Stata Tutorial First, go to Professor Berman’s website: http://www.econ.ucsd.edu/~elib/120b/ and download the coffee.dta file (right click and save it somewhere) Second, open Stata (Go to the Start Menu and find Stata). You should see: - The output window - The command window - The review of commands - The variable list *Clickability: using your mouse to click on any variable in the variable list will automatically enter it into the command window. Similarly, clicking on any past command in the review of commands will also automatically enter it into the command window. In the examples below, the basic Stata commands are in bold and you type them into the command window. Remember that some of the examples (such as loading the data) require you to enter your own parts of commands (e.g. a file name when loading the data). Loading Data If in Stata Format (like our coffee data): use "C:\Documents and Settings\Leah\My Documents\UCSD\Econ 120B - W 08\coffee08.dta", clear ** Remember that you must include quotation marks (“s) around your file name If in Excel or text format (i.e. notepad): insheet using "C:\Documents and Settings\Leah\My Documents\UCSD\Econ 120B - W 08\coffee.txt" insheet using "C:\Documents and Settings\Leah\My Documents\UCSD\Econ 120B - W 08\coffee.csv" ** Remember that Excel data MUST be saved in the .csv format (“save as”, if not already in that format). You can also enter the data manually (or copy and paste from Excel or almost any format) by typing editand then simply enter or paste your data into the columns and close the window when you finish. If you choose this option, Stata will automatically name your variables by column, e.g. the variable first column is “var1”. To change this, you can rename your variables by typing rename var1 price Inspecting and Describing Data To see the actual observations in the output window: list price quantity +------------------+ | price quantity | |------------------| 1. | 0 160 | 2. | .4 35 | 3. | .5 35 | 4. | .75 23 | 5. | .9 18 | |------------------| 6. | 1 16 | 7. | 1.25 7 | 8. | 1.4 6 | 9. | 1.5 5 | 10. | 1.6 4 | |------------------| 11. | 1.75 4 | 12. | 2 4 | 13. | 2.1 2 | 14. | 2.25 1 | 15. | 2.5 0 | +------------------+ or if there are a lot of observations: browse price quantity which opens a new window displaying the data you specify above To see summary (descriptive statistics like the number of observations, the sample average and standard deviation, etc.) of the data. summarize price quantity Variable | Obs Mean Std. Dev. Min Max -------------+-------------------------------------------------------- price | 15 1.326667 .7318925 0 2.5 quantity | 15 21.33333 40.08503 0 160To get a basic plot of the data in the output window: plot quantity price **Write the “y” variable first, then the “x” variable. 160 + | * | c | u | p | s | | o | f | | c | o | f | f | e | e | * * | | * * | * 0 + * * * * * * * * * +----------------------------------------------------------------+ 0 price per cup 2.5 Generating new variables Example: generate new variables that are the log of price and log of quantity. First, write “generate” then give the new variable a name and then describe how to construct it. generate lp=log(price) (1 missing value generated) ** Stata reports 1 missing value because log(0) is undefined and we have an observation at p=0. This shows up as a “.” in Stata. To see this, simply view the data using “browse” or “list”. generate lq=log(quantity) (1 missing value generated)plot lq lp 3.55535 + | * * | | | * | * | * | | l | q | * | * | * | * * * | | | | * | | 0 + * +----------------------------------------------------------------+ -.916291 lp .81093 Notice how the points now seem to form a straight line! Graphing Data We’ve already seen “plot” but if we want the graph in a separate window (e.g. to print easily for your homework assignment), we need to do one of the following: gr7 lq lp scatter lq lp 0 1 2 3 4 5lq-1 -.5 0 .5 1lpline quantity price twowway connect quantity price **If you want to add an extra dependent “y” variable, then just add it in before the “x”. To print any of these graphs, right click on the graph window and select “Print”. **Helpful resource for Stata graphs: http://www.stata.com/support/faqs/graphics/gph/statagraphs.html Basic Regression To run a basic OLS regression: regress lq lp, robust Regression with robust standard errors Number of obs = 13 F( 1, 11) = 57.94 Prob > F = 0.0000 R-squared = 0.8962 Root MSE = .37065 ------------------------------------------------------------------------------ | Robust lq | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- lp | -1.909033 .2508017 -7.61 0.000