§ 63.11 – How do I use a table of random numbers?

 

(a)    Suppose that:

(1)   you have 101 vanpools that you expect to operate every day of next week,

(2)   you have numbered the vanpool days for all vanpools as shown in Table 63.03, and

(3)   your sampling plan for your vanpool service requires 2 vanpool days per week. 

(b)   You must work with a constant length of digits from a table of random numbers for sampling.  This constant length is given by the number of digits in the longest serial number you have assigned to members of the list of all service units. 

(1)   This constant length would be 4 for the example in Table 63.03 because all serial numbers are four-digits long. 

(2)   This constant length would be 5 if your serial numbers vary in length, ranging from one to five digits.

(c)    You must combine adjacent digits from the table of random numbers as needed to obtain a two-, three-, or four-digit number, or any other length number from the table. 

(1)   You may choose to work with rows or columns in combining adjacent digits.  You may start with any row if you choose to work with rows.  You may start with any column if you choose to work with columns.  You may also choose to work from right to left or from left to right if you choose to work with rows. 

(2)   If you choose to work with rows and to start with row 1, for example, the first 9 four-digit numbers from Table 63.01 would be:

 

1048, 0480, 4801, 8015, 0150, 1501, 5011, 0110, and 1101.

 

(d)   You must continue forming four-digit numbers until you find two four-digit numbers from the table of random numbers that are in the summary table of serial numbers (Table 63.03).  In the above example, these two numbers are 1048 and 1101.  That is, you should select vanpools 48 and 101 and collect sample data from them on Monday of next week.

(e)    Once you are done sampling for a week, you should mark where you stopped forming four-digit numbers in the table of random numbers.  For example, the symbol, $, has been inserted between digits 1 and 5 in row 1 and column 3 of Table 63.01.  You should start the above process for a later week after that mark.

(f)    Once you are done sampling for a year, you should mark where you stopped forming four-digit numbers in the table of random numbers if you plan to use this method of random sampling in the future.  

(1)   If you number your service units exactly as for a previous sampling year, you should start the above process for a new sampling year after the last mark of your previous sampling year.

(2)   If you number your service units with a different approach for a new sampling year, you may start the above process anywhere in the table of random numbers.