ICCS 2009 Technical Report - IEA

In a small number of countries, the selected school sample contained some schools where morethan one classroom was selected. For these schools, the participation requirement was modifiedas follows:• A sampled class was regarded as a “participating class” if at least 50 percent of its studentsparticipated.• A sampled school was regarded as a “participating school” if all sampled classesparticipated.In four ICCS countries (Cyprus, Liechtenstein, Luxembourg, and Malta), all of the schools inthe population were selected for the study. Usually, more than one class per school was selectedin these countries, and the primary sampling units were classes, rather than schools. The classparticipation requirement applied in these countries, too; however, if one or more classesdid not participate in a school from one of these countries, the school was not automaticallyregarded as a non-participant.Whenever there was an indication that the survey operation procedures in a school were notproperly followed, the school was regarded as non-participant. For example, if a school had notlisted all their eligible classes for class sample selection, the corresponding student data fromthat school were not included in the ICCS database.Teacher survey participation requirementsSimilar to the process used for the student survey, each school had to meet a minimum teacherparticipation requirement to be counted as participating.• A school was regarded as a “participating school” in the teacher survey if at least 50percent of its sampled teachers had participated.• If a school did not meet this requirement, it was regarded as a non-participant with respectto the teacher survey.If the survey operation procedures in a school were not followed properly, the school wasregarded as non-participating. For example, if a school had not listed all of their eligibleteachers for teacher sample selection, or if the teacher selection procedures had not beenfollowed, that school’s respective teacher data were not included in the ICCS database.Calculating student weightsThe ICCS student weight is a product of several weight components. Generally, it is possible todiscriminate between two different types of weight components:• Base weights reflect the selection probabilities of sampled units. At each level of sampleselection, the base weight is the inverse of the selection probability of a sampled unit.• Non-response adjustments aim to compensate the potential for bias due to non-participationof sampled units.School base weight (WGTFAC1)The first stage of sampling for ICCS involved selecting the schools in each country. The schoolbase weight reflects the selection probabilities of this sampling step. When explicit stratificationwas used, the school samples were selected independently in each explicit stratum h, withh =1,…, H. If no explicit strata were formed, the entire country was regarded as being oneexplicit stratum.In most countries, ICCS drew a systematic sample of schools, with the selection probabilityof school i being proportional to its school size. Usually, the measure of school size M hiwasdefined by the number of students in the ICCS target grade. If schools were small (smaller than70ICCS 2009 technical report