title: Descriptive statistics: the specification of statistical measures and their presentation in tables and graphs. Part 7 of a series on evaluation of scientific publications.
abstract: BACKGROUND
  Descriptive statistics are an essential part of biometric analysis and a prerequisite for the understanding of further statistical evaluations, including the drawing of inferences. When data are well presented, it is usually obvious whether the author has collected and evaluated them correctly and in keeping with accepted practice in the field.
  
  
  METHODS
  Statistical variables in medicine may be of either the metric (continuous, quantitative) or categorical (nominal, ordinal) type. Easily understandable examples are given. Basic techniques for the statistical description of collected data are presented and illustrated with examples.
  
  
  RESULTS
  The goal of a scientific study must always be clearly defined. The definition of the target value or clinical endpoint determines the level of measurement of the variables in question. Nearly all variables, whatever their level of measurement, can be usefully presented graphically and numerically. The level of measurement determines what types of diagrams and statistical values are appropriate. There are also different ways of presenting combinations of two independent variables graphically and numerically.
  
  
  CONCLUSIONS
  The description of collected data is indispensable. If the data are of good quality, valid and important conclusions can already be drawn when they are properly described. Furthermore, data description provides a basis for inferential statistics.
authors.affiliation: Institut für Medizinische Biometrie, Epidemiologie und Informatik, Johannes Gutenberg-Universität Mainz.
authors.forename: Albert
authors.initials: A
authors.lastname: Spriestersbach
authors.forename: Bernd
authors.initials: B
authors.lastname: Röhrig
authors.forename: Jean-Baptist
authors.initials: JB
authors.lastname: du Prel
authors.forename: Aslihan
authors.initials: A
authors.lastname: Gerhold-Ay
authors.forename: Maria
authors.initials: M
authors.lastname: Blettner
mesh_terms: D001699:Biometry / Q000379:methods*; D003196:Computer Graphics; D003198:Computer Simulation; D003626:Data Display; D003627:Data Interpretation, Statistical; D008954:Models, Biological; D015233:Models, Statistical