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What are the disadvantages of systematic sampling?
Disadvantages of systematic sampling: © The process of selection can interact with a hidden periodic trait within the population. If the sampling technique coincides with the periodicity of the trait, the sampling technique will no longer be random and representativeness of the sample is compromised.
To cut the maximum likely error in half the sample size should be?
... should be increased by a factor of 4. Note that this implies that the only errors are statistical (random) in nature; increasing the sample size won't improve systematic errors.
Is systematic sampling biased?
Often not, but it is important to check that there is no systematic pattern in the skip.To take an unlikely example, suppose you wanted to sample the values of 10% of houses on a street with 200 houses on it. A possible systematic sampling scheme would be to select a random house number to start with and then select every 20th house number (looping back when the number exceeds 200). If the first house number is odd then all houses in the sample are odd numbered and, therefore, on the same side of the street. If the street runs East-West, the sample could consist exclusively of South-facing gardens - attracting a price premium!
What is the definition of a systematic type of sampling in biology?
As the wikipedia article on this subject suggests, systematic sampling is most readily applied when potential sample elements are linearly ordered either in time or space. For example, one could choose to include every fifth customer arriving at a store in one's sample, which would be an instance where sample elements are ordered in time. The difficulty with many research situations in biology is obviously that sample elements are not linearly ordered. A herd of buffalo in a grassy field, for example, or a collection of microorganisms on a microscope slide. Remedies depend on circumstances. Suppose you want to apply systematic sampling in a small forest where you want to estimate the fraction of trees infested with a certain species of insect. You decide on, say, a one in five sample and that you will include 500 trees in your sampling frame in order to get a sample size of 100. To begin you walk enough parallel transects through the forest, marking sufficiently large trees as you go, to get your 500-tree sampling frame. Then you take a second trip through along transects to identify infested trees.
What is the difference between sample and sample size?
a sample is a sample sized piece given... a sample size is the amount given in one sample
