Metodo di campionamento sistematico

Appropriate sampling methods ensure that samples are drawn without bias and truly represent the population. 

Systematic sampling is one of the simplest methods of sample collection. In systematic sampling, sample selection is purely based on the position and not on sample characteristics such as color, gender, or physical appearance. 

Suppose, from a class roster of twenty students, four of them need to be randomly selected to calculate the average height of students in the class. 

Simply divide the population size, twenty, by the desired size of the sample, four, to obtain a systematic interval—a fixed periodic interval for drawing samples. 

Now, select every 5th person from the list to get the systematic sample of students and calculate the average height. 

Systematic sampling can only be used when researchers know the exact number of individuals in a population. Also, the population must be randomly distributed to avoid bias.

For instance, if all tall students in the class are standing together, the systematic sampling would draw a biased sample, reducing the average height of the class.