**SAS**

General use. SAS is a package that many "power users" like because of its power and programmability. Because SAS is such a powerful package, it is also one of the most difficult to learn. To use SAS, you write SAS programs that manipulate your data and perform your data analyses. If you make a mistake in a SAS program, it can be hard to see where the error occurred or how to correct it.

Data Management. SAS is very powerful in the area of data management, allowing you to manipulate your data in just about any way possible. SAS includes proc sql that allows you to perform sql queries on your SAS data files. However, it can take a long time to learn and understand data management in SAS and many complex data management tasks can be done using simpler commands in Stata or SPSS. However, SAS can work with many data files at once easing tasks that involve working with multiple files at once. SAS can handle enormous data files up to 32,768 variables and the number of records is generally limited to the size of your hard disk.

Statistical Analysis. SAS performs most general statistical analyses (regression, logistic regression, survival analysis, analysis of variance, factor analysis, multivariate analysis). The greatest strengths of SAS are probably in its ANOVA, mixed model analysis and multivariate analysis, while it is probably weakest in ordinal and multinomial logistic regression (because these commands are especially difficult), robust methods (it is difficult to perform robust regression, or other kinds of robust methods). While there is some support for the analysis of survey data, it is quite limited as compared to Stata.

Graphics. SAS may have the most powerful graphic tools among all of the packages via SAS/Graph. However, SAS/Graph is also very technical and tricky to learn. The graphs are created largely using syntax language; however, SAS 8 does have a point and click interface for creating graphs but it is not as easy to use as SPSS.

Summary. SAS is a package geared towards power users. It has a steep learning curve and can be frustrating at first. However, power users enjoy the its powerful data management and ability to work with numerous data files at once.**Stata**

General Use. Stata is a package that many beginners and power users like because it is both easy to learn and yet very powerful. Stata uses one line commands which can be entered one command at a time (a mode favored by beginners) or can be entered many at a time in a Stata program (a mode favored by power users). Even if you make a mistake in a Stata command, it is often easy to diagnose and correct the error.

Data Management. While the data management capabilities of Stata may not be quite as extensive as those of SAS, Stata has numerous powerful yet very simple data management commands that allows you to perform complex manipulations of your data with ease. However, Stata primarily works with one data file at a time so tasks that involve working with multiple files at once can be cumbersome. With the release of Stata/SE, you can now have up to 32,768 variables in a Stata data file but probably would not want to analyze a data file that exceeds the size of your computers memory.

Statistical Analysis . Stata performs most general statistical analyses (regression, logistic regression, survival analysis, analysis of variance, factor analysis, and some multivariate analysis). The greatest strengths of Stata are probably in regression (it has very easy to use regression diagnostic tools), logistic regression, (add on programs are available that greatly simplify the interpretation of logistic regression results, and ordinal logistic and multinomial logistic regressions are very easy to perform). Stata also has a very nice array of robust methods that are very easy to use, including robust regression, regression with robust standard errors, and many other estimation commands include robust standard errors as well. Stata also excels in the area of survey data analysis offering the ability to analyze survey data for regression, logistic regression, poisson regression, probit regression, etc...). The greatest weaknesses in this area would probably be in the area of analysis of variance and traditional mutivariate methods (e.g. manova, discriminant analysis, etc.).

Graphics. Like SPSS, Stata graphics can be created using Stata commands or using a point and click interface. Unlike SPSS, the graphs cannot be edited using a graph editor. The syntax of the graph commands is the easiest of the three packages and is also the most powerful. Stata graphs are high quality, publication quality graphs. In addition, Stata graphics are very functional for supplementing statistical analysis, for example there are numerous commands that simplify the creation of plots for regression diagnostics.

Summary. Stata offers a good combination of ease of use and power. While Stata is easy to learn, it also has very powerful tools for data management, many cutting edge statistical procedures, the ability to easily download programs developed by other users and the ability to create your own Stata programs that seamlessly become part of Stata.

**SPSS**

General use. SPSS is a package that many beginners enjoy because it is very easy to use. SPSS has a "point and click" interface that allows you to use pulldown menus to select commands that you wish to perform. SPSS does have a "syntax" language which you can learn by "pasting" the syntax from the point and click menus, but the syntax that is pasted is generally overly complicated and often unintuitive.

Data Management. SPSS has a friendly data editor that resembles Excel that allows you to enter your data and attributes of your data (missing values, value labels, etc.) However, SPSS does not have very strong data management tools (although SPSS version 11 added commands for reshaping data files from "wide" format to "long" format, and vice versa). SPSS primarily edits one data file at a time and is not very strong for tasks that involve working with multiple data files at once. SPSS data files can have 4096 variables and the number of records is limited only by your disk space.

Statistical Analysis. SPSS performs most general statistical analyses (regression, logistic regression, survival analysis, analysis of variance, factor analysis, and multivariate analysis). The greatest strengths of SPSS are in the area of analysis of variance (SPSS allows you to perform many kinds of tests of specific effects) and multivariate analysis (e.g. manova, factor analysis, discriminant analysis) and SPSS 11 has added some capabilities for analyzing mixed models. The greatest weakness of SPSS are probably in the absence of robust methods (we know of no abilities to perform robust regression or to obtain robust standard errors), the absence of survey data analysis (we know of no tools in this area).

Graphics. SPSS has a very simple point and click interface for creating graphs and once you create graphs they can be extensively customized via its point and click interface. The graphs are very high quality and can be pasted into other documents (e.g. word documents or powerpoint). SPSS does have a syntax language for creating graphs but many of the features in the point and click interface are not available via the syntax language. The syntax language is more complicated than the language provided by Stata, but probably simpler (but less powerful) than the SAS language.

Summary. SPSS focuses on ease of use (their motto is "real stats, real easy"), and it succeeds in this area. But if you intend to use SPSS as a power user, you may outgrow it over time. SPSS is strong in the area of graphics, but weak in more cutting edge statistical procedures lacking in robust methods and survey methods.

Overall Summary

Each package offers its own unique strengths and weaknesses. As a whole, SAS, Stata and SPSS form a set of tools that can be used for a wide variety of statistical analyses. With Stat/Transfer it is very easy to convert data files from one package to another in just a matter of seconds or minutes. Therefore, there can be quite an advantage to switching from one analysis package to another depending on the nature of your problem. For example, if you were performing analyses using mixed models you might choose SAS, but if you were doing logistic regression you might choose Stata, and if you were doing analysis of variance you might choose SPSS. If you are frequently performing statistical analyses, we would strongly urge you to consider making each one of these packages part of your toolkit for data analysis

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