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Where to find this presentation and data  Short Courses  “Data Analysis in SAS”  Course Materials  Download Data to Desktop.

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Presentation on theme: "Where to find this presentation and data  Short Courses  “Data Analysis in SAS”  Course Materials  Download Data to Desktop."— Presentation transcript:

1 Where to find this presentation and data  Short Courses  “Data Analysis in SAS”  Course Materials  Download Data to Desktop Please log into Windows System! 1 Welcome to Data Analysis in SAS class !

2 Zhe Bao Dept. of Statistics & Dept. of Biological Sciences Data Analysis in SAS December 02, 2014 * Credit to Mark Seiss and Matthew Lanham for materials of this presentation

3 Laboratory for Interdisciplinary Statistical Analysis Collaboration: Visit our website to request personalized statistical advice and assistance with: Designing Experiments Analyzing Data Interpreting Results Grant Proposals Software (R, SAS, JMP, Minitab...) LISA statistical collaborators aim to explain concepts in ways useful for your research. Great advice right now: Meet with LISA before collecting your data. All services are FREE for VT researchers. We assist with research—not class projects or homework. LISA helps VT researchers benefit from the use of Statistics LISA also offers: Educational Short Courses: Designed to help graduate students apply statistics in their research Walk-In Consulting: Available Monday-Friday from 1-3 PM in the Old Security Building (OSB) for questions <30 mins. See our website for additional times and locations.

4 Why SAS? SAS versus R SAS will require a license ($), R is open-source Any statistical analysis you can do in SAS, you could probably do in R SAS is commercial software so additions take longer. R has new libraries being added frequently (but some would be unreliable). SAS help and documentation is professional. R documentation is lean. SAS handles large data sets with ease. R stores everything in RAM making it vulnerable. SAS and R are fairly easy to learn, but R feels more like natural language programming. Popularity Tiobe Sofware which ranks software popularity currently has SAS ranked #22 and R #24. KDNuggets 2013 software poll for data science or big data: R (37%), SAS (11%), MATLAB (10%) Rblogger.com - Number of Jobs on Indeed.com requesting skills in analytics: #1 SAS (12,272), #2 SPSS (3,289), #3 R (1,693) SAS and R comparison code

5 Presentation Outline 1.Introduction to the SAS Environment 2.Data Manipulation 3.Summary Procedures 4.Basic Statistical Analysis Procedures Linear regression and ANOVA Logistic regression

6 Reference Material The Little SAS Book – Delwiche and Slaughter SAS Programming I: Essentials SAS Programming II: Data Manipulation Techniques (by SAS) Presentation and Data

7 Presentation Outline Questions/Comments Individual Goals/Interests

8 Part I: Introduction to the SAS Environment 1.SAS Programs 2.SAS Data Sets and Data Libraries 3.SAS System Help 4.Creating SAS Data Sets

9 SAS Environment When you begin SAS, you should see 3 windows by default: Log window Output Window Editor Window

10 SAS Environment 1. Explorer window – allows you to view and manage your SAS files 2. Results window – helps you navigate and manage output from programs submitted. Uses a tree structure to list various types of output. On the left hand side is where you will find:

11 SAS Programs Editor Window File extension -.sas SAS program – sequence of steps that the user submits for execution Editor window has four uses: Access and edit existing SAS programs Write new SAS programs Submitting SAS programs for execution Saving SAS programs Submitting SAS programs Entire program; Selection of the program Keyboard shortcuts Tips: change preference, add number to line

12 SAS Programs Syntax Rules for SAS statements Free-format – can use upper or lower case Usually begin with an identifying keyword (data, proc, by etc.) Always end with a semicolon “;” Can span multiple lines Multiple statements can be on the same line Add comments to make the program easier to read * or /* */ Errors Misspelled key words or file name Missing or invalid punctuation (missing semi-colon common) Invalid options Indicated in the Log window

13 SAS Programs Two Basic steps in SAS programs: Data Steps Typically used to create SAS datasets and manipulate data, Begins with DATA statement Proc Steps Typically used to process SAS data sets and carry out statistical analysis Begins with PROC statement The end of the DATA or PROC steps are indicated by: RUN statement – most steps QUIT statement – some steps Beginning of another step (DATA or PROC statement)

14 SAS Programs Output generated from SAS program – 2 Windows SAS log Information about the processing of the SAS program Includes any warnings or error messages Accumulated in the order the data and procedure steps are submitted SAS output Reports generated by the SAS procedures Accumulates output in the order it is generated Clean the log window: DM “log;clear;”;

15 SAS Data Sets and Data Libraries SAS Data Set Specifically structured file that contains data values. File extension -.sas7bdat Rows and Columns format – similar to Excel Columns – variables in the table corresponding to fields of data Rows – single record or observation Two types of variables Character – contain any value (letters, numbers, symbols, etc.) Numeric – floating point numbers (including dates and times) (More on variable attributes: documentation/cdl/en/lrcon/62955/HTML/default/viewer.htm#a htm) Located in SAS Data Libraries

16 SAS Data Sets and Data Libraries SAS Data Libraries Contain SAS data sets Identified by assigning a library reference name – libref Temporary Work library SAS data files are deleted when session ends Library reference name not necessary Permanent SAS data sets are saved after session ends SASUSER library You can create and access your own libraries

17 SAS Data Sets and Data Libraries SAS Data Libraries (cont.) Assigning library references Syntax LIBNAME libref ‘SAS-data-library’; Rules for Library References 8 characters or less Must begin with letter or underscore Other characters are letters, numbers, or under scores

18 SAS Data Sets and Data Libraries SAS Data Libraries (cont.) Identifying SAS data sets within SAS Data Libraries libref.filename Accessing SAS data sets within SAS Data Libraries Example:DATA new_data_set; set libref.filename; run; Creating SAS data sets within SAS Data Libraries Example:DATA libref.filename_new; set old_data_set; run; If we closed our SAS session now what do you think would happen?

19 SAS System Help SAS Help and Documentation Help  SAS Help and Documentation Icon SAS Online Help

20 Creating SAS Data Sets Creating a SAS data sets from raw data Three common methods: 1. Importing existing data sets using the Import wizard 2. Importing existing raw data in SAS program using proc import 3. Manually entering raw data in SAS program using data step DATA data=libref.filename; INPUT ; DATALINES; ;

21 Creating SAS Data Sets Using the import data menu option 1.File  Import Data 2.Standard data source  select the file format 3.Specify file location or Browse to select file 4.Create name for the new SAS data set and specify location 5. Click “Finish” 6. Review the log for errors 7. Review the data file

22 Creating SAS Data Sets Compatible file formats Microsoft Excel Spreadsheets Microsoft Access Databases Comma Separate Files (.csv) Tab Delimited Files (.txt) dBASE Files (.dbf) JMP data sets SPSS Files Lotus Spreadsheets Stata Files Paradox Files ……

23 Creating SAS Data Sets Assignment Import State_SAT_data.xls  Assign as work.state_sat_data.sas7bdat Import State_region_data.txt  Assign as work.state_region_data.sas7bdat

24 Creating SAS Data Sets Example Data Sets 1) Excel File – State_SAT_data.xls Extracted from 1997 Digest of Education Statistics, an annual publication of the U.S. Department of Education Contains variables that show the relationship between public school expenditure and SAT performance Variables: –State (state) –Current expenditure per pupil (expend) –Average pupil to teacher ratio (PT_ratio) –Estimated annual salary of teachers (salary) –Percentage of eligible students taking the SAT (students) –Average verbal SAT score (verbal) –Average math SAT Score (math) –Average total score (total)

25 Creating SAS Data Sets Example Data Sets (Cont.) 2) Text file – State_region_data.txt Contains region assignments for each state 1 = New England 2 = Middle Atlantic 3 = East North Central 4 = West North Central 5 = South Atlantic 6 = East South Central 7 = West South Central 8 = Mountain 9 = Pacific

26 Questions/Comments Part I: Introduction to the SAS Environment

27 Part II: Data Manipulation 1.Data Set Information 2.Data Set Manipulation Data Set Processing 3.Combining Data Sets A.Concatenating/Appending B.Merging 4.Saving Data Sets

28 Data Set Information Proc Contents Output a table of contents/structure of the specified data set Data Set Information Data set name Number of observations Number of Variables Variable Information Type (numeric or character) Length Formats Syntax: PROC CONTENTS DATA=libname.input_data_set ; RUN;

29 Data Set Information Assignment Obtain Data Set Information for work.state_sat_data and work.state_region_data You can try to add these useful options: position, short, out=filename noprint

30 Data Set Information Solution proc contents data=state_sat_data out=state_sat_contents noprint; run; proc contents data=state_region_data; run;

31 Data Set Manipulation Create a new SAS data set using an existing SAS data set as input with modifications Specify name of the new SAS data set after the DATA statement Use SET statement to identify SAS data set being read Syntax: DATA output_data_set; SET input_data_set; ; RUN; By default the SET statement reads all observations and variables from the input data set into the output data set. Create new variables or Change variable formats

32 Data Set Manipulation Assignment Statements Evaluate an expression Assign resulting value to a variable General Form:variable = expression; Example:miles_per_hour = distance/time; Note: make sure the order of variables in statements is correct! SAS Functions Perform arithmetic functions, compute simple statistics, manipulate dates, etc. General Form:variable=function_name(argument1, argument2,…); Example: Time_worked = sum(Day1,Day2, Day3, Day4, Day5); More useful functions:

33 Data Set Processing “DATA steps execute line by line and observation by observation.” DATA steps read in data from existing data sets or raw data files one row at a time, like a loop DATA step reads data from the input data set in the following way: 1. Read in current row from input data set to Program Data Vector (PDV) 2.Process SAS statements 3.PDV to output data set 4.Set current row to the next row in the input data set 5.Iterate to Step 1

34 Data Set Manipulation Selecting Variables Use DROP and KEEP to determine which variables are written to new SAS data set. 3 Ways DROP and KEEP as statements –Form:DROP Variable1 Variable2; KEEP Variable3 Variable4 Variable5; DROP and KEEP options in SET statement –Form:SET input_data_set (KEEP=Var1 Var2); DROP and KEEP options in data statement –Form:DATA output_data_set (KEEP=Var1 Var2); Notice the difference!

35 Data Set Manipulation Conditional Processing Uses IF-THEN-ELSE logic General Form:IF THEN ; ELSE IF THEN ; ELSE ; is a true/false statement, such as: Day1=Day2, Day1 > Day2, Day1 < Day2 Day1+Day2=10 Sum(day1,day2)=10 Day1=5 and/or Day2=5

36 Data Set Manipulation Conditional Processing SymbolicMnemonicExample =EQIF region=‘Spain’; ~= or ^=NEIF region ne ‘Spain’; >GTIF rainfall > 20; =GEIF rainfall ge 20; <=LEIF rainfall <= 20; &ANDIF rainfall ge 20 & temp < 90; | or !ORIF rainfall ge 20 OR temp < 90; IS NOT MISSING IF region IS NOT MISSING; BETWEEN AND IF region BETWEEN ‘Plain’ AND ‘Spain’; CONTAINSIF region CONTAINS ‘ain’; INIF region IN (‘Rain’, ‘Spain’, ‘Plain’);

37 Data Set Manipulation Conditional Processing (cont.) If is true, is processed ELSE IF and ELSE are only processed if is false Only one statement specified using this form Use DO and END statements to execute a group of statements General Form:IF THEN DO; ; END; ELSE DO; ; END;

38 Data Set Manipulation Subsetting Sample (Observations) We will look at two ways Using IF statement Using WHERE option in SET statement To select a random sample: PROC SURVEYSELECT IF statement Only writes observations to the new data set in which an expression is true; General Form: IF ; Example: IF career = ‘Teacher’; IF sex ne ‘M’; In the second example, only observations where sex is not equal to ‘M’ will be written to the output data set

39 Data Set Manipulation Subsetting Sample (Observations) WHERE Option in SET statement Use option to only read rows from the input data set in which the expression is true General Form:SET input_data_set (where=( )); Example:SET vacation (where=(destination=‘Bermuda’)); Only observations where the destination equals ‘Bermuda’ will be read from the input data set Comparison Resulting output data set is equivalent IF statement – all rows read from the input data set Where option – only rows where expression is true are read from input data set Difference in processing time when working with big data sets

40 Data Set Manipulation Assignments 1.Create new dataset work.state_SAT_data2 from work.state_SAT_data Assign new variable  upper_ind If total > 1000 then upper_ind=1 Otherwise upper_ind=0 2.Create new dataset work.south from work.state_region_data Specify work.south contains only records from regions 5, 6, or 7 Specify work.south only contains the state variable

41 Data Set Manipulation Solutions 1. data state_sat_data2; set state_sat_data; if total>1000 then upper_ind=1; else upper_ind=0; run;

42 Data Set Manipulation Solutions 2. data south; set state_region_data; if region=5 or region=6 or region=7; keep state; run; OR data south; set state_region_data(where=(region=5 or region=6 or region=7)); keep state; run;

43 Data Set Manipulation PROC SORT sorts data according to specified variables General Form:PROC SORT DATA=input_data_set ; BY Variable1 Variable2; RUN; Sorts data according to Variable1 and then Variable2; By default, SAS sorts data in ascending order Number low to high A to Z Use DESCENDING statement for numbers high to low and letters Z to A BY City DESCENDING Population; SAS sorts data first by city A to Z and then Population high to low

44 Data Set Manipulation Some Options NODUPKEY Eliminates observations that have the same values for the BY variables Delete duplicate observations (exact match for all variables): NODUPRECS OUT=output_data_set By default, PROC SORT replaces the input data set with the sorted data set Using this option, PROC SORT creates a newly sorted data set and the input data set remains unchanged

45 Combining Data Sets Concatenating (or Appending) Stacks each data set upon the other If one data set does not have a variable that the other datasets do, the variable in the new data set is set to missing (‘.’) for the observations from that data set. General Form:DATA output_data_set; SET data1 data2; run; PROC APPEND may also be used If the two data files have different variable names for the same thing, you can use RENAME in set statement. SET data1(RENAME=(var1=common_name)) data2(RENAME=(var2=common_name));

46 Combining Data Sets Merging Data Sets One-to-One Match Merge A single record in a data set corresponds to a single record in all other data sets Example: Patient and Billing Information One-to-Many Match Merge Matching one observation from one data set to multiple observations in other data sets Example: County and State Information Note:Data must be sorted before merging can be done (PROC SORT)

47 Combining Data Sets One-to-One Match Merge Usually need at least one common variable between data sets – matching purposes For the example, a patient ID would be needed Do not need common variable if all data sets are in exactly the same order General Form:DATA output_data_set; MERGE input_data_set1 input_data_set2; By variable1 variable2; RUN;

48 Combining Data Sets One-to-One Match Merge Example: PerformanceGoals Code: DATA work.compare; MERGE work.performance work.goals; BY month; difference=sales-goal; RUN; MonthSales MonthGoal

49 Combining Data Sets One-to-One Match Merge Example cont.: Compare MonthSalesGoalDifference

50 Combining Data Sets One-to-Many Match Merge Requires at least one common variable in the data sets for matching purposes For the example, State information is in both the state and county files If two data sets have variables with the same name, the variables in the second data set will overwrite the variable in the first. General Form:DATA output_data_set; MERGE Data1 Data2 Data3; BY Variable1 Variable2; RUN;

51 Combining Data Sets One-to-Many Match Merge Example: VideosAdjustment Code: DATA work.prices; MERGE work.videos work.adjustment BY category; NewPrice=(1-adjustment)*sales; RUN; CategorySales Aerobics12.99 Aerobics13.99 Aerobics13.99 Step12.99 Step12.99 Weights15.99 CategoryAdjustment Aerobics.20 Step.30 Weights.25

52 Combining Data Sets One-to-Many Match Merge Example cont.: Videos CategorySalesAdjustmentNewPrice Aerobics Aerobics Aerobics Step Step Weights

53 Combining Data Sets Assignment Create the dataset work.state_data Merge work.state_sat_data2 with work.state_region_data by the state variable

54 Combining Data Sets Solution proc sort data=state_sat_data2; by state; run; proc sort data=state_region_data; by state; run; data state_data; merge state_sat_data2 state_region_data; by state; run; *****Check: Has the state_data been created correctly?*****

55 Saving Data Sets Save as permanent SAS data set (.sas7bdat) DATA libref.filename; SET current_name; RUN; Save as other formats 1. PROC EXPORT data=current_name outfile=“C:\Users\student\Desktop\SAS” dbms=xlsx; RUN; 2. Export Wizard 1)File  Export Data 2)Specify SAS data set 3)Standard data source  select the file format 4)Specify File Folder and Filename

56 Combining Data Sets Assignment Save the dataset state_data on your desktop as.csv or.xlsx file

57 Questions/Comments Part II: Data Manipulation

58 Part III: Summary Procedures Print Procedure Plot Procedure Univariate Procedure Means Procedure Freq Procedure

59 Print Procedure PROC PRINT is used to print data to the output window By default, prints all observations and variables in the SAS data set General Form:PROC PRINT DATA=input_data_set ; RUN; Some Options input_data_set (obs=n) -Specifies the number of observations to be printed in the output NOOBS - Suppresses printing observation number LABEL - Prints the labels instead of variable names

60 Print Procedure Optional SAS statements BY variable1 variable2 variable3; Starts a new section of output for every new value of the BY variables ID variable1 variable2 variable3; Prints ID variables on the left hand side of the page and suppresses the printing of the observation numbers SUM variable1 variable2 variable3; Prints sum of listed variables at the bottom of the output VAR variable1 variable2 variable3; Prints only listed variables in the output

61 Print Procedure Assignment Use PROC PRINT to print out the state variable separately for each region Note: All procedures in this summary statistics section of course will be run on the data set work.state_data. ( If for some season your SAS shuts down/restarts, simply go ahead and import the permanent state_data file we just exported.)

62 Print Procedure Solution proc sort data=state_data; by region; run; proc print data=state_data; var state; by region; run;

63 Plot Procedure Used to create basic scatter plots of the data Use PROC GPLOT (with symbol statement) or PROC SGPLOT for more sophisticated plots; use PROC GCHART for bar chart and pie chart General Form: PROC PLOT DATA=input_data_set; PLOT vertical_variable * horizontal_variable/ ; RUN; By default, SAS uses letters to mark points on plots A for a single observation, B for two observations at the same point, etc. To specify a different character to represent a point PLOT vertical_variable * horizontal variable = ‘*’;

64 Plot Procedure To specify a third variable to use to mark points—detect how the relationship between Y and X different at different levels of a 3 rd variable PLOT vertical_variable * horizontal_variable = third_variable; To plot more than one variable on the vertical axis PLOT vertical_variable1 * horizontal_variable=‘2’ vertical_variable2 * horizontal_variable=‘1’/OVERLAY ;

65 Plot Procedure Assignment Use the PLOT PROCEDURE to plot SAT Verbal scores versus SAT Math Scores Use the value of the region variable to mark points (the third variable)

66 Plot Procedure Solution proc plot data=state_data; plot math*verbal=region; run; * Add regression line for the relationship between math score and verbal score? Use PROC GPLOT-- can be found in the code file

67 Univariate Procedure PROC UNIVARIATE is used to examine the distribution of data Produces distribution and summary statistics for a single variable Includes mean, median, mode, standard deviation, skewness, kurtosis, quantiles, etc. Used for detecting missing values and extreme observations General Form: PROC UNIVARIATE DATA=input_data_set ; VAR variable1 variable2 variable3; ; RUN ; If the variable statement is not used, summary statistics will be produced for all numeric variables in the input data set.

68 Univariate Procedure Options include: PLOT – produces Stem-and-leaf plot or Horizontal bar plot, Box plot, and Normal probability plot; NORMAL/NORMAL TEST– produces tests of Normality Statements include: HISTOGRAM Histogram var1 var2/normal midpoint= ctex=; ID—output id in the extreme observations table QQPLOT—test if variables follow certain distributions

69 Univariate Procedure Assignment Use PROC UNIVARIATE to produce a normal probability plot and test the normality of the SAT Total variable and Expenditure variable.

70 Univariate Procedure Solution proc univariate data=state_data normal plot; var expend total; run;

71 Means Procedure Similar to the Univariate procedure, produces summary statistics General Form:PROC MEANS DATA=input_data_set ; ; RUN; With no options or optional SAS statements, the Means procedure will print out the number of non-missing values, mean, standard deviation, minimum, and maximum for all numeric variables in the input data set for all the numerical variables

72 Means Procedure Options Statistics Available Note: The default alpha level for confidence limits is 95%. Use ALPHA= option to specify different alpha level. CLMTwo-Sided Confidence LimitsRANGERange CSSCorrected Sum of SquaresSKEWNESSSkewness CVCoefficient of VariationSTDDEVStandard Deviation KURTOSISKurtosisSTDERRStandard Error of Mean LCLMLower Confidence LimitSUMSum MAXMaximum ValueSUMWGTSum of Weight Variables MEANMeanUCLMUpper Confidence Limit MINMinimum ValueUSSUncorrected Sum of Squares NNumber Non-missing ValuesVARVariance NMISSNumber Missing ValuesPROBTProbability for Student’s t MEDIAN (or P50)MedianTStudent’s t Q1 (P25)25% QuantileQ3 (P75)75% Quantile P11% QuantileP55% Quantile P1010% QuantileP9090% Quantile P9595% QuantileP9999% Quantile

73 Means Procedure Optional SAS Statements VAR Variable1 Variable2; Specifies which numeric variables statistics will be produced for BY Variable1 Variable2; Calculates statistics for each combination of the BY variables Output out=output_data_set; Creates data set with the default statistics

74 Means Procedure Assignment Use PROC MEANS to calculate the mean and variance of the expend variable for each region

75 Means Procedure Solution proc sort data=state_data; by region; run; proc means data=state_data mean var; var expend; by region; run;

76 FREQ Procedure PROC FREQ is used to generate frequency tables Most common usage is create table showing the distribution of categorical variables General Form:PROC FREQ DATA=input_data_set; TABLE variable1*variable2*variable3/ ; RUN; Options LIST – prints cross tabulations in list format rather than grid MISSING – specifies that missing values should be included in the tabulations OUT=output_data_set – creates a data set containing frequencies, list format NOPRINT – suppress printing in the output window Use BY statement to get percentages within each category of a variable

77 FREQ Procedure Assignment Use PROC FREQ to find the number of states within each region

78 FREQ Procedure Solution proc freq data=state_data; table region; run;

79 Part III: Summary Procedures Questions/Comments

80 Part IV: Basic Statistical Analysis Procedures A. Linear Regression and ANOVA 1.Correlation – PROC CORR 2.Regression – PROC REG 3.Analysis of Variance – PROC ANOVA B. Categorical Data and Generalized Linear Model 1.Chi-square Test of Association – PROC FREQ 2.Generalized Linear Models – PROC GENMOD

81 CORR Procedure PROC CORR is used to calculate the correlations between variables Correlation coefficient measures the linear relationship between two variables Values Range from -1 to 1 Negative correlation - as one variable increases the other decreases Positive correlation – as one variable increases the other increases 0 – no linear relationship between the two variables 1 – perfect positive linear relationship -1 – perfect negative linear relationship General Form:PROC CORR DATA=input_data_set VAR Variable1 Variable2; With Variable3; RUN;

82 CORR Procedure PROC CORR (cont.) If the VAR and WITH statements are not used, correlation is computed for all pairs of numeric variables Options include SPEARMAN – computes Spearman’s rank correlations KENDALL – computes Kendall’s Tau coefficients Plot=matrix

83 CORR Procedure Assignment We will use a new data set: petrol2.sas7bdat First import this data set into one of your work library as “petrol”. Then use PROC CORR to find the correlation between all the variables. (optional: create the correlation plots for variable )

84 CORR Procedure Solution proc corr data=petrol; run; OR ods graphics on; title 'Petrol Consume Data'; proc corr data=petrol cov plots=matrix; var petroltax income highway_mile driver_pr consumpetrol; with petroltax income highway driver consumpetrol; run; ods graphics off;

85 REG Procedure PROC REG is used to fit linear regression models by least squares estimation One of many SAS procedures that can perform regression analysis (PROC GLM, PROC MIXED) Only continuous independent variables General Syntax: PROC REG DATA=input_data_set MODEL dependent=independent1 independent2/ ; ; RUN; PROC REG statement options include PCOMIT=m - performs principle component estimation with m principle components CORR – displays correlation matrix for independent variables in the model

86 REG Procedure MODEL statement options include SELECTION= Specifies a model selection procedure be conducted – FORWARD, BACKWARD, and STEPWISE ADJRSQ - Computes the Adjusted R-Square MSE – Computes the Mean Square Error VIF – Indicates multicollinearity CLB – computes confidence limits for parameter estimates ALPHA= Sets significance value for confidence and prediction intervals and tests

87 REG Procedure Optional statements include PLOT Dependent*Independent – generates plot of data

88 REG Procedure Assignment Use PROC REG to generate a multiple linear regression model Dependent Variable – consumpetrol: 1) Use all the other variables as independent variables 2) Use Stepwise Selection  stepwise selection

89 REG Procedure Solution 1) proc reg data=petrol corr; model consumpetrol = petroltax income highway driver /vif; run; 2) proc reg data=petrol; model consumpetrol = petroltax income highway driver/ selection=Stepwise slentry=0.5 slstay=0.1; quit;

90 ANOVA Procedure PROC ANOVA performs analysis of variance Designed for balanced data (PROC GLM used for unbalance data) Can handle nested and crossed effects and repeated measures General Form: PROC ANOVA DATA=input_data_set ; CLASS independent1 independent2; MODEL dependent=independent1 independent2; ; Run; Class statement must come before model statement, used to define classification variables

91 ANOVA Procedure Useful PROC ANOVA statement option – OUTSTAT=output_data_set Generates output data set that contains sums of squares, degrees of freedom, statistics, and p-values for each effect in the model Useful optional statement – MEANS independent1/ Used to perform multiple comparisons analysis Set to: TUKEY – Tukey’s studentized range test BON – Bonferroni t test T – pairwise t tests Duncan – Duncan’s multiple-range test Scheffe – Scheffe’s multiple comparison procedure

92 ANOVA Procedure Question:In state_data, 1) Are there significant differences between the Math SAT scores of students from different regions? 2) If there are significant differences, which regions are different? Assignment Use PROC ANOVA to determine if there are significant differences in the Math SAT variable between regions Perform multiple comparisons between regions using Tukey’s Adjustment

93 ANOVA Procedure Solution proc anova data=state_data; class region; model math=region; means region/tukey; run;

94 Assumptions of linear regression: (1) IID (“random”) samples (2) Equal variances Use unequal variance test (Satterthwaite) (3) Normally distributed Transformation; Could try non-parametric test Nonparametric methods relax underlying assumptions about how the data is generated, because maybe you don’t know or the parametric assumptions are not satisfied. Nonparametric equivalent to two-sample t-test is: Wilcox rank sum test (Wilcoxon-Mann-Whitney Test) PROC NPAR1WAY Assumptions for Linear Regression

95 Part IV Summary Procedures Questions/Comments? Part A: Linear regression and ANOVA

96 FREQ Procedure PROC FREQ can also be used to perform analysis with categorical data General Form:PROC FREQ DATA=input_data_set; TABLE variable1 variable2/ ; RUN; TABLE statement options include: AGREE – Tests and measures of classification agreement including McNemar’s test, Bowker’s test, Cochran’s Q test, and Kappa statistics CHISQ -- Chi-square test of homogeneity and measures of association MEASURE -- Measures of association include Pearson and Spearman correlation, gamma, Kendall’s Tau, Stuart’s tau, Somer’s D, lambda, odds ratios, risk ratios, and confidence intervals

97 GENMOD Procedure PROC GENMOD is used to estimate linear models in which the response is not necessarily continuous variable Logistic and Poisson regression are examples of generalized linear models General Form: PROC GENMOD DATA=input_data_set; CLASS independent1; MODEL dependent = independent1 independent2/ dist= link= ; run;

98 GENMOD Procedure DIST = - specifies the distribution of the response variable LINK= - specifies the link function from the linear predictor to the mean of the response Example – Logistic Regression DIST = binomial LINK = logit Example – Poisson Regression DIST = poisson LINK = log

99 GENMOD Procedure Assignment Use PROC GENMOD to perform Logistic Regression on the apple_juice data set Dependent variable – CRA7152 Independent variables pH ( ) Brix (i.e. Sugar content of an aqueous solution, 11-19) Temperature (25-50 °C) Nisin concentration (0-70) (variable name Nisin)

100 GENMOD Procedure Solution proc genmod data=apple_juice descending; model CRA7152=PH Brix Temperature Nisin/dist=bin link=logit; run;

101 Reference Material The Little SAS Book – Delwiche and Slaughter SAS Programming I: Essentials SAS Programming II: Data Manipulation Techniques (by SAS) SAS help file; support.sas.com Presentation and Data

102 Questions/Comments


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