Understanding Rates
This topic explains sample and alternate rates and how they are used with random testing.
Sample Rate
The Drug and Alcohol Sample Rate fields record the total percentage of employees in the pool to sample in a given year. If, for example, you desire to sample 50% of the pool in a given year, and plan to make two selections during that year, 25% will be selected each time. But if there is to be only one selection in the entire year, 50% of the pool will be selected at that one sampling. The reverse is also true. If a company tells you that it wants to sample 10% each time and desires two samples per year, the Sample Rate will be 20%.
If you prefer to have the alcohol and drug samples drawn separately, run the randomization for the desired drug sample rate with the alcohol sample rate set to zero. Then run the randomization again, this time entering the desired alcohol sample rate with the drug sample rate set to zero. On the second randomization, you will be warned that the pool is not due, but you may still proceed.
You should realize that the pool size may not always be evenly divisible by the number of samples required, creating rounding-off issues. For instance, let’s say you want to sample 50% of a pool of 122 employees, or 61 employees total, spread over three samples in a year. In reality, 63 people will be tested that year. That’s because 50% of 122 is 61, divided by 3 is 20.33, and in order to meet minimum testing requirements, SYSTOC rounds up to the nearest whole number, or 21. So, 21 employees (not 20) will be tested each time. Because the test is run three times per year, and 21 times 3 is 63, then 63 employees, not 61, will be tested that year.
Alternate Rate
Alternates are those individuals who will be tested if any of the originally selected individuals are unavailable on the day of the drug or alcohol test. Like the sample rate, the alternates rate is expressed as a percentage of the overall pool size for the year. In other words, the number of alternates per year = Alternates Rate x Pool Size. To calculate the number of alternates per run, divide the number of alternates per year by samples per year.
You will want to ensure that you will always have enough employees to fulfill testing requirements. If the number of individuals in a pool is small, or the job is one where the employees are frequently unavailable, you may need to use a high alternates rate. For example, if you have a pool of 200 truck drivers to be sampled four times per year and a rate of 50%, each sample will contain 25 names. To guarantee that you will have 25 people to test, you may need to have a 50% alternates rate to yield an additional 25 names of potential testees.