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

ABSTRACT

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