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

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: 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

Review of Statistical Evaluation of Measurement Errors by Dunn

The new edition of the book by Dunn (2004) is reviewed.measurement errors, linear models, mixed models, gllamm

Speaking Stata: How to repeat yourself without going mad

This column will focus on how to improve your fluency in Stata. Over the next issues we will look at Stata problems of intermediate size which turn out to be soluble with a few command lines. As an introduction, systematic ways of repeating the same or similar operations are surveyed to give one overview of the territory to be covered. Copyright 2001 by Stata Corporation.append, by, collapse, contract, do-files, egen, for, foreach, forvalues, log files, merge, naming conventions, programs, repetition, reshape, statsby, subset or group structure, tabulations

Speaking Stata: How to move step by: step

The by varlist: construct is reviewed, showing how it can be used to tackle a variety of problems with group structure. These range from simply doing some calculations for each of several groups of observations to doing more advanced manipulations making use of the fact that with this construct, subscripts and the built-ins _n and _N are all interpreted within groups. A fairly complete tutorial on numerical evaluation of true and false conditions is included. Copyright 2002 by Stata Corporation.by, sorting, subscripts, true and false

Speaking Stata: Graphing categorical and compositional data

A variety of graphs have been devised for categorical and compositional data, ranging from widely familiar to more unusual displays. Both official Stata commands and user-written programs are available. After a stacking trick for binary responses is explained, bar charts and related displays for cross-tabulations are discussed in detail. Tips and tricks are introduced for plotting cumulative distributions of graded (ordinal) data. Triangular plots are explained for threeway compositions, such as three proportions or percentages. Copyright 2004 by StataCorp LP.graphics, categorical data, binary data, nominal data, ordinal data, grades, compositional data, cross-tabulations, bar charts, cumulative distributions, logit scale, catplot, tabplot, tableplot, distplot, mylabels, triplot