## STAT 13

(Sec. 1a-1c)

Introduction to Statistical Methods for the Life and Health Sciences

## Instructor: Ivo Dinov, Asst. Prof.

Departments of Statistics & Neurology
 http://www.stat.ucla.edu/~dinov/

# Lab 1

Also see: http://www.ats.ucla.edu/stat/stata/webbooks/reg/chapter1/statareg1.htm

# Thursday, Oct. 04, 2001

Lab 1: Getting to Know STATA

# Lab 1: Getting to Know STATA

The purpose of this lab is to get you acquainted with the basics of operating iMacs and to get you started using Stata. By the end of this section you should be able to perform the following tasks:

b)      Enter data into Stata by hand;

c)      Send emails and lab files to your home computer.

Warning: Dealing with a computer is always frustrating. In a class like this, there are varying levels of computer experience, and in a lab like this, even though all of the computers look the same, there are variations in the way things actually behave. Do NOT feel bad if you are confused, or if things don’t work out the way this manual says they should, or if you can’t seem to figure out what to do as quickly as the person next to you. This is all a natural part of the learning process. There are many resources here to help, and people who want to help you. But first you MUST ASK QUESTIONS!

Activity 1: Logging in to the system in the lab (for the first time only):

Important: If you are not officially enrolled in the class or officially on the waiting list, you need to see Jose Garcia to get access to the computer lab AFTER you have been officially enrolled. Jose’s office is located right next to the lab (it’s the first door to the right as you enter the lab).

1)      Type    guest

4)      You’ll see two panels; the “Guest” and “Items for Guest.” Under the “Items for Guest ” panel, double click on the file called “Winter 2001 Roster.url”

5)      Look for your name. Once you find it, you will see a five-digit number next to it.

6)      Write down this number on a piece of paper and keep it on a safe place throughout the quarter. This five-digit number is your lab ID.

7)      Up on your screen, click on “ File” and go to “Quit” to exit Internet Explorer.

8)      You should see on your screen the “Guest” and “Items for Guest” panels. Click on “Special” and go to “Logout.”

9)      Confirm that you want to logout.

How to log in to the system once you have your five-digit lab ID number (this is the procedure you will use from now on):

Now you’ll see a monitor screen with several icons aligned to its right.  Clicking twice on an icon will open it.

What are these icons?

The Macintosh HD icon contains various applications and documents having to do with the hard drive of the computer you are on. However, you will rarely need to access this.

The next two icons are printers. If you have a file you want to print, you can drop and drag it onto this icon and it will print on one of the printers in the back of the room. You may print up to 100 pages each quarter.  Once you exceed this quota, you will be charged for your printing material.

The Macintosh Manager icon contains system administrative items and is not accessible.

The “Items for Students” icon contains, as you might guess, items that might be useful for students in any class that might use this lab.

The icon with your Lab ID number is where your work will be stored. This should be the first place to look for a file.

The trash is where you drag and drop files that you wish to delete. Items will remain in the trash until you “empty” it, and forever after they are gone. To empty the trash, select “Empty Trash” from the “Special” menu item at the top of your screen.

Let’s continue…

4)      Double click on the icon that shows your lab ID number.

5)      Next double click on the icon called “Items for Student.”

6)      You should see a folder called “Student,” where you’ll find the icons for several programs available in your Mac computer, including Stata (a statistical software), Internet Explorer (through which you access the Internet), AppleWorks and Microsoft Word (two different word processors), and WebMail, which you can use to send and receive emails with attached files.

We will be using Stata in this class to analyze data and to assist in understanding some statistical concepts.  Stata is a very sophisticated and powerful computing package that requires two basic ingredients in order to run:  data and commands.  Throughout the quarter, you will learn increasingly complex Stata commands.  You will also learn several different ways to get data into Stata.  This first Lab will teach you some commands concerned with entering data by hand.

Getting Data into Stata

To Start Stata

Double click on “My Stata” found under the “Items for Student” folder. You should see next four windows. They are called “Review,” “Variables,” “Stata Results,” and “Command.”

In the “ Command” window, type edit and press Return.

You’ll see the Stata’s editor, which is like a spreadsheet. The columns correspond to variables and rows to observations.  You navigate by clicking on a cell, or by using the arrow keys.

Activity 2: Entering Data by Hand

This is not something you want to do too often. It can be tedious and tiring. But  sometimes, particularly if you’ve collected your own data, this is the only way to go. Stata has a spreadsheet editor that makes this as easy as possible, and allows you to fix typing mistakes.

Exercise:

A Statistics professor gave a survey to an upper division class. He asked each student for their height (in inches), their sex (m or f), and the number of days since their last alcoholic drink. If they had never had an alcoholic drink they were to enter “never.” The results for a non-random sample of seven of these students are shown below. Each row represents one student’s response to these three questions. Notice that one female student chose not to answer the question about her height. Also, an “n” in the alcohol column means the student answered “never.”

height               sex                   alcohol

68                    m                     n

78                    m                     5

75                    m                     5

63                    f                       3

66                    m                     40

-                       f                       n

60                    f                       18

Please enter this raw data into the Stata spreadsheet.  Note:  Do not enter the variable names “height,” “sex,” and “alcohol” in the spreadsheet editor.  You will name the variables in a different way.

Tip: You skip a cell by pressing on Return on your keyboard.

Give names to the variables:

Once you have typed your data into the Stata’s spreadsheet, it is time to assign names to your variables.

1)      Double click on the first cell of the very first row of the spreadsheet (the darkened one). You’ll see a box called “Stata Variable Information.” For now, you should be concerned only with entering the information under “Name.” In this case, you should type height

2)      Next, click on “OK.”

3)      Now repeat the same procedure when assigning names for the variables “sex” and “alcohol.”

Now that you’ve spent time entering data by hand, you’ll want to save it or else you’ll have to re-enter it the next time you want to analyze the data.

1)      First, you should close the spreadsheet by double clicking on the small box located on the top left side of the spreadsheet window. Once you’ve done that, you should see Stata’s four initial windows again.

2)      Go to “File” and click on “Save.”  You’ll see a box where you’ll be asked to name your file. Usually, researchers choose names that represent the dataset.  In this case, you might choose something like “class,” but the name is totally up to you.  When you type it in, make sure that you keep Stata’s file extension “.dta” before you click on “ Save.”

3)      To exit Stata, go back to “File” and click on “Quit.”

Note: This activity is just for practice. You do not need to turn anything in to your instructor.

Activity 3:  Sending lab files to your home computer

There may be times that you’d like to work on your statistics labwork on another computer.  You’ll notice that there are no disk drives on these iMacs, so it will be impossible to save your files to a disk.  Instead, you can email the relevant files to yourself and have access to them from any computer.  To do that:

1)      Double click on the folder “Items for Student.”

2)      Next, double click on the “WebMail” icon. You’ll see a window that looks like the following one:

3)      Enter your Bruin Online ID, and your password. Notice that this is the same information you normally use to check your emails through “Eudora.”

5)      Once you open the “WebMail” window, click on “New.”

6)      You’ll see a window where you should type the email address to which you want to send your lab files. There you have both the options to type in your message and to attach up to three different files at a time.

7)      Click on “Browse.”

8)      Highlight the folder with your Lab ID number on it. Then click on “Open.”

9)      You’ll see next all the files that you have used in your lab section.

10)   To open a Stata file, double click on the Stata directory.

11)   Highlight the Stata file you want to send in your email, and click on “Open.” You should see the WebMail window back on your screen.

12)   Now just click on “ Send Message.”

13)  To exit WebMail, go to “File” and click on “Quit.”

To make sure that this procedure works, email the Stata file containing the practice dataset to yourself.  Then check your email before next week’s lab to make sure that you received it.  You’ll be able to open a Stata file on any computer on which Stata is installed.

Log Out

·        Do NOT forget to logout from your computer before you leave the lab. Otherwise, other people will not only be able to access your personal files but they will be able to print documents by charging on your paper quota!  To logout, go to the Finder (either hold the mouse button down while the cursor is in the upper right-hand corner of the screen or click once on the desktop background).  Select "log out" under the File menu at the top of the screen.  Do NOT select shutdown!

Computer Lab Schedule

If you wish to work in the lab beyond the time of your section meeting, you may check the lab schedule to know when the room is available. The course schedule for the Stat lab is posted on the Statistics Department home page @ http://www.stat.ucla.edu, under “Calendar.”

END OF SECTION

Everyone should self-assess themselves.
And compare their work to the template solution (this is not a unique solution, just a template)
\Ivo D. Dinov, Ph.D., Departments of Statistics and Neurology, UCLA School of Medicine/