Definition
A probability sampling technique in which the sample is chosen by selecting a random starting point and then picking every ith element in succession from the sampling frame.
Explanation
In systematic sampling, the sample is chosen by selecting a random starting point and then picking every ith element in succession from the sampling frame. The sampling interval, i, is determined by dividing the population size N by the sample size n and rounding to the nearest integer.
Example
Suppose there are 100,000 elements in the population and a sample of 1000 desired. In this case the sampling interval, i, is 100. A random number between 1 to 100 is selected. If say number 23 is selected, the sample will then consists of elements 23, 123, 223, 323, 423, 523, and so on.
Systematic sampling is similar to SRS in that each population element has a known and equal probability of selection. However, it is different from SRS in that only the permissible samples of size n that can be drawn have a known and equal probability of selection. The remaining samples of size n have a zero probability of being selected.
For systematic sampling, the researcher assumes that the population elements are ordered in some respect. In some cases the ordering (alphabetic listing in a telephone book) is unrelated to the characteristic of interest. In other instances, the ordering is directly related to the characteristic under investigation. (Credit card customers may be listed in order of outstanding balances. If the population elements are arranged in a manner unrelated to the characteristic of interest, systematic sampling will yield result quite similar to SRS.
On the other hand, when the ordering of the element is related to the characteristic of interest, systematic sampling increases the representatives of the sample.
Advantages
• Systematic sampling is less costly and easier that SRS, because random selection is done only once.
• The random numbers do not have to be matched with individual element as in SRS. Since some lists contains millions of elements, considerable time can be saved. This in turn again reduces the cost.
• If the information related to the characteristic of interest is available for the population, systematic sampling can be used to obtain a more representative and reliable sample than SRS.
• Systematic sampling can even be used without knowledge of the composition (elements) of the sampling frame.
A probability sampling technique in which the sample is chosen by selecting a random starting point and then picking every ith element in succession from the sampling frame.
Explanation
In systematic sampling, the sample is chosen by selecting a random starting point and then picking every ith element in succession from the sampling frame. The sampling interval, i, is determined by dividing the population size N by the sample size n and rounding to the nearest integer.
Example
Suppose there are 100,000 elements in the population and a sample of 1000 desired. In this case the sampling interval, i, is 100. A random number between 1 to 100 is selected. If say number 23 is selected, the sample will then consists of elements 23, 123, 223, 323, 423, 523, and so on.
Systematic sampling is similar to SRS in that each population element has a known and equal probability of selection. However, it is different from SRS in that only the permissible samples of size n that can be drawn have a known and equal probability of selection. The remaining samples of size n have a zero probability of being selected.
For systematic sampling, the researcher assumes that the population elements are ordered in some respect. In some cases the ordering (alphabetic listing in a telephone book) is unrelated to the characteristic of interest. In other instances, the ordering is directly related to the characteristic under investigation. (Credit card customers may be listed in order of outstanding balances. If the population elements are arranged in a manner unrelated to the characteristic of interest, systematic sampling will yield result quite similar to SRS.
On the other hand, when the ordering of the element is related to the characteristic of interest, systematic sampling increases the representatives of the sample.
Advantages
• Systematic sampling is less costly and easier that SRS, because random selection is done only once.
• The random numbers do not have to be matched with individual element as in SRS. Since some lists contains millions of elements, considerable time can be saved. This in turn again reduces the cost.
• If the information related to the characteristic of interest is available for the population, systematic sampling can be used to obtain a more representative and reliable sample than SRS.
• Systematic sampling can even be used without knowledge of the composition (elements) of the sampling frame.