Housekeeping:

1
Session 2

• Housekeeping
• Variable labels, value labels, calculations and
  recoding

2
Review

• You have used Stata
• Largely through the menus and dialogues
• But also with a few commands
• We hope you found it (surprisingly?) easy
• Discuss
• what you liked
• And difficulties so far

3
Housekeeping tasks

• By housekeeping, we mean
• the small jobs to organise and add labels to the
  data
• They make life easier later.
• This includes
• labelling and adding notes to datasets
• labelling variables
• labelling categories (or values) taken by the
  variable
• recoding variables and dealing with codes for
  missing values
• using log files to keep a record of what you have
  done.

4
Labels and notes

Open the file named E_HouseholdComposition.dta Use
Data ? Labels ? Label dataset
5
Dialogue for labelling data set

Type in dialogue as below or use the
command label data Young Lives Study
4
6
Labelling variables
Use the menu sequence Data ? Labels ? Label
variable as shown below

• Or type the command
• label variable relcare "What is your relationship
  to child?

7
Defining value labels

• Use
• Data ? Labels ? Label values
• ? Define or modify value labels
• and complete the dialogue box that follows.

• The corresponding commands show that two steps
  are needed to label the values.
• First, a label must be defined,e.g.
• label define sexlabel 1 "male" 2 "female"
• Then this label is attached to the variable,
• e.g. for the variable called sex use the command
• label values sex sexlabel

8
Your turn

• Work through Section 4.1of the Stata Guide
• Note down any difficulties you have and clarify
  your difficulties with a resource person

9
Recoding a variable
Data ? Create or change variables ? Other
variable transformation commands ? Recode
categorical variable
Also use options to define a new variable
10
Information on the recoded variable

• Always safer to recode into a new variable,e.g.
  seedad2.
• The effect of the recoding can be seen by typing
• codebook seedad2
• If seedad is later no longer needed, it can be
  dropped.
• Use File ? Save, to save information on the new
  variable in the data set.

11
Your turn again

• Work through Section 4.2 of the Stata Guide
• Note down any difficulties you have and clarify
  your difficulties with a resource person

12
Missing values

• Symbols for missing values in Stata
• . and .a .b .c and so on, up to
  .z
• These are used to distinguish between the
  different reasons for values to be missing.
• When making calculations, comparisons or sorting,
  the following rules are observed
• all non-missing numbers are less than .
• . is less than .a
• .a is less than .b, and so on, up to .z

13
Memory

• The initial memory in Stata is 1 megabyte
• This can be changed, but first type Clear to
  clear memory
• To increase the current memory to 20 mbytes, type
• set memory 20m
• For setting Permanent memory, use
• set memory 20m, permanently
• For problems processing large datasets, use the
  compress command.

14
Log files

• To keep a record of the output, while using Stata
• Open a log file by clicking on the Log icon.
• This opens a dialogue
• In your working directory
• so you can name the log file
• It suggests an extension smcl
• .smcl stands for Stata Markup and Control
  Language.

• Log files in Stata record both commands and
  output.

15
Remarks

• You can change the extension to log to produce
  a simple ASCII file
• Other packages use the idea of a log file to
  record just the command not the output as well
• You can do this in Stata (but not from the menus)
• Notice that the command Stata used for its log
  file was
• . log using name of file
• Do the same again, but using
• . cmdlog using name of file
• If at a later stage you need to append or replace
  this file, add the option replace or append at
  the end of the above commands.

16
Your turn

• Practice the above ideas by working through
  Sections 4.6, 4.7, 4.8 of the Stata Guide.
• Then either read your own data into Stata
• and perform some simple analyses using methods
  covered so far
• Or use a dataset suggested by the resource
  persons.

17
So if you have a dataset

• Open, within Stata, the data file in Stata
  formatthat you created in the previous session.
• Identify the key variables in your data set and
  set up labels for each of these variables.
• Identify any categorical variables in your data
  set. Then define, and set value labels that
  describe the levels for each categorical
  variable.
• Finally, re-save your data file.