stata 介绍与命令

VHM-811
Introduction to Stata
1
21 Small Steps to Get You Started The following table outlines 21 simple steps that will get you started using Stata. These exercises use a dataset (nocardia.dta) that has already been saved in Stata format. These data are a subset of the data from a case-control study of Nocardia mastitis carried out in Nova Scotia. A description of the dataset is attached below. Step 1 2 3 Command Description and Examples / KEY pwd tells you what the current working directory is cd changes the current working directory cd c:\nova05\data use opens a dataset use nocardia Note: Open in the File menu does not change the default directory Note: When a file is open, it means that Stata has loaded it into memory and everything done to that file only happens on the copy in memory. We will talk about saving changes permanently later. describe describes a dataset list list the contents of a dataset Note: if there is more than 1 screen full of data .... HR moves you on one line, space bar moves you on one screen, BREAK stops the display) browse brings up a spreadsheet-like data browser that you can use to look at your data (but not make changes to it). If you need to edit your data use the -edit- command sum summary statistics for a dataset sum sum casecont numcow prod by casecont: sum sum casecont, d by casecont: sum numcow, d HELP invokes the on-screen help Note: You can search for all help on a certain subject or go directly to look for help on a specific command. Lets look up -summarize-. tab tabulate (or crosstabulate) categorical variables tab dbarn tab dbarn dclox gen generates a new variable gen bscc_ln=log(bscc) Note: See the attached sheet “Data Manipulations in Stata” for more details and other options save takes the dataset in memory and saves it to a disk file save noc2 if you don’t specify a new name you will have to issue the command: save, replace
Ultimately, you want to use -do- files for all of your research work because it is the only way that you can exactly reproduce any analyses that you have done. To move you in this direction, we will primarily use the “Command” box (ie type in commands), but if you are stuck, you can use the menus.
4 5 6 78 9Βιβλιοθήκη 1011VHM-811
Introduction to Stata
2
Step 12
13 14 15
16
17
18
19 20 21
Command Description and Examples / KEY replace replaces the contents of a new variable gen db=1 if dbarn==2 replace db=2 if dbarn==1 replace db=2 if dbarn==3 Note: When assigning a value to a variable (eg. db=1 means “set db to the value of 1) Stata uses a single equals sign. When evaluating the contents of a variable (eg. dbarn ==2 means “is dbarn exactly equal to 2") Stata uses a double equals sign. LOG click on the “log” button to start up a log file so you can save all of your results. There are two types of log-files (formatted=SMCL and plain text=LOG) - open a plain text log file drop drops variables from the dataset in memory drop db recode recodes categorical variables gen db=dbarn recode db 2=1 1=2 3=2 Note: See the attached sheet “Data Manipulations in Stata” cc case-control study analysis cc casecont dneo cc casecont dneo, by(dclox) Note: cc is just one specific example of the many statistical analysis commands in Stata. Details on all commands can be found in the Reference Manual, or in the on-screen help (which I find much easier to access) cs cohort study analysis cs casecont dneo (Not really legitimate for this dataset since it was a case-control study) egen egen is short for “extension to generate”. It is really a set of programs for carrying out some interesting data manipulations. One of these is -egen cutegen bscc_c4=cut(bscc), at(0 100 200 300 999) This command tells Stata to cut up the variable bscc into categories and create a new variable which I chose to call bscc_c4. The option “at” tells it where to make the cuts and you specify the left hand end of each range plus the right hand end of the highest range (any value bigger than the largest data point will do - I chose 999) scatter generates scatterplots (simple two way graphs) scatter prod bscc scatter prod bscc, by(dclox) regress this performs linear regression reg prod bscc for details see the sheet titled “Linear Regression in Stata” note adds notes (for documentation purposes) directly into the dataset. Notes may relate to the whole dataset or to a specific variable. note: These data are from the Ferns/Dohoo study note db: TS This variable is tie-stall vs other housing types notes Note: The capital letters TS add a time stamp to a note. Introduction to Stata 3