Lecture 1 Getting Started with SAS

Transcription

1 SAS for Data Management, Analysis, and Reporting Lecture 1 Getting Started with SAS Portions reproduced with permission of SAS Institute Inc., Cary, NC, USA

2 Goals of the course To provide skills required of MS level statisticians Ph.D. statisticians in industry, government, and consulting To provide experience with aspects of applied statistics that may not be covered in other courses

3 Critical features of the work of applied statisticians Goal is to contribute to knowledge in the subject area and to get right answers and contribute to right decisions. All aspects of experimental design and statistical analysis must be correct. appropriate sampling scheme data values must be correct appropriate statistical analysis correct computer code clear reporting and interpretation of statistical results

4 Critical features of the work of applied statisticians Most important question always is: Does this make sense?

5 Critical features of the work of applied statisticians Preparing data for analysis usually takes more time and work than doing the actual analysis

6 Aspects emphasized in this course Data preparation reading data from other sources into SAS checking and validating data merging data from multiple sources reorganizing and reformatting data

7 Aspects emphasized in this course Professional-looking graphical and numerical summaries of data and statistical results. Writing and documenting SAS code. Some written interpretation of results.

8 Data checking and validation- cleaning data sets Making sure that raw data were accurately entered into a computer-readable file Checking that character variables contain only valid values Checking that numeric values are within predetermined ranges Checking whether there are missing values for variables where complete data are necessary Checking for and eliminating duplicate records

9 Data checking and validation- cleaning data sets Checking for uniqueness of certain values, such as patient IDs Checking for invalid date values Checking that an ID number is present in each of several related files Verifying that more complex multi-file rules have been followed

10 SAS Software Foundation SAS is a highly flexible and integrated software environment that can be used in virtually any settings to access, manipulate, manage, store, analyze, and report on data.

11 SAS Software SAS is the statistical software package most commonly used in business, government, and many other applied research settings has the best data management capabilities can handle huge datasets not as user-friendly or well-designed as R or S-PLUS in some other ways R or S-PLUS are often preferred for research in theoretical and methodological statistics

12 Formatting and documenting SAS code Make sure your SAS programs are readable and understandable to yourself (now and if you go back to the program 5 years from now!) to your instructor or supervisor to someone who takes over you job when you quit

13 Formatting and documenting SAS code Use meaningful variable names gender rather than x 1 Use white space Skip lines between logical blocks of code Indent for understandability

14 Formatting and documenting SAS code Document code Program headings program name and where it is on computer programmer's name date of last update purpose of program input files if any output files if any Comments describing blocks of codes. Do if it is not obvious.

15 SAS Programs What is a SAS program? A SAS program is a sequence of steps that the user submits for execution.

16 SAS Programs DATA steps are typically used to create SAS data sets. PROC steps are typically used to process SAS data sets (that is, generate reports and graphs, manage data, and sort data).

17 SAS Programs Raw Data SAS Data Set DATA Step SAS Data Set PROC Step Report

18 Step Boundaries SAS steps begin with either of the following: a DATA statement a PROC statement SAS detects the end of a step when it encounters one of the following: a RUN statement (for most steps) a QUIT statement (for some procedures) the beginning of another step (DATA statement or PROC statement)

19 SAS Statements SAS programs communicate with the computer by means of SAS Statements There are several kinds of statements and they all end in a semicolon. A semicolon in a SAS program is like a period in English. The most common error found in SAS program is the omission of the semicolon.

20 Running a SAS Program You can invoke SAS in the following ways: interactive mode (for example, SAS windowing environment and SAS Enterprise Guide) batch mode noninteractive mode

21 Accessing SAS In Windows Click on start/all programs/the SAS system/sas 9.3(English) You will get a screen that shows A menu bar A log window A program editor window

22 Accessing SAS In Windows Enter commands and programs in program editor window.

23 SAS Windowing Environment

24 SAS Enterprise Guide

25 Three Primary Windows In the SAS windowing environment, you submit and view the results of a SAS program using three primary windows.

26 Editor Windows

27 Editor Windows

28 SAS Windowing Environment When a program is executed, it produces something called SAS LOG and the SAS OUTPUT. SAS LOG is an annotated copy of your original program without the data listed. Any SAS error messages will be found there, along with the data set that was created.

29 Log Window

30 SAS Windowing Environment The Results of the computations and procedures requested by our PROC statements can be found in the OUTPUT window.

31 Output Window

32 Example Consider the following example Subject Number Gender (M or F) Exam 1 Exam 2 Homework Grade 10 M A 7 M A 4 F B 20 M B 25 F A 14 F C We have five variables collected for each of six subjects. The unit of analysis is referred to as observation and variable represent each piece of information we collect for each observation.

33 Example We want to write a SAS program to read this data set and evaluate the average values for the variables Exam 1 and Exam 2. We start with a Data step to read the data. Note that after reading the data, SAS will produce a temporary SAS data set that it will use for calculating the average score.

34 Example How are we going to name the variables? Variable Name Must start with a letter or the underscore character( ) and must not be more than 32 characters (letters, underscores, or digits.) Use of blanks or special character, such as comma, semicolons, etc. are not allowed. Our column headings of Subject Number or Exam 1 are not valid SAS variable names.

35 Example Logical SAS variable names for this collection of data would be: Subject Gender Exam1 Exam2 HW_Grade The data step codes are in the following slide.

36 Example General form of a simple DATA step 1 2 3

37 Example Line 1 tells the program that we want to create a SAS data set called TEST The next two lines (line 2) show an input statement that gives the program two pieces of information What to call the variables Where to find them on the data line SAS understands this is a single SAS statement because there is a single semicolon at the end of it.

38 Example The data line statement (line 3) indicates that the data statements are done and the next thing the program should look for are the data themselves. The next six lines are the actual data. In this example we are including the data line directly in the program. Later we will learn how to read data from external files.

39 Example A SAS program knows that the data lines are completed when it finds a semicolon on the line below the last line of data. Suggestions when putting together the data lines: Put each new observation on a new line. Some times it is necessary to put more than one line per observation. This is no problem.

40 Example Suggestions when putting together the data lines: Line up your variables. Right-justify your numeric values

41 Example Proc Step Suppose we are interested in getting the class means for the two exams. To do this we need to add the following Proc statement to our DATA step exmple.

42 Example 4 5

43 Example The SAS statement 4 is a proc statement indicating what procedure to run. We place the option DATA = Test specifying that this procedure should compute statistics on the data set called Test. If this option omitted then the procedure will use the most recent data set. It is best to use this option on every procedure since in more advanced SAS program, you can have procedures that create data sets as well as many data sets floating around.

44 Example By including this option you always be sure your procedure is operating on the correct data set. The mean procedure calculates the mean for any variable you specify. If you do not list the variable names, the SAS software will calculate the mean and several other statistics for every numeric variable in the data set.

45 Example The RUN statement (number 5) tells SAS that there are no more statements for the preceding procedure and to go ahead and do the calculations. If we have several PROCs in a row, we need only a single RUN statement at the end of the program. However it is recommended to end every procedure with a run statement.

46 Syntax of SAS procedures SAS procedures have options Statements Statements can also have options The syntax for all SAS procedures

47 Syntax of SAS procedures Procedures start with the word PROC followed by the Procedure name. Options are placed, in any order, between the Proc Name and the semicolon separated by spaces. Most procedures need statements to supply more information about which type of analysis to perform.

48 Syntax of SAS procedures Statements follow the procedure, in any order (Except for certain statistical procedures such as ANOVA or GLM). They each end with a semicolon. Some procedure statements also have options. Statement options are placed between the statement keyword and semicolon and are separated by a slash.

49 Syntax of SAS procedures Here is an example

50 Syntax of SAS procedures Here is the Output

51 Comment Statements One of the most important SAS statements is the Comment statement A comment, inserted in a program is one or more lines of text that are ignored by the program. They are to help the programmer or researcher when he/she reads the program at a later date. A properly commented program indicates that a true professional is at work.

52 Comment Statements There are two ways to insert comments into a SAS program. Begin the comment statement with an asterisk (*) and end it with a semicolon. Begin a comment with a /* and ends with a */. This form can be embedded within a SAS statement and can include semicolons.

53 Comment Statements

54 Comment Statements

55 Comment Statements