ICCS 2009 Technical Report - IEA

the average class size in the explicit stratum), the measure of size M hiwas defined as the averagesize of all small schools in that stratum.The school base weight was defined as the inverse of the school’s selection probability. Forschool i in stratum h, the school base weight was given by:M hWGTFAC1 hi= sn hx M hiswhere n his the number of sampled schools in stratum h, M his the total number of studentsenrolled in the schools of explicit stratum h, and M hiis the measure of size of the selectedschool i.In the Russian Federation, the first sampling stage involved selection of regions. Therefore, eachschool weight was multiplied by a region weight component that reflected the probability ofselecting that region.School non-response adjustment (WGTADJ1S)Given the fact that some schools refused to participate in ICCS or had to be removed fromthe international dataset, the school base weights had to be adjusted to account for the samplesize loss. Adjustments were calculated within non-response groups defined by the explicitstrata. Within each explicit stratum, a school non-response adjustment was calculated for eachparticipating school i in stratum h as:s,enWGTADJ1S hi=hp-std nhs,e p-stdwhere n his the number of sampled eligible schools and n his the number of participatingschools in the student survey in explicit stratum h.s,e s s,eThe number n hin this section is not necessarily equal to n hin the preceding section, as n hwasrestricted to schools deemed eligible in ICCS. Because there was a lapse of one or two yearsbetween the school sampling and the actual ICCS test, some selected schools were no longereligible for participation in ICCS. This happened if a school had recently closed, did not havetarget grade students, or had enrolled only excluded students. In these cases, the ineligibleschool was not taken into account when calculating the non-response adjustment.Class base weight (WGTFAC2S)In each participating school, Windows ® Within-School Sampling Software (WinW3S, IEA DPC,2008) was used to randomly select one or more classes. More specifically, this process involveda systematic random method with equal selection probabilities for each class. In this samplingstep, the class base weight is the inverse of the selection probability.For each sampled class j, the class base weight was given by:CWGTFAC2S hij=his chiwhere C hiis the total number of classes with eligible students enrolled in the target grade and c hisis the number of sampled classes in school i in stratum h.SAMPLING WEIGHTS AND PARTICIPATION RATES71