|Indicators for monitoring national drug policies (WHO/EDM, 1999, 250 p.)|
The random number table on the following page has been taken from: Hill AB. A short textbook of medical statistics. London, Hodder and Stoughton, 1977.
1. First, decide how large a number you need. Next, count if it is a one, two or larger digit number. For example, if your sampling frame consists of 10 units, you must choose from numbers 1-10 (inclusive). You must use two digits to ensure that 10 has an equal chance of being included.
You also use two digits for a sampling frame consisting of 0-99 units.
If, however, your sampling frame has 0-999 units, then you obviously need to choose from three digits. In this case, you take an extra digit from the table to make up the required three digits. For example, the number in columns 10 and 11, row 27, i.e. 43, would become 431; going down, the next numbers would be 107, 365 etc.
You would do the same if you needed a four digit number for a sampling frame of 0-9999 units. In our example of the number in columns 10, 11 and 12, row 27, i.e. 431, this would now become 4316, the next down 1075, and so on.
2. Decide beforehand whether you are going to go across the page to the right, down the page, across the page to the left, or up the page.
3. Without looking at the table, pinpoint a number using a pencil, pen, stick, or even your finger.
4. If this number is within the range you need, take it. If not, continue to the next number in the direction you chose beforehand (across, up or down the page) until you find a number that is within the range you need.
For example, if you need a number between 0 and 50 and you began at columns 21 and 22, row 21, you get 74, which is obviously too big. So you could go down (having decided beforehand to go down) to 97, also too big, and then to 42, which is acceptable, and select it.