Stata intro

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Introduction to Stata
Christopher F Baum
Faculty Micro Resource Center Boston College

August 2011

Christopher F Baum (Boston College FMRC)

Introduction to Stata

August 2011

1 / 157

Strengths of Stata

What is Stata?

Overview of the Stata environment

Stata is a full-featured statistical programming language for Windows, Mac OS X, Unix and Linux. It can be considered a“stat package,” like SAS, SPSS, RATS, or eViews. Stata is available in several versions: Stata/IC (the standard version), Stata/SE (an extended version) and Stata/MP (for multiprocessing). The major difference between the versions is the number of variables allowed in memory, which is limited to 2,047 in standard Stata/IC, but can be much larger in Stata/SE or Stata/MP. The number of observations inany version is limited only by memory.

Christopher F Baum (Boston College FMRC)

Introduction to Stata

August 2011

2 / 157

Strengths of Stata

What is Stata?

Stata/SE relaxes the Stata/IC constraint on the number of variables, while Stata/MP is the multiprocessor version, capable of utilizing 2, 4, 8... processors available on a single computer. Stata/IC will meet most users’needs; if you have access to Stata/SE or Stata/MP, you can use that program to create a subset of a large survey dataset with fewer than 2,047 variables. Stata runs on all 64-bit operating systems, and can access larger datasets on a 64-bit OS, which can address a larger memory space. All versions of Stata provide the full set of features and commands: there are no special add-ons or ‘toolboxes’.Each copy of Stata includes a complete set of manuals (over 6,000 pages) in PDF format, hyperlinked to the on-line help.

Christopher F Baum (Boston College FMRC)

Introduction to Stata

August 2011

3 / 157

Strengths of Stata

What is Stata?

A Stata license may be used on any machine which supports Stata (Mac OS X, Windows, Linux): there are no machine-specific licenses for Stataversions 11 or 12. You may install Stata on a home and office machine, as long as they are not used concurrently. Licenses can be either annual or perpetual. Stata works differently than some other packages in requiring that the entire dataset to be analyzed must reside in memory. This brings a considerable speed advantage, but implies that you may need more RAM (memory) on your computer. There are32-bit and 64-bit versions of Stata, with the major difference being the amount of memory that the operating system can allocate to Stata (or any other application).

Christopher F Baum (Boston College FMRC)

Introduction to Stata

August 2011

4 / 157

Strengths of Stata

What is Stata?

In some cases, the memory requirement may be of little concern. Stata is capable of holdingdata very efficiently, and even a quite sizable dataset (e.g., more than one million observations on 20–30 variables) may only require 500 Mb or so. You should take advantage of the compress command, which will check to see whether each variable may be held in fewer bytes than its current allocation. For instance, indicator (dummy) variables and categorical variables with fewer than 100 levels can beheld in a single byte, and integers less than 32,000 can be held in two bytes: see help datatypes for details. By default, floating-point numbers are held in four bytes, providing about seven digits of accuracy. Some other statistical programs routinely use eight bytes to store all numeric variables.

Christopher F Baum (Boston College FMRC)

Introduction to Stata

August 2011

5 / 157 Strengths of Stata

What is Stata?

The memory available to Stata may be considerably less than the amount of RAM installed on your computer. If you have a 32-bit operating system, it does not matter that you might have 4 Gb or more of RAM installed; Stata will only be able to access about 1 Gb, depending on other processes’ demands. To make most effective use of Stata with large...
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