The following example shows how you can use PROC SURVEYFREQ to analyze sample survey data. The example uses data from a customer satisfaction survey for a student information system (SIS), which is a software product that provides modules for student registration, class scheduling, attendance, grade reporting, and other functions.
The software company conducted a survey of school personnel who use the SIS. A probability sample of SIS users was selected from the study population, which included SIS users at middle schools and high schools in the threestate area of Georgia, South Carolina, and North Carolina. The sample design for this survey was a twostage stratified design. A firststage sample of schools was selected from the list of schools in the threestate area that use the SIS. The list of schools (the firststage sampling frame) was stratified by state and by customer status (whether the school was a new user of the system or a renewal user). Within the firststage strata, schools were selected with probability proportional to size and with replacement, where the size measure was school enrollment. From each sample school, five staff members were randomly selected to complete the SIS satisfaction questionnaire. These staff members included three teachers and two administrators or guidance department members.
The SAS data set SIS_Survey contains the survey results, as well as the sample design information needed to analyze the data. This data set includes an observation for each school staff member responding to the survey. The variable Response contains the staff member’s response about overall satisfaction with the system.
The variable State contains the school’s state, and the variable NewUser contains the school’s customer status ('New Customer' or 'Renewal Customer'). These two variables determine the firststage strata from which schools were selected. The variable School contains the school identification code and identifies the firststage sampling units (clusters). The variable SamplingWeight contains the overall sampling weight for each respondent. Overall sampling weights were computed from the selection probabilities at each stage of sampling and were adjusted for nonresponse.
Other variables in the data set SIS_Survey include SchoolType and Department. The variable SchoolType identifies the school as a high school or a middle school. The variable Department identifies the staff member as a teacher, or an administrator or guidance department member.
The following PROC SURVEYFREQ statements request a oneway frequency table for the variable Response:
title 'Student Information System Survey'; proc surveyfreq data=SIS_Survey; tables Response; strata State NewUser; cluster School; weight SamplingWeight; run;
The PROC SURVEYFREQ statement invokes the procedure and identifies the input data set to be analyzed. The TABLES statement requests a oneway frequency table for the variable Response. The table request syntax for PROC SURVEYFREQ is very similar to the table request syntax for PROC FREQ. This example shows a request for a single oneway table, but you can also request twoway tables and multiway tables. As in PROC FREQ, you can request more than one table in the same TABLES statement, and you can use multiple TABLES statements in the same invocation of the procedure.
The STRATA, CLUSTER, and WEIGHT statements provide sample design information for the procedure, so that the analysis is done according to the sample design used for the survey, and the estimates apply to the study population. The STRATA statement names the variables State and NewUser, which identify the firststage strata. Note that the design for this example also includes stratification at the second stage of selection (by type of school personnel), but you specify only the firststage strata for PROC SURVEYFREQ. The CLUSTER statement names the variable School, which identifies the clusters (primary sampling units). The WEIGHT statement names the sampling weight variable.
Figure 86.1 and Figure 86.2 display the output produced by PROC SURVEYFREQ, which includes the "Data Summary" table and the oneway table, "Table of Response." The "Data Summary" table is produced by default unless you specify the NOSUMMARY option. This table shows there are 6 strata, 370 clusters or schools, and 1850 observations (respondents) in the SIS_Survey data set. The sum of the sampling weights is approximately 39,000, which estimates the total number of school personnel in the study area that use the SIS.
Student Information System Survey 
Data Summary  

Number of Strata  6 
Number of Clusters  370 
Number of Observations  1850 
Sum of Weights  38899.6482 
Figure 86.2 displays the oneway table of Response, which provides estimates of the population total (weighted frequency) and the population percentage for each category (level) of the variable Response. The response level 'Very Unsatisfied' has a frequency of 304, which means that 304 sample respondents fall into this category. It is estimated that 17.17% of all school personnel in the study population fall into this category, and the standard error of this estimate is 1.29%. Note that the estimates apply to the population of all SIS users in the study area, as opposed to describing only the sample of 1850 respondents. The estimate of the total number of school personnel that are 'Very Unsatisfied' is 6,678, with a standard deviation of 502. The standard errors computed by PROC SURVEYFREQ are based on the multistage stratified design of the survey. This differs from some of the traditional analysis procedures, which assume the design is simple random sampling from an infinite population.
Table of Response  

Response  Frequency  Weighted Frequency 
Std Dev of Wgt Freq 
Percent  Std Err of Percent 
Very Unsatisfied  304  6678  501.61039  17.1676  1.2872 
Unsatisfied  326  6907  495.94101  17.7564  1.2712 
Neutral  581  12291  617.20147  31.5965  1.5795 
Satisfied  455  9309  572.27868  23.9311  1.4761 
Very Satisfied  184  3714  370.66577  9.5483  0.9523 
Total  1850  38900  129.85268  100.000 
The following PROC SURVEYFREQ statements request confidence limits for the percentages, a chisquare goodnessoffit test, and a weighted frequency plot for the oneway table of Response. The ODS GRAPHICS ON statement enables ODS Graphics.
title 'Student Information System Survey'; ods graphics on; proc surveyfreq data=SIS_Survey nosummary; tables Response / clwt nopct chisq plots=WtFreqPlot; strata State NewUser; cluster School; weight SamplingWeight; run; ods graphics off;
The NOSUMMARY option in the PROC statement suppresses the "Data Summary" table. In the TABLES statement, the CLWT option requests confidence limits for the weighted frequencies (totals). The NOPCT option suppresses display of the weighted frequencies and their standard deviations. The CHISQ option requests a RaoScott chisquare goodnessoffit test, and the PLOTS= option requests a weighted frequency plot. ODS Graphics must be enabled before producing plots.
Figure 86.3 shows the oneway table of Response, which includes confidence limits for the weighted frequencies. The 95% confidence limits for the total number of users that are 'Very Unsatisfied' are 5692 and 7665. To change the level of the confidence limits, which equals 5% by default, you can use the ALPHA= option. Like the other estimates and standard errors produced by PROC SURVEYFREQ, these confidence limit computations take into account the complex survey design and apply to the entire study population.
Figure 86.4 displays the weighted frequency plot of Response. The plot displays weighted frequencies (totals) together with their confidence limits in the form of a vertical bar chart. You can use the PLOTS= option to request a dot plot instead of a bar chart or to plot percentages instead of weighted frequencies.
Student Information System Survey 
Table of Response  

Response  Frequency  Weighted Frequency 
Std Dev of Wgt Freq 
95% Confidence Limits for Wgt Freq 

Very Unsatisfied  304  6678  501.61039  5692  7665 
Unsatisfied  326  6907  495.94101  5932  7882 
Neutral  581  12291  617.20147  11077  13505 
Satisfied  455  9309  572.27868  8184  10435 
Very Satisfied  184  3714  370.66577  2985  4443 
Total  1850  38900  129.85268  38644  39155 
Figure 86.5 shows the chisquare goodnessoffit results for the table of Response. The null hypothesis for this test is equal proportions for the levels of the oneway table. (To test a null hypothesis of specified proportions instead of equal proportions, you can use the TESTP= option to specify null hypothesis proportions.)
The chisquare test provided by the CHISQ option is the RaoScott designadjusted chisquare test, which takes the sample design into account and provides inferences for the study population. To produce the RaoScott chisquare statistic, PROC SURVEYFREQ first computes the usual Pearson chisquare statistic based on the weighted frequencies, and then adjusts this value with a design correction. An F approximation is also provided. For the table of Response, the F value is 30.0972 with a pvalue of <0.0001, which indicates rejection of the null hypothesis of equal proportions for all response levels.
RaoScott ChiSquare Test  

Pearson ChiSquare  251.8105 
Design Correction  2.0916 
RaoScott ChiSquare  120.3889 
DF  4 
Pr > ChiSq  <.0001 
F Value  30.0972 
Num DF  4 
Den DF  1456 
Pr > F  <.0001 
Sample Size = 1850 
Continuing to analyze the SIS_Survey data, the following PROC SURVEYFREQ statements request a twoway table of SchoolType by Response:
title 'Student Information System Survey'; ods graphics on; proc surveyfreq data=SIS_Survey nosummary; tables SchoolType * Response / plots=wtfreqplot(type=dot scale=percent); strata State NewUser; cluster School; weight SamplingWeight; run; ods graphics off;
The STRATA, CLUSTER, and WEIGHT statements do not change from the oneway table analysis, because the sample design and the input data set are the same. These SURVEYFREQ statements request a different table but specify the same sample design information.
The ODS GRAPHICS ON statement enables ODS Graphics. The PLOTS= option in the TABLES statement requests a plot of SchoolType by Response, and the TYPE=DOT plotoption specifies a dot plot instead of the default bar chart. The SCALE=PERCENT plotoption requests a plot of percentages instead of totals.
Figure 86.6 shows the twoway table produced for SchoolType by Response. The first variable named in the twoway table request, SchoolType, is referred to as the row variable, and the second variable, Response, is referred to as the column variable. Twoway tables display all column variable levels for each row variable level. This twoway table lists all levels of the column variable Response for each level of the row variable SchoolType, 'Middle School' and 'High School'. Also SchoolType = 'Total' shows the distribution of Response overall for both types of schools. And Response = 'Total' provides totals over all levels of response, for each type of school and overall. To suppress these totals, you can specify the NOTOTAL option.
Student Information System Survey 
Table of SchoolType by Response  

SchoolType  Response  Frequency  Weighted Frequency 
Std Dev of Wgt Freq 
Percent  Std Err of Percent 
Middle School  Very Unsatisfied  116  2496  351.43834  6.4155  0.9030 
Unsatisfied  109  2389  321.97957  6.1427  0.8283  
Neutral  234  4856  504.20553  12.4847  1.2953  
Satisfied  197  4064  443.71188  10.4467  1.1417  
Very Satisfied  94  1952  302.17144  5.0193  0.7758  
Total  750  15758  1000  40.5089  2.5691  
High School  Very Unsatisfied  188  4183  431.30589  10.7521  1.1076 
Unsatisfied  217  4518  446.31768  11.6137  1.1439  
Neutral  347  7434  574.17175  19.1119  1.4726  
Satisfied  258  5245  498.03221  13.4845  1.2823  
Very Satisfied  90  1762  255.67158  4.5290  0.6579  
Total  1100  23142  1003  59.4911  2.5691  
Total  Very Unsatisfied  304  6678  501.61039  17.1676  1.2872 
Unsatisfied  326  6907  495.94101  17.7564  1.2712  
Neutral  581  12291  617.20147  31.5965  1.5795  
Satisfied  455  9309  572.27868  23.9311  1.4761  
Very Satisfied  184  3714  370.66577  9.5483  0.9523  
Total  1850  38900  129.85268  100.000 
Figure 86.7 displays the weighted frequency dot plot that PROC SURVEYFREQ produces for the table of SchoolType by Response. You can plot percentages instead of weighted frequencies by specifying the SCALE=PERCENT plotoption. You can use other plotoptions to change the orientation of the plot or to request a different twoway layout.
By default, without any other TABLES statement options, a twoway table displays the frequency, the weighted frequency and its standard deviation, and the percentage and its standard error for each table cell (combination of row and column variable levels). But there are several options available to customize your table display by adding more information or by suppressing some of the default information.
The following PROC SURVEYFREQ statements request a twoway table of SchoolType by Response that displays row percentages, and also request a chisquare test of association between the two variables:
title 'Student Information System Survey'; proc surveyfreq data=SIS_Survey nosummary; tables SchoolType * Response / row nowt chisq; strata State NewUser; cluster School; weight SamplingWeight; run;
The ROW option in the TABLES statement requests row percentages, which give the distribution of Response within each level of the row variable SchoolType. The NOWT option suppresses display of the weighted frequencies and their standard deviations. The CHISQ option requests a RaoScott chisquare test of association between SchoolType and Response.
Figure 86.8 displays the twoway table of SchoolType by Response. For middle schools, it is estimated that 25.79% of school personnel are satisfied with the student information system and 12.39% are very satisfied. For high schools, these estimates are 22.67% and 7.61%, respectively.
Figure 86.9 displays the chisquare test results. The RaoScott chisquare statistic equals 9.04, and the corresponding F value is 2.26 with a pvalue of 0.0605. This indicates an association between school type (middle school or high school) and satisfaction with the student information system at the 10% significance level.
Student Information System Survey 
Table of SchoolType by Response  

SchoolType  Response  Frequency  Percent  Std Err of Percent 
Row Percent 
Std Err of Row Percent 
Middle School  Very Unsatisfied  116  6.4155  0.9030  15.8373  1.9920 
Unsatisfied  109  6.1427  0.8283  15.1638  1.8140  
Neutral  234  12.4847  1.2953  30.8196  2.5173  
Satisfied  197  10.4467  1.1417  25.7886  2.2947  
Very Satisfied  94  5.0193  0.7758  12.3907  1.7449  
Total  750  40.5089  2.5691  100.000  
High School  Very Unsatisfied  188  10.7521  1.1076  18.0735  1.6881 
Unsatisfied  217  11.6137  1.1439  19.5218  1.7280  
Neutral  347  19.1119  1.4726  32.1255  2.0490  
Satisfied  258  13.4845  1.2823  22.6663  1.9240  
Very Satisfied  90  4.5290  0.6579  7.6128  1.0557  
Total  1100  59.4911  2.5691  100.000  
Total  Very Unsatisfied  304  17.1676  1.2872  
Unsatisfied  326  17.7564  1.2712  
Neutral  581  31.5965  1.5795  
Satisfied  455  23.9311  1.4761  
Very Satisfied  184  9.5483  0.9523  
Total  1850  100.000 
RaoScott ChiSquare Test  

Pearson ChiSquare  18.7829 
Design Correction  2.0766 
RaoScott ChiSquare  9.0450 
DF  4 
Pr > ChiSq  0.0600 
F Value  2.2613 
Num DF  4 
Den DF  1456 
Pr > F  0.0605 
Sample Size = 1850 