STATA 11 for Windows SAMPLE SESSION - Food Security Group ...

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Stata 11 Sample Session Section 2 – Restructuring Data Files – Table Lookup & Aggregation Step 3: Merge the two files created in steps 1 & 2 to compute calories produced per adult equivalent. The merge command 5. Run the describe command again. To verify that this variable was created, summarize the variable ae. 1. Statistics then Summaries, tables and tests then Summary and Descriptive Statistics then Summary Statistics 2. Variable is ae 3. Don’t forget to copy the command into the do-file editor, then click on the Ok button. You should find that the average adult equivalent over all households is 3.49. The Stata commands are: label variable ae "Adult equivalents per household" summarize ae This completes step 2. Save this file as HH-FILE2.DTA. 1. Click on File/Save As... 2. Filename is hh-file2 3. Click on the Save button. 4. Copy the command from the Results window and paste it into the do-file editor, delete the reference to the directory, and add a comment to explain what you have done. The Stata command is: save "hh-file2.dta" If you run the syntax again and try to save the “hh-file2.dta”, you will get an error message. To save to a file that already exists on the hard disk, an additional subcommand must be added, “, replace” save "hh-file2.dta", replace We have created two files: hh-file1.dta, which contains the calorie-production data for all households, and hhfile2.dta, which contains the adult-equivalent data for all households. We need to combine these files case-by-case matching by district, village and household, to get both sets of data into one file. To do this, we use Combine datasets / Merge two datasets under the Data menu choice. 72
Stata 11 Sample Session Section 2 – Restructuring Data Files – Table Lookup & Aggregation We noted earlier that key variables are required for any merge. When you're joining two files which are at the same data level, as we're about to do, it may not seem important to include key variables, but it is. The key variables determine which observations are to be combined. Note: You should never use Combine datasets without Key Variables because without them you have no guarantee that the program will combine the cases in the manner that you wish. The command will execute without any warnings or error messages, but the results may be incorrect. At this point, if you have not closed Stata, hh-file2.dta is still the working file. A very important point: Stata cannot merge two datasets unless they are both sorted in the order of the key variables. One way to check to see if Stata knows the file is sorted is to use the Describe command. In the Results window you can see at the end of the list of variables, the words “sorted by” and the list of variables that the file is sorted by. Because we created hh-file1.dta by collapsing the file, it is already sorted by district, vil and hh. hhfile2.dta was also created by collapsing the file so it is also sorted by district, vil and hh. We are ready to merge the two files. 1. Select Data then Combine datasets then Merge Two datasets The Merge - Merge dataset in memory with dataset on disk dialog box will appear. The default type of merge is one-to-one on key variables – this is the merge we want to do. 2. We are doing a one to one on key variables – type of merge, the default selection. For the Filename of dataset on disk box, click on the Browse button. Select the file hh-file1.dta and click on Open 3. In the Key variables (match variables) box, select district vil hh These are the Key Variables 4. Click on the Options tab. Under this tab, you see the box labeled Specify new name of variable to mark result of merge The default name is _merge. This variable received a code of 1 or 2 or 3 to describe what type of merge occurred. The code definition is: 73
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STATA 11 for Windows SAMPLE SESSION - Food Security Group ...

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