Stata Intro

Practice Exercises

2014 - Debby Kermer, George Mason University Libraries Data Services

Instructions

Create and run syntax to accomplish each task. Press the spacebar to see the next instruction, an answer or a hint.

Open the Pew Social Trends Dataset___ http://dataservices.gmu.edu/files/pew.dtaORFile | Open…

[type in] http://dataservices.gmu.edu/files/pew.dtaORDownload the dataset from:http://www.pewsocialtrends.org/category/datasets/?download=5753

hint usegiven at the workshop

given at the workshop

Exercise 1

Using Help

1

Produce statistics about yrborn using the summarize commandsummarize yrborn

Open the help for that commandhelp summarize

Modify the syntax to…

… use abbreviationssum yrborn orsum yr orsu y

… display additional statisticssum yr, detail

<continues…>

summarize

sum yr, _____hint

1a

Need to create yrborn? generate yrborn = 2005 - age

summarize yrborn

… ignore those who refused to give their age sum yr if (age != 99)sum yr if (age < 99)

Now, summarize age, ignoring those who refused to answersum age if (age < 99)

… and ALSO display additional statisticssum age if (age < 99), detail

sum yr if (________)sum yr if (________)

3 hints

1b

Forgot which value meant refused? label list AGE

Your result should look like ↓ Variable | Obs Mean Std. Dev. Min Max----------+-------------------------------------------------- yrborn | 2948 1963.089 18.01353 1915 1995

Extra Challenge

Compare average age by Region (cregion)tab cregion, sum(age)

Notice how this is a combination of bothtab cregion - frequencies for categorical variables

and sum age - means for numeric variables

But, summarize is used as an option, so the comma and parentheses are necessary

hint

1c

See the help page we used as an example:help tab then tabulate, summarize()

Exercise 2

Indicator Variables

2

generate voted = (________)

codebook ________hint

2a

generate voted = (pvote == 1)

Make a new variable "voted" indicating those who voted in the '04 election. Voters should have a 1, non-voters should have a 0. First, get information about the variable you will use:

codebook pvote04a

Then, create your variable:generate voted ___________

use tab pvote04a voted to check your work:

3 hints

If you want, this is how you can label the variable "voted"

label variable voted "Voted in the '04 Election"

label define yesno 1 "Yes" 0 "No"label values voted yesno

("yesno" is a made-up name, you can use anything)

Now, you try: label the variable "youth" appropriately

lab var youth "Youth: age < 30"

lab def under30 1 "< 30 yrs old" 0 "30 yrs and up"lab val youth under30

2b

Need to create "youth"?generate youth = (age < 30)replace youth = . if (age == 99)

Extra Challenge

In one statement (i.e., one line of syntax), create a variable legal indicating only those of legal drinking age

gen legal = (age >= 21) & (age < 99) gen legal = (age >= 21) if (age < 99)

Although both of the above are good, the values generated by these two commands are not identical. How do they differ?

2c

& recodes 99's as 0if recodes 99's as missing

Legal Drinker

Not Legal

No Age (99)

gen legal = (age >= 21) & (age < 99) 1 0 0gen legal = (age >= 21) if (age < 99) 1 0 .

legal | Freq. ------+------- 1 | 2,842

Exercise 3

Illustrating Relationships

3

3aShow the relationship between age group and voting rate

What variables can you use?youth and voted

What command can you use? Open help.help tab then tabulate twoway

Construct your syntax

tab youth voted___________Use options to include percentages, like this ↓

12

3 hints

| voted youth | 0 1 | Total-------+----------------------+---------- 0 | 18.68 81.32 | 100.00 1 | 47.65 52.35 | 100.00 -------+----------------------+---------- Total | 23.05 76.95 | 100.00

Pearson chi2(1) = 179.6007 Pr = 0.000

Show the relationship between age group and voting rate

tab youth voted, row nofreq chi2

| voted youth | 0 1 | Total-------+----------------------+---------- 0 | 18.68 81.32 | 100.00 1 | 47.65 52.35 | 100.00 -------+----------------------+---------- Total | 23.05 76.95 | 100.00

Pearson chi2(1) = 179.6007 Pr = 0.000

So, is there a relationship between age and voting?Among those younger than 30, 52% voted. But, among those 30 or older, 81% voted. Youth were less likely to have voted (p < .001).

13

hint

• • •

3b

Extra Challenge3c

That's All!

Thanks for trying the Stata Exercises.

If you have any questions about using Statacontact Debby Kermer at dkermer@gmu.eduor see our online resources at:http://dataservices.gmu.edu/software/stata