sas

What is Sas ?

SAS is a programming language that reads the data from a variety of file formats like Excel, flat file, dBase, Lotus,existing SAS dataset(s), or a file produced by another software program. whatever the data SAS has reads , first it will process and then it will performs analyses on the same data .

SAS gives support for data access, data management, data analysis, and data presentation.

SAS helps you to perform many analyses on your PCs

Now SAS is the most widely used statistical software .

SAS stand for “Statistical Analysis System” and it pronounced as “sass”, not spelled out as three letters.

Originally it intended for management and analysis of agricultural field experiments

A SAS program is made up of programming statements which SAS interprets to do the above functions.
What is Sas Usage?
•Started in late 1970s
•Used extensively at academic and business environments (medical device and pharmaceutical companies)
•Most analyses of publications in medical journals use SAS

A SAS Program consists of a series of SAS statements which are used to define, read in, manipulate, and analyze data. The typical SAS program is organized into three parts:

Data Definition and Options
Define the data location and the environment.

Data Step
Read, modify, subset, and write the data

Procedure(s)
Perform an action on the data
e.g. sort the data, compute means, run a regression, etc.

Basic Structure of SAS
There are two main components to most SAS programs

Data step(s)

Procedure step(s).

DataStep

The data step reads data from external sources, manipulates and combines it with other data set and prints reports.

The data step is used to prepare your data for use by one of the procedures (often called “procs”).

SAS is very lenient about the format of its input - statements can be broken up across lines, multiple statements can appear on a single line, and blank spaces and lines can be added to make the program more readable.
Data Step: Basics Each data step begins with the word data and optionally one or more data set names (and associated options) followed by a semicolon. The name(s) given on the data step are the names of data sets which will be created within the data step.
If you don’t include any names on the data step, SAS will create default data set names of the form datan, where n is an integer which starts at 1 and is incremented so that each data set created has a unique name within the current session. Since it becomes difficult to keep track of the default names, it is recommended that you always explicitly specify a data set name on the data statement.
When you are running a data step to simply generate a report, and don’t need to create a data set, you can use the special data set name _null_ to eliminate the output of observations.

Data Step: Inputting Data The input statement of SAS is used to read data from an external source, or from lines contained in your SAS program.
The infile statement names an external ﬁle or ﬁleref∗ from which to read the data; otherwise the cards; or datalines; statement is used to precede the data.

data one;
infile "input.data";
input a b c;
run;
Reading data from an external ﬁle
data one;
input a b c;
datalines;
. . .
;
Reading from inline data By default, each invocation of the input statement reads another record. This example uses free-form input, with at least one space between values.
∗A ﬁleref is a SAS name, created by the filename statement, which refers to an external ﬁle or other device

Data Step: input Statement There are three basic forms of the input statement:

List input (free form)
data fields must be separated by at least one blank. List the names of the variables, follow the name with a dollar sign ($) for character data.

Column input
It follow the variable name (and $ for character) with startingcolumn – endingcolumn.

Formatted input
Optionally precede the variable name with @startingcolumn; follow the variable name with a SAS format designation. (Examples of formats: $10. (10 column character), 6. (6 column numeric)) When mixing different input styles, note that for column and formatted input, the next input directive reads from the column immediately after the previous value, while for list input, the next directive reads from the second column after the previous value.

Procedure Step

The procedure steps perform analysis on the data, and produce (often huge amounts of) output.

The most effective strategy for learning SAS is to concentrate on the details of the data step, and learn the details of each procedure as you have a need for them.
Summary of DATA STEP

Reads in and processes your raw data and makes a SAS dataset.

Summary of Procedures (PROC STEP)

Performs specific statistical analyses

Some procedures are utility procedures such as PROC SORT that is used to sort your data

Accessing SAS
There are four ways to access SAS on a UNIX system:

Type sas
This opens the SAS “display manager”, which consists of three windows (program, log, and output). Some procedures must be run from the display manager.

Type sas -nodms
You will be prompted for each SAS statement, and output will scroll by on the screen.

Type sas -stdio SAS will act like a standard UNIX program, expecting input from standard input, sending the log to standard error, and the output to standard output;

Type sas filename.sas This is the batch mode of SAS - your program is read from filename.sas, the log goes to filename.log and the output goes to filename.lst.

Raw Data

Read in Data

Process Data
(Create new variables)

Output Data
(Create SAS Dataset)

-->Data Step

Analyze Data Using
Statistical Procedures

--->PROCs

Structure of Data

Made up of rows and columns

Rows in SAS are called observations

Columns in SAS are called variables

Together they make up the dataset (table)

An observation (row) is all the information for one entity (patient, patient visit, clinical center, county)

SAS processes data one observation at a time

Example of Data
12 observations (rows) and 5 variables (columns)

F 23 S 15 MN
F 21 S 15 WI
F 22 S 09 MN
F 35 M 02 MN
F 22 M 13 MN
F 25 S 13 WI
M 20 S 13 MN
M 26 M 15 WI
M 27 S 05 MN
M 23 S 14 IA
M 21 S 14 MN
M 29 M 15 MN

Types of Variables In SAS

Numeric (e.g. age, blood pressure) -- 54, 140

Character (patient ID, diagnosis) -- A001, TIA, 0410

When bringing data into SAS you need to tell SAS if the data is character. The default is numeric

Rules for SAS Statements

SAS statements end with a semicolon (;)

SAS variable names must be 32 characters or less, constructed of letters, digits and the underscore character. (Before version 7, the limit was 8.)

SAS is not case sensitive, except inside of quoted strings. Starting in Version 7, SAS will remember the case of variable names when it displays them.

Missing values are handled consistently in SAS, and are represented by a period (.).

It’s a good idea not to start variable names with an underscore, because special system variables are named that way.

Data set names follow similar rules as variables, but they have a different name space.
Example

DATA demo;
INFILE DATALINES;
INPUT gender $ age;

SAS statements can be entered in lower or uppercase
Example For Lower Case Declaration
data demo;
infile datalines;
input gender $ age;
Example For Upper Case Declaration
DATA DEMO;
INFILE DATALINES;
INPUT GENDER $ AGE;
Multiple SAS statements can appear on one line

Example

DATA demo; INFILE DATALINES; INPUT gender $ age; X1 = 0; X2 = 0; X3 = 0; X4 = 0;

A SAS statement can use multiple lines

INPUT gender $ age marstat;

Variable names can be from 1-32 characters and must begin with A-Z or an underscore (_). No special characters except underscore is allowed.

SYNTAX IS CORRECT FOR FOLLOWING VARIABLE NAMES

dbp12

DiastolicBloodPressure

_dbp12

SYNTAX IS INCORRECT FOR FOLLOWING VARIABLE NAMES

12dbp

dbp 12

dbp-12

DATA demo;
INFILE DATALINES;
INPUT gender $ age marstat $ credits state $ ;

if credits > 12 then fulltime = 'Y'; else fulltime = 'N'; if state = 'MN' then resid = 'Y'; else resid = 'N';
Datalines;

F 23 S 15 MN
F 21 S 15 WI
F 22 S 09 MN
F 35 M 02 MN
F 22 M 13 MN
F 25 S 13 WI
M 20 S 13 MN
M 26 M 15 WI
M 27 S 05 MN
M 23 S 14 IA
M 21 S 14 MN
M 29 M 15 MN

;
Run ;

PROC PRINT DATA=demo ; VAR gender age marstat credits fulltime state ; RUN; PROC MEANS DATA =demo; PROC FREQ DATA=demo;

DATA demo;
Create a SAS dataset called demo

INFILE DATALINES;
Where is the data?

INPUT gender $
age
marstat $
credits
state $ ;

What are the variable names and types?

if credits > 12 then fulltime = 'Y'; else fulltime = 'N';

if state = 'MN' then resid = 'Y'; else resid = 'N';
Statements 4 and 5 create 2 new variables

DATALINES;
Tells SAS the data is coming

F 23 S 15 MN
F 21 S 15 WI
F 22 S 09 MN
F 35 M 02 MN
F 22 M 13 MN
F 25 S 13 WI
M 20 S 13 MN
M 26 M 15 WI
M 27 S 05 MN
M 23 S 14 IA
M 21 S 14 MN
M 29 M 15 MN
;
Tells SAS the data is ended

RUN;
Tells SAS to run the statements above

PROC PRINT DATA=demo ;

VAR gender age marstat credits fulltime state ;

RUN;
Tells SAS to display the listed variables

Main SAS Windows (PC)

Editor Window

This window allows you to write your SAS programs and submit your programs by clicking on run icon to execute.

Log Window

This window displays the notes of SAS sessions, and tells you any errors, warnings after you submit your SAS programs.

Always look at the log window !

Tells how SAS understood your program

Output Window

gives the output generated from the PROCs
Results Window

index to all of your output

Messages in SAS Log
Errors

fatal in that program will abort

Warnings

messages that are usually important
Notes

messages that may or may not be important

Notes and warnings will not abort your program

* This is a short example program to demonstrate what a SAS program looks like. This is a comment statement because it begins with a * and ends with a semi-colon ;

F 23 S 15 MN
F 21 S 15 WI
F 22 S 09 MN
F 35 M 02 MN
F 22 M 13 MN
F 25 S 13 WI
M 20 S 13 MN
M 26 M 15 WI
M 27 S 05 MN
M 23 S 14 IA
M 21 S 14 MN
M 29 M 15 MN

;
Run ; TITLE 'Running the Example Program';

PROC PRINT DATA=demo ; VAR gender age marstat credits fulltime state ; RUN;

LOG WINDOW (or file)

NOTE: Copyright (c) 1999-2001 by SAS Institute Inc., Cary, NC, USA.
NOTE: SAS (r) Proprietary Software Release 8.2 (TS2M0) Licensed to UNIVERSITY OF MINNESOTA, Site 0009012001.
NOTE: This session is executing on the WIN_NT platform.
NOTE: SAS initialization used:
real time 7.51 seconds
cpu time 0.89 seconds

1 * This is a short example program to demonstrate what a
2 SAS program looks like. This is a comment statement because
3 it begins with a * and ends with a semi-colon ;
4
5 DATA demo; 6 INFILE DATALINES;
7 INPUT gender $ age marstat $ credits state $ ;
8
9 if credits > 12 then fulltime = 'Y'; else fulltime = 'N'; 10 if state = 'MN' then resid = 'Y'; else resid = 'N'; 11 Datalines; NOTE: The data set WORK.DEMO has 12 observations and 7 variables.

NOTE: DATA statement used:
real time 0.38 seconds
cpu time 0.06 seconds
25 RUN;
26 TITLE 'Running the Example Program';
27 PROC PRINT DATA=demo ;
28 VAR gender age marstat credits fulltime state ;
29 RUN;
NOTE: There were 12 observations read from the data set WORK.DEMO.
NOTE: PROCEDURE PRINT used:
real time 0.19 seconds
cpu time 0.02 seconds
30 PROC MEANS DATA=demo N SUM MEAN;
31 VAR age credits ;
32 RUN;
NOTE: There were 12 observations read from the data set WORK.DEMO.
NOTE: PROCEDURE MEANS used:
real time 0.25 seconds

cpu time 0.03 seconds

33 PROC FREQ DATA=demo; TABLES gender;
34 RUN;

NOTE: There were 12 observations read from the data set WORK.DEMO.
NOTE: PROCEDURE FREQ used:
real time 0.15 seconds
cpu time 0.03 seconds

sas

Thursday, 16 May 2013

Learning SAS From Free Best Websites And Materials

Monday, 6 May 2013

Introduction To Sas Basics

-->Data Step

--->PROCs

Rules for SAS Statements

Example

Create a SAS dataset called demo

Where is the data?

What are the variable names and types?

Tells SAS the data is coming

Tells SAS the data is ended

Tells SAS to run the statements above

Tells SAS to display the listed variables

Main SAS Windows (PC)