Getting Started with STATA

1. Getting Started with STATA By: Katie Droll

2. Embrace Stata! • Stata is your statistical buddy! • If you put in a bit of effort to learn the basics, you should find the program quite easy and very helpful. • Statistical software can be very intimidating your 1st time around. Stay patient!

3. Results window: This is where non-graphic output is printed Review Window: lists all commands Click on command to rerun Variable Window Enter Commands here! Graph Window: Click on graph & copy into word doc STATA Command Window

4. How do I enter data? • Retrieve data from stored data files: • EASY: Open .dta files from textbook CD-ROM • HARDER: Import ASCII data from .txt or .raw • But also useful outside the context of class • Manually enter variables & data values: • EASY: Use the data editor • HARDER: Use input command • Time consuming if there is a lot of data • Prone to errors: typos!

5. Where is the stored data? • Textbook CD-ROM • Datasets for examples found in chapter examples will be under the appropriate ‘chapter’ folder under Stata • Datasets for homework problems in Appendix B of the book should also be here under ‘exercise’ • On the course website • Under ‘Statistical Computing’ ’Datasets’ • Save the .dta file on your computer

6. Retrieving .DTA files • Command line: use "E:\Stata\exercise\nurshome.dta", clear -OR- • Point and Click: Go to ‘File’ ‘Open…’ Select your CD drive Go to ‘Stata’ ‘exercise’ OR ‘chapn’

7. Importing .txt OR .raw data files • Remove the variable names and any other symbols (such as ‘*’) from the top of the .txt file, then save! Command: infile str20 strvar1 numvar2 using “C:\Unicef.txt" Command Variable names File pathname import data command Command for ‘string’ variable indicating the length

8. Entering data using the editor • Go to Data  Data Editor • Enter your data similar to a spreadsheet program like Excel • Double-click on the variable names (var1) to edit them and add variable labels • Click Preserve, and then close out of the data editor window • You cannot run analyses on this data until you preserve the data and close the data editor! Variable Name

9. input str18 name age “Joe Smith” 15 “Ricky Bobby” 24 “Wilma Flintstone” 27 end input str5 first str10 last age Joe Smith 15 Ricky Bobby 24 Wilma Flintstone 27 end input year cigs 1900 54 1910 151 1920 665 1930 1485 1940 1976 1950 3522 1960 4171 1970 3985 1980 3851 1990 2828 end This tells STATA the variable is string Entering data using input Start data entry Must use “” if there are any spaces in variable Length of string variable Exit data entry

10. Summarizing data list print your dataset to the results window summarize variable  prints summary stats in the results window summarize variable, detail  provides additional summary statistics

11. Lab #1 Main Topics

12. Bar Charts graph bar cigs, over(year) title("Cigarette Consumption Per Person, US") b2(Year) ytitle("number of Cigarettes") ylabel(0(2000)4000)

13. Box plot graph box cigs, title("Cigarette Consumption per Person, US") ytitle("Number of Cigarette") graph box resident, medtype(line) box(1, fcolor(magenta) lcolor(purple)) title(Box plot of Nursing Home Residents)

14. Histogram histogram resident, ytitle(Distribution of Residents) xtitle(Number of residents) title(Histogram of the Distribution of Residents)

15. Save commands! • Open a do editor: Window Do-file Editor New Do-File • Copy and paste commands in this file to save for later use • You can also copy and paste commands into a simple txt file or a word file • Please include important output (results & graphs) in your homework, along with the commands that produced the included output.

16. Saving commands to a log file • Before your Stata session begins, you want to give Stata the following Command: log using "C:\Temp\myfile.log", noproc • After you are done writing your Stata commands, you can close the log file by using the Log button located just below the Prefs menu (it looks like scroll with a traffic light next to it). • From within Stata, you can examine the contents of that Log file with the command: type "C:\Temp\myfile.log" • To run that file as a program (referred to as a "do-file" in Stata), you can simply issue the Stata command: do "C:\Temp\myfile.log"

17. Putting Stata output into homework • Simply highlight what you want from the results window (including the command), then copy [Ctrl-C] and paste [Ctrl-V] into your homework document • To copy and paste graphs, just click on the graph before copying it. You can use [Ctrl-C] or Right-click Copy • After you copy & paste the output into your homework, change the font to a monospace (fixed pitch) font, i.e. fonts in which each character has the same width. This will line up your output! • Examples: Courier New, SAS Monospace

18. Lab #2 Main Topics

19. Labels • Save organ.dta from the website to your computer, and it open in Stata • The names of the afflicted organs are just labels. To see what the raw data look like, you can list them without the labels as follows: list, nolabel • You can see what the association of label and value is by listing the labels: label list

20. Summarizing data by categorical groups • If we want to do some exploratory analysis of our data set, we can at first produce some descriptive statistics for the survival of each organ. To do that we must sort the observation by organ. sort organ • Then we can summarize the data by organ as follows: by organ: summarize survival

21. Side-by-side box plots • We can even generate side-by-side box plots for the survival from diagnosis for each affected organ as follows: graph box survival, by(organ) ytitle("Length of Survival (days from diagnosis)")

22. Creating a new variable as a function of an existing variable • The first conclusion from the box plot is that women with breast cancer have the longest survival. This is consistent with the descriptive statistics produced by the summarize command. • Another conclusion is that the variability in the length of survival is not the same in all cases, with breast and ovarian cancer having a large variability (indicated by the length of the box) while the rest of the cancers have very small variability. This will actually be a problem later on, so taking a transformation of the original survival times. A logarithmic transformation is usually a good bet. We do this as follows: generate lsurv=ln(survival) label var lsurv "Log-transformed survival"

23. Box plot of log survival • To include the overall box plot of survival in the side-by-side box plots, you just add the option total: graph box lsurv, by(organ,total) ytitle("Log-transformed Survival (days from diagnosis)")

24. Histograms by group • We can also generate the histograms of survival time (log-transformed) for each type of cancer as well as total as follows: hist lsurv, freq by(organ, total)

25. Selecting groups to summarize • To get descriptive statistics within only breast and ovarian cancer groups you must use the if statement within the summarize command: by organ: summarize survival if organ==1 | organ==4, detail

26. Especially for Point-and-click People! • If you don’t like entering commands, you can also use the menus in Stata to point and click your way through the analyses. • To summarize data: Data  Describe Data ‘choose an option here’ • Graphs: Graphics  Bar Chart Histogram Box plot ‘and many other options’ • This is a great way to explore the program, and learn about the various capabilities of Stata • Still please remember to include the command from the results window in your homework