Analysis of the Vehicle Inventory and Use Survey for Trucks ... - About

groups for each region, we would generate a frequency table based on the unexpanded sample data.
Example of SAS Code to Generate Table of Number of Sample Records in each Vehicle Group for Each Region
Proc freq data=Regions;
Table VG*REGION;
Run;
Means and Standard Deviation
In summarizing the general characteristics of a certain vehicle type in the truck population, the mean and standard
deviation are useful measures. There are two procedures in SAS for generating means: the Proc Means and the Proc
GLM procedures. In each procedure, the ‘Freq EXPANF’ statement is added in order to weight the sample data in
order to reflect the population. For example, if a record has 40,000 miles as its annual miles traveled and its
EXPANF=10, then this record states that 10 vehicles in the population have annual VMTs of 40,000 miles. Proc
Means is used for 1997 VIUS analysis
One should be aware that in both these procedures the ‘Freq EXPANF’ statement will only accept integer values. If
a real number is given, the procedure will only use the integer part of the number. EXPANF is a real number with
values out to the two decimal places. In our analysis, we did not want the EXPANF to be truncated, so we
multiplied the EXPANF for every record by 100, in order to shift the information in the two decimal places over into
the integer part of the number. Then we generated the means using this new EXPANF. In the results, the
population sizes associated with the means will be off by a factor of 100. Dividing the population sizes by 100 will
give the true sizes.
General Format for Proc Sort Before running the Proc Means procedure, the Proc Sort procedure may have to be
used to reorganize the data for analysis.
Proc Sort data=dataset name;
By Variable list;
Run;
General Format for Proc Means
Proc Means data=dataset name;
Var Variable list;
By Variable list;
Freq Variable;
Run;
Example of Proc Means procedure to Generate Mean VMT for Each Body Type Group
Proc Sort data=VIUS;
By BODTYP;
Proc Means data=VIUS;
Variable ANNMIL;
By BODTYP;
Freq EXPANF;
Run;
General Format for Proc GLM
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