Compară metode

	Eșantionare Sistematică	Eșantionare sistematică proporțională
Domeniu	Metodologia anchetelor	Metodologia anchetelor
Familie	Process / pipeline	Process / pipeline
Anul apariției	Mid-20th century (Cochran 1953; Kish 1965)	Mid-20th century (formalized ~1950s–1970s)
Autorul original	William G. Cochran; formalized in survey sampling theory	Codified in classical survey sampling theory; see Cochran (1977)
Tip	Probability sampling design	Probability sampling design
Sursa seminală	Cochran, W. G. (1977). Sampling Techniques (3rd ed.). John Wiley & Sons. ISBN: 978-0471162407	Cochran, W. G. (1977). Sampling Techniques (3rd ed.). Wiley. ISBN: 978-0471162407
Denumiri alternative	interval sampling, systematic random sampling, equal-interval sampling, fixed-interval sampling	proportional 1-in-k sampling, equal-probability systematic sampling, proportionate systematic selection, PPS systematic sampling
Înrudite	5	6
Rezumat	Systematic sampling is a probability sampling technique in which every k-th element is selected from an ordered list of the population after a random starting point. With population size N and desired sample size n, the sampling interval k = N/n is computed and one unit is chosen at random from the first interval; all subsequent units are selected by adding k repeatedly. The method is operationally simple, yields a spread-out sample, and often achieves lower variance than simple random sampling when the list has no harmful periodicity.	Proportional systematic sampling combines systematic (every k-th element) selection with proportional allocation across subgroups, ensuring that each stratum contributes sample units in proportion to its share of the total population. The result is an equal-probability design that is administratively simple, spreads the sample evenly across an ordered frame, and eliminates the need for post-hoc weighting when strata are sampled at a uniform rate.