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Session 2

Session 2. Housekeeping: Variable labels, value labels, calculations and recoding. 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.

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Session 2

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  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 belowor 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 replaceor 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.

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