STATA

Data Analysis Using STATA: Use and Interpretation

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Stata is a general-purpose statistical software package created in 1985 by StataCorp. The name Stata is a syllabic abbreviation of the words statistics and data. The FAQ for the official forum of Stata insists that the correct English pronunciation of Stata “must remain a mystery”; any of “Stay-ta”, “Sta-ta” or “Stah-ta” (rhymes of the three pronunciations of ‘data’) are considered acceptable. More recent updates indicate that Stata employees pronounce it /ˈsteɪtə/.

Most of its users work in research, especially in the fields of economics, sociology, political science, biomedicine, and epidemiology. According to StataCorp (2016), Stata is “a complete, integrated statistical software package that provides everything you need for data analysis, data management, and graphics”.  Basically, Stata is a software that allows you to store and manage data (large and small data sets), undertake statistical analysis on your data, and create some really nice graphs.

Stata allows you to write code or use menus to perform your analysis. Stata has two primary menu tabs: Graphics and Statistics. Within “Statistics” there are twenty-one sub tabs and numerous tabs within those tabs. Within “Graphics” there are twenty-one tabs as well (you think the people at Stata like to play Black Jack?). I admit, this can be a bit daunting and time consuming if you are trying to find a specific function.  But wait, there’s more. In the command box you can type “help” and what you are looking for. The key point here is I don’t waste time trying to find what I’m looking for. After running the command through the menus method the code shows up in the “Review” box.  I can then copy and paste the command into a “do-file”. A “do-file” is the text document that allows you to submit more than one command to Stata at once.

Stata allows you to have more than one do-file opened at a time. This is a big plus because it makes it easy to copy and paste from other project do-files into the current do-file.  Using do-files is significantly quicker than using the menus if you have created template do-files, especially for creating graphs. There are so many options for creating a graph. It takes less than a minute to copy from a template and paste the commands into your current project. Stata is extremely efficient running repetitive analysis when incorporating macros and loops in a do-file. This sounds like it may be difficult but it’s not.

How well is Stata supported by Stata Corp? On average Stata sends out updated files every two months with new features and/or any fixes to reported glitches. The reference guide for Stata 13 is 281 pages filled with examples and links to the data sets used in the examples. The professional community also provides incredible support. Stata allows third party written commands (also known as modules) to be imported into the software. The website http://ideas.repec.org/s/boc/bocode.html is a warehouse for hundreds of third party written commands which have been tested before made public. Running a search for “logistic” returned 128 results. The bottom line is Stata will run every analysis that the other major statistical packages can, if not more. It is a very efficiently organized program to learn to use.  Third party professionals are continuously offering new functions. Stata adds new features without charging a “new” version fee. All this and the added bonus are reasonably priced and has no add-on charges.

There are four major builds of each version of Stata:

  • Stata/MP for multiprocessor computers (including dual-core and multicore processors)
  • Stata/SE for large databases
  • Stata/IC, which is the standard version
  • Numerics by Stata, supports any of the data sizes listed above in an embedded environment

Small Stata, which was the smaller, student version for educational purchase only, is no longer available. This software is commonly used among health researchers, particularly those working with very large data sets, because it is a powerful software that allows you to do almost anything you like with your data.

It’s important to note that Stata is not the only statistical software – there are many others that you may come across if you pursue a career that requires you to work with data. Some of the other common statistical packages include SPSS and SAS (yes, they all start with ‘s’!).  The focus for this session, however, is on Stata.

Main contentsSee more from basic to advanced

Opening and saving Stata datasets

Opening and saving datasets in Stata works similarly to those tasks in other computer applications. There are a few differences, however. First, it is possible

Finding and Installing New Commands or User-Written Programs in Stata

Stata has a system to disseminate user-written programs that lets it grow continuously. So actually, there are a tremendous number of user-written programs for Stata

Getting help in Stata

Stata’s help system provides a wealth of information to help you learn and use Stata. To find out which Stata command will perform the statistical

Creating new variables in Stata

1. Generate and replace This chapter shows the basics of creating and modifying variables in Stata. We saw how to work with the Data Editor

Listing data and basic command syntax in Stata

1. Command syntax This chapter gives a basic lesson on Stata’s command syntax while showing how to control the appearance of a data list. As

Labeling data in Stata

1. Making data readable This chapter discusses, in brief, labeling of the dataset, variables, and values. Such labeling is critical to careful use of data.

Importing data in Stata

One of the easiest ways to get data into Stata is often overlooked: you can copy data from most applications that understand the concept of

Using the Variables Manager in Stata

1. The Variables Manager This chapter discusses Stata’s Variables Manager. To get started, open the automobile dataset by typing sysuse auto, clear in the Command

Using the Data Editor in Stata

1. The Data Editor The Data Editor gives a spreadsheet-like view of data that are currently in memory. You can use it to enter new

Setting font and window preferences in Stata

1. Changing and saving fonts and sizes and positions of your windows You may find that you would like to change the fonts and display

Saving and printing results by using logs in Stata

1. Using logs in Stata When you work on an analysis, it is worthwhile to behave like a bench scientist and keep a lab notebook

Editing graphs in Stata

1. The Graph Editor With Stata’s Graph Editor, you can change almost anything on your graph; you can add text, lines, arrows, and markers wherever

Graphing data in Stata

1. Working with graphs Stata has a rich system for graphical representation of data. The main command for creating graphs is unsurprisingly named graph. Behind

Using the Do-file Editor—automating Stata

1. The Do-file Editor Stata comes with an integrated text editor called the Do-file Editor, which can be used for many tasks. It gets its

Deleting variables and observations in Stata

1. Clear, drop, and keep In this chapter, we will present the tools for paring observations and variables from a dataset. We saw how to

Typographical Note and Example Stata Session

1. Typographical Note This book employs several typographical conventions as a visual cue to how words are used: ■ Commands typed by the user appear

More on Stata for Windows

1. Using Stata datasets and graphs created on other platforms Stata will open any Stata .dta dataset or .gph graph file regardless of the platform

Advanced Stata usage

1. The Windows Properties Sheet When you double-click on a shortcut to start an application in Windows, you are actually executing instructions defined in the

Troubleshooting Stata

1. If Stata does not start You tried to start Stata and it refused; Stata or your operating system presented a message explaining that something

Updating and extending Stata—Internet functionality

1. Internet functionality in Stata Stata works well with the Internet. Stata can use datasets and view remote help files as though they were on

Learning more about Stata

1. Where to go from here You now know plenty enough to use Stata. There is still much, much more to learn because Stata is

Missing Value Codes in Stata

Examples seen so far involve only a single missing-value code, Stata’s default: a large number which Stata displays as a period. In some datasets, however,

Generating and Replacing Variables in Stata

The generate and replace commands allow us to create new variables or change the values of existing variables. For example, in Canada, as in most

Specifying Subsets of the Data: in and if Qualifiers

Many Stata commands can be restricted to a subset of the data by adding an in or if qualifier. Qualifiers are also available for many

Creating a New Stata Dataset by Copy and Paste

When the original data source is electronic, such as a web page, text file, spreadsheet or word processor document, we can bring these data into

Creating a New Stata Dataset by Typing in Data

Data that were previously saved in Stata format can be retrieved into memory either by typing a command of the form use filename, or by

Stata Documentation and Resources

1. Stata’s Documentation and Help Files The complete Stata 12 Documentation Set includes 19 volumes: a slim Getting Started manual (for example, Getting Started with

Combining Two or More Stata Files

We can combine Stata datasets in two general ways: append a second dataset that contains additional observations, or merge with other datasets that contain new

Importing Data from Other Programs to Stata

Previous sections illustrated how to enter and edit data using the Data Editor. If our original data reside in an appropriately formatted spreadsheet, we just

Using Explicit Subscripts with Variables in Stata

When Stata has data in memory, it also defines certain system variables that describe those data. For example, _N represents the total number of observations.

Creating New Categorical and Ordinal Variables in Stata

A previous section illustrated how to construct a categorical variable called type to distinguish among territories, provinces and nation in our Canadian dataset. You can

Converting Between Numeric and String Formats in Stata

Dataset Canada2.dta contains one string variable, place. It also has a labeled categorical variable, type. Both seem to have nonnumeric values. Beneath the labels, however,

Using Functions in Stata

This section lists many of the functions available for use with generate or replace. For example, we could create a new variable named loginc, equal

Histograms by using Stata

Histograms, displaying the distribution of measurement variables, are most easily produced with their own command histogram. For examples, we return to the data on 194

Writing Programs for Data Management in Stata

Data management on larger projects often involves repetitive or error-prone tasks that are best handled by writing specialized Stata programs. Advanced programming can become very

Creating Random Data and Random Samples in Stata

The pseudo-random number function runiform() lies at the heart of Stata’s ability to generate random data or to sample randomly from the data at hand.

Using Weights in Stata

Stata understands four types of weighting: aweight   Analytical weights, used in weighted least squares (WLS) regression and similar procedures. fweight    Frequency weights, counting the

Reshaping Data in Stata

A different sort of restructuring is possible through the reshape command. This command switches datasets between two basic configurations termed wide and long. Earlier in

Collapsing Data in Stata

Long after a dataset has been created, we might discover that for some purposes it has the wrong organization. Fortunately, several commands facilitate drastic restructuring

Symmetry and Quantile Plots by using Stata

Box plots, bar charts and histograms summarize measurement variable distributions, hiding individual data points to clarify overall patterns. Symmetry and quantile plots, on the other

Bar Charts and Pie Charts by using Stata

The graph bar command, unlike graph twoway bar, works well to display relationships involving one or more categorical variables. Such graphs prove particularly useful with

Other Twoway Plot Types by using Stata

In addition to basic line plots and scatterplots, the graph twoway command can draw a wide variety of other types. This section illustrates several more;

Line Plots and Connected-Line Plots by using Stata

Mechanically, connected-line plots (graph twoway connect) are just scatterplots in which the points are connected by line segments. Line plots (graph twoway line) show the

Scatterplots and Overlays by using Stata

Scatterplots belong to a broad family called twoway graphs. Stata’s basic scatterplot command has the form . graph twoway scatter y x where y is

Box Plots by using Stata

Box plots convey information about center, spread, symmetry and outliers at a glance. For example, Figure 3.4 is a simple box plot of adfert (adolescent

Declare Survey Data in Stata

Since 2001, the Granite State Poll at the University of New Hampshire has conducted statewide telephone surveys several times each year. Each survey contacts a

Creative Graphing by using Stata

Edward Tufte, in his elegant and influential books about graphing data (1990, 1997, 2001, 2006), calls for more effort at designing clear, information-packed graphics. Presenting

Graph Editor in Stata

The Graph Editor allows us to alter the appearance of a graph currently in memory, whether just drawn or previously saved and retrieved by graph

Retrieving and Combining Graphs by using Stata

Any graph saved in Stata’s “live” .gph format can subsequently be retrieved into memory by the graph use command. For example, we could retrieve Figure

Graphing with Do-Files by using Stata

Complicated graphics like Figure 3.26 require graph commands that are many physical lines long (although Stata views the whole command as one logical line). Do-files,

Adding Text to Graphs by using Stata

Titles, captions and notes can be added to make graphs more self-explanatory. The default versions of titles and subtitles appear above the data region; notes

Exploratory Data Analysis by using Stata

Statistician John Tukey assembled a toolkit of old and new methods for exploratory data analysis (EDA), which involves analyzing data in an exploratory and skeptical

Summary Statistics for Measurement Variables by using Stata

Dataset electricity.dta contains information on electricity consumption in U.S. states, from the California Energy Commission (2012). To find the mean and standard deviation of per

Bar Charts for Multiple Comparisons by using Stata

The catplot bar charts in Figure 4.3 depict a relationship between two categorical variables, each with four categories. If we have more than two variables,

Survey-Weighted Tables and Graphs by using Stata

The June 2011 Granite State Poll included six questions related to global warming or climate change. Several questions were factual, but one (warmop) asked what

Poststratification Weights of Survey Data in Stata

The previous section gave an example of weights based on the sampling design, which was known before data collection began. A second type of weights

Design Weights of Survey Data in Stata

The previous section took weight definitions for granted, and indeed many data users begin with a completed survey in which weights have already been calculated

One-Sample Tests by using Stata

One-sample t tests have two seemingly different applications: Testing whether a sample mean y differs significantly from an hypothesized value p0 . Testing whether the

Using Frequency Weights with Stata

summarize, tabulate, table and related commands can be used with frequency weights that indicate the number of replicated observations. For example, here are the mean

Tables of Means, Medians and Other Summary Statistics by using Stata

Summary Statistics tabulate produces tables of means and standard deviations within categories of the tabulated variable. For the remaining examples in this chapter, we return

Multiple Tables and Multi-Way Cross-Tabulations by using Stata

With surveys and other large datasets, we sometimes need frequency distributions of many different variables. Instead of asking for each table separately, for example by

Frequency Tables and Two-Way Cross-Tabulations by using Stata

The summary statistics, graphs and transformations described above apply mainly to measurement variables. Categorical variables require different approaches, often starting with simple one- or two-way

Normality Tests and Transformations by using Stata

Many statistical procedures work best when applied to variables that follow normal distributions. The preceding section described exploratory methods to check for approximate normality, extending

Simple Regression by using Stata

File Nations2.dta contains U.N. human-development indicators for 194 countries: . use C:\data\Nations2.dta, clear Life expectancies (life) exhibit much place-to-place variation. For example, Figure 7.1 shows

Predicted Values and Error-Bar Charts by using Stata

After anova , the followup command predict calculates predicted values, residuals or standard errors and diagnostic statistics. One use for such statistics is in drawing

Factor Variables and Analysis of Covariance (ANCOVA) by using Stata

anova and many other Stata estimation commands allow independent variables specified in factor variable notation. The prefix i. written before the name of an independent

Two- and N-Way Analysis of Variance by using Stata

One-way ANOVA examines how the means of measurement variable y vary across categories of one other variable x. N-way ANOVA generalizes this approach to deal

One-Way Analysis of Variance (ANOVA) by using Stata

Analysis of variance (ANOVA) provides another way, more general than t tests, to test for differences among means. The simplest case, one-way ANOVA, tests whether

Two-Sample Tests by using Stata

The remainder of this chapter draws examples from a survey of college undergraduates by Ward and Ault (1990). About 19% of these students belong to