EMJ series on statistics and methods: variables, populations and samples

This the first article in the EMJ Series on Statistics and Methods describes "variables" which represent different demographic and clinical characteristics of several individuals in a data set. Various attributes of quantitative and qualitative variables, including type, scale of measurement and values they may take are presented. Some descriptive statistics and graphic summaries are introduced. Pertinent examples drawn from journal articles are provided. The article also defines "population" as used in statistics and epidemiology and highlights population in size and scope in the context of the research question to be answered. It emphasizes the need for explicitly defining sampling based on the research question in a particular study. In addition, the articles introduces concepts and notations related to parameter and statistic. It highlights the need for using appropriate sampling method in selecting a representative sample of the study population and to be able to make valid inferences and generalizations. It is indicated in this articles that specific issues requiring further details will be addressed in the Series articles in subsequent Issues of EMJ

Dermal exposure sampling methods: an overview

Although a total of 174 and 117 substances have been listed with a skin (Sk) notation in the Regulations for Hazardous Chemical Substances and Regulation 22.9 of the Mine Health and Safety Act respectively; dermal sampling is not used frequently to assess exposure to these substances. A variety of measurement methods and strategies have been developed during the past forty years to assess dermal exposure. These methods include interception methods (also referred to as surrogate skin methods); removal of contaminant (substance) methods and in situ detection methods (also referred to as fluorescent tracer methods). The aim of this paper is to give an overview of the different dermal sampling methods. Furthermore; the applicability of each method for sampling different hazardous chemical substances will be highlighted in order to assist Occupational Hygienists in choosing the correct dermal sampling method

Onchocerciasis distribution and severity in five West African countries

The Onchocerciasis Control Programme in West Africa recently extended its operation to Guinea, Guinea-Bissau, the western part of Mali, Senegal and Sierra Leone. To estimate the number of people infected and blinded by the disease and to determine its distribution and severity in the extension area, 215 villages were selected, using a stratified random sampling procedure, and surveyed. All the relevant entomological information available at the time was used in the sampling procedure and in the selection of 92 non-representative villages that were surveyed to confirm the findings. In addition, the populations of 608 villages were examined to map out in detail the distribution of onchocerciasis in the areas at a high risk of onchocercal blindness. The study estimated that 1,475,367 people were infected and 23,728 were blinded from onchocerciasis out of a rural population of 4,464,183. The northern and western part of the study area and the lower Niger basin presented a low or no risk of onchocercal blindness. The upper Niger basin, the south-central part of Sierra Leone, and three small foci in the Gambia, Bakoye, and lower Niger river basins were areas with a high risk of onchocercal blindness. The other parts of the study area presented a medium risk of onchocercal blindness. By detecting the communities at risk of onchocercal disease this study permits the selection of populations for disease control based on mass distribution of ivermectin, a microfilaricide