StataCorp, 1995. Stata statistical software. Release 4.0. College Station, TX: Stata Corporation.
2.
Pickles A., Dunn, G., Vázquez-Barquero JL. Screening for stratification in two-phase ('two stage') epidemiological surveys. Statistical Methods in Medical Research1995; 4: 73-89.
3.
Lehtonen R., Pahkinen EJPractical methods for design and analysis of complex surveys. Chichester: John Wiley, 1995.
