Circular statistics in Stata, revisited

Circular data are a large class of directional data, which are of interest to scientists in many fields, including biologists (movements of migrating animals), meteorologists (winds), geologists (directions of joints and faults), and geomorphologists (landforms, oriented stones). These examples are all recordable as compass bearings relative to North. Other examples include phenomena that are periodic in time, including those dependent on time of day (in biomedical statistics: hospital visits or times of birth) or time of year (in applied economics: unemployment or sales variations). The analysis of circular data is an odd corner of statistical science that many never visit, even though it has a long and curious history. Moreover, it seems that no major statistical language provides direct support for circular statistics. This talk describes the development and use of some routines that have been written in Stata, primarily to allow graphical and exploratory analyses. In 2004, such routines are being rewritten, especially to allow use of the new graphics of Stata 8.

Speaking Stata: Problems with tables, Part I

Tables in some form or another are part and parcel of data management and analysis. The main general-purpose tabulation commands, tabulate, table, and tabstat, are reviewed and compared. When these do not provide a tabulation solution, one key strategy is to prepare the material for tabulation as a set of variables, after which the table itself can be presented with tabdisp or list. This is the first of two papers on this topic. Copyright 2003 by StataCorp LP.tables, tabulate, table, tabstat, tabdisp, list

Speaking Stata: How to face lists with fortitude

Three commands in official Stata, foreach, forvalues, and for, provide structures for cycling through lists of values (variable names, numbers, arbitrary text) and repeating commands using members of those lists in turn. All these commands may be used interactively, and none is restricted to use in Stata programs.They are explained and compared in some detail with a variety of examples.In addition,a self-contained exposition is given on local macros, understanding of which is needed for use of foreach and forvalues. Copyright 2002 by Stata Corporation.foreach, forvalues, for, lists, local macros, substitution first

Speaking Stata: Problems with lists

Various problems in working through lists are discussed in view of changes in Stata 8. for is now undocumented, which provokes a detailed examination of ways of processing lists in parallel with foreach, forvalues, and other devices, including new, concise ways of incrementing and decrementing macros and evaluating other expressions to do with macros in place. New features for manipulating lists held in macros and the new levels command are also reviewed. Copyright 2003 by Stata Corporation.lists, for, foreach, forvalues, levels, macros, tokenize

Speaking Stata: Graphing agreement and disagreement

Many statistical problems involve comparison and, in particular, the assessment of agreement or disagreement between data measured on identical scales. Some commonly used plots are often ineffective in assessing the fine structure of such data, especially scatterplots of highly correlated variables and plots of values measured "before" and "after" using tilted line segments. Valuable alternatives are available using horizontal reference patterns, changes plotted as parallel lines, and parallel coordinates plots. The quantities of interest (usually differences on some scale) should be shown as directly as possible, and the responses of given individuals should be identified as easily as possible. Copyright 2004 by StataCorp LP.graphics, comparison, agreement, paired data, panel data, scatterplot, difference-mean plot, Bland-Altman plot, parallel lines plot, parallel coordinates plot, pairplot, parplot, linkplot, Tukey