12.6 t year(-1) (788 049 +/- 54 079 fishes year(-1)), of which 147.4 +/- 11.9 t year(-1) (589 132 +/- 42 360 fishes year(-1)) was retained. Although overall shore-based recreational catches only corresponded to 0.8% of the commercial landings (only common species considered), D. sargus catches by recreational shore anglers were considerable, corresponding to 65% of the commercial landings. The implications of these results for integrated fisheries management and conservation are discussed, and future research proposed.

Integrated soil fertility management in eastern and western Africa: The role of knowledge and innovation systems, its adoption and impact

The rise in population growth, as well as nutrient mining, has contributed to low agricultural productivity in Sub-Saharan Africa (SSA). A plethora of technologies to boost agricultural production have been developed but the dissemination of these agricultural innovations and subsequent uptake by smallholder farmers has remained a challenge. Scientists and philanthropists have adopted the Integrated Soil Fertility Management (ISFM) paradigm as a means to promote sustainable intensification of African farming systems. This comparative study aimed: 1) To assess the efficacy of Agricultural Knowledge and Innovation Systems (AKIS) in East (Kenya) and West (Ghana) Africa in the communication and dissemination of ISFM (Study I); 2) To investigate how specifically soil quality, and more broadly socio-economic status and institutional factors, influence farmer adoption of ISFM (Study II); and 3) To assess the effect of ISFM on maize yield and total household income of smallholder farmers (Study III). To address these aims, a mixed methodology approach was employed for study I. AKIS actors were subjected to social network analysis methods and in-depth interviews. Structured questionnaires were administered to 285 farming households in Tamale and 300 households in Kakamega selected using a stratified random sampling approach. There was a positive relationship between complete ISFM awareness among farmers and weak knowledge ties to both formal and informal actors at both research locations. The Kakamega AKIS revealed a relationship between complete ISFM awareness among farmers and them having strong knowledge ties to formal actors implying that further integration of formal actors with farmers’ local knowledge is crucial for the agricultural development progress. The structured questionnaire was also utilized to answer the query pertaining to study II. Soil samples (0-20 cm depth) were drawn from 322 (Tamale, Ghana) and 459 (Kakamega, Kenya) maize plots and analysed non-destructively for various soil fertility indicators. Ordinal regression modeling was applied to assess the cumulative adoption of ISFM. According to model estimates, soil carbon seemed to preclude farmers from intensifying input use in Tamale, whereas in Kakamega it spurred complete adoption. This varied response by farmers to soil quality conditions is multifaceted. From the Tamale perspective, it is consistent with farmers’ tendency to judiciously allocate scarce resources. Viewed from the Kakamega perspective, it points to a need for farmers here to intensify agricultural production in order to foster food security. In Kakamega, farmers with more acidic soils were more likely to adopt ISFM. Other household and farm-level factors necessary for ISFM adoption included off-farm income, livestock ownership, farmer associations, and market inter-linkages. Finally, in study III a counterfactual model was used to calculate the difference in outcomes (yield and household income) of the treatment (ISFM adoption) in order to estimate causal effects of ISFM adoption. Adoption of ISFM contributed to a yield increase of 16% in both Tamale and Kakamega. The innovation affected total household income only in Tamale, where ISFM adopters had an income gain of 20%. This may be attributable to the different policy contexts under which the two sets of farmers operate. The main recommendations underscored the need to: (1) improve the functioning of AKIS, (2) enhance farmer access to hybrid maize seed and credit, (3) and conduct additional multi-locational studies as farmers operate under varying contexts.

Spatially stratified sampling using auxiliary information for geostatistical mapping

This paper presents a method of spatial sampling based on stratification by Local Moran’s I i calculated using auxiliary information. The sampling technique is compared to other design-based approaches including simple random sampling, systematic sampling on a regular grid, conditional Latin Hypercube sampling and stratified sampling based on auxiliary information, and is illustrated using two different spatial data sets. Each of the samples for the two data sets is interpolated using regression kriging to form a geostatistical map for their respective areas. The proposed technique is shown to be competitive in reproducing specific areas of interest with high accuracy.

Soil carbon stock in the tropical rangelands of Australia: Effects of soil type and grazing pressure, and determination of sampling requirement.

On-going, high-profile public debate about climate change has focussed attention on how to monitor the soil organic carbon stock (C(s)) of rangelands (savannas). Unfortunately, optimal sampling of the rangelands for baseline C(s) - the critical first step towards efficient monitoring - has received relatively little attention to date. Moreover, in the rangelands of tropical Australia relatively little is known about how C(s) is influenced by the practice of cattle grazing. To address these issues we used linear mixed models to: (i) unravel how grazing pressure (over a 12-year period) and soil type have affected C(s) and the stable carbon isotope ratio of soil organic carbon (delta(13)C) (a measure of the relative contributions of C(3) and C(4) vegetation to C(s)); (ii) examine the spatial covariation of C(s) and delta(13)C; and, (iii) explore the amount of soil sampling required to adequately determine baseline C(s). Modelling was done in the context of the material coordinate system for the soil profile, therefore the depths reported, while conventional, are only nominal. Linear mixed models revealed that soil type and grazing pressure interacted to influence C(s) to a depth of 0.3 m in the profile. At a depth of 0.5 m there was no effect of grazing on C(s), but the soil type effect on C(s) was significant. Soil type influenced delta(13)C to a soil depth of 0.5 m but there was no effect of grazing at any depth examined. The linear mixed model also revealed the strong negative correlation of C(s) with delta(13)C, particularly to a depth of 0.1 m in the soil profile. This suggested that increased C(s) at the study site was associated with increased input of C from C(3) trees and shrubs relative to the C(4) perennial grasses; as the latter form the bulk of the cattle diet, we contend that C sequestration may be negatively correlated with forage production. Our baseline C(s) sampling recommendation for cattle-grazing properties of the tropical rangelands of Australia is to: (i) divide the property into units of apparently uniform soil type and grazing management; (ii) use stratified simple random sampling to spread at least 25 soil sampling locations about each unit, with at least two samples collected per stratum. This will be adequate to accurately estimate baseline mean C(s) to within 20% of the true mean, to a nominal depth of 0.3 m in the profile.

An Evaluation of the area stratification used for sampling tunas in the eastern Pacific Ocean and implications for estimating total annual catches

The Inter-American Tropical Tuna Commission (IATTC) staff has been sampling the size distributions of tunas in the eastern Pacific Ocean (EPO) since 1954, and the species composition of the catches since 2000. The IATTC staff use the data from the species composition samples, in conjunction with observer and/or logbook data, and unloading data from the canneries to estimate the total annual catches of yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and bigeye (Thunnus obesus) tunas. These sample data are collected based on a stratified sampling design. I propose an update of the stratification of the EPO into more homogenous areas in order to reduce the variance in the estimates of the total annual catches and incorporate the geographical shifts resulting from the expansion of the floating-object fishery during the 1990s. The sampling model used by the IATTC is a stratified two-stage (cluster) random sampling design with first stage units varying (unequal) in size. The strata are month, area, and set type. Wells, the first cluster stage, are selected to be sampled only if all of the fish were caught in the same month, same area, and same set type. Fish, the second cluster stage, are sampled for lengths, and independently, for species composition of the catch. The EPO is divided into 13 sampling areas, which were defined in 1968, based on the catch distributions of yellowfin and skipjack tunas. This area stratification does not reflect the multi-species, multi-set-type fishery of today. In order to define more homogenous areas, I used agglomerative cluster analysis to look for groupings of the size data and the catch and effort data for 2000–2006. I plotted the results from both datasets against the IATTC Sampling Areas, and then created new areas. I also used the results of the cluster analysis to update the substitution scheme for strata with catch, but no sample. I then calculated the total annual catch (and variance) by species by stratifying the data into new Proposed Sampling Areas and compared the results to those reported by the IATTC. Results showed that re-stratifying the areas produced smaller variances of the catch estimates for some species in some years, but the results were not significant.

A Comparison of Two Stratification Schemes Used in Sampling Canadian Atlantic Cod, Gadus morhua

Sampling is a key element in the assessment of any fish stock. It is often one of the most expensive activities of the management process; thus, improved efficiency can result in significant cost savings. In most cases a two-phase sampling strategy is employed. Two commonly used versions of such stratified random schemes were simulated using a test population based on Atlantic cod, Gadus morhua. A 1 otolith per 1 cm length frequency currently used for many flatfish and some smaller gadoids and a 3 otolith per 3 cm length frequency currently used for many of the larger gadoids. No difference was detected in the age composition or mean length at age for either scheme; however, 10 percent fewer otoliths were collected in 1 for 1 sampling than 3 for 3. There was an improvement of between 30 and 60 percent in the coefficient of variation of the estimated catch numbers at age using the 1 for 1 compared with the 3 for 3 stratified sampling. For these reasons and other operational considerations, the 1 for 1 stratified random design of sampling appears to be superior.