what does stratified sample mean in maths
'Strata' means 'layer'. A stratified sample is made up of different 'layers' of the population, for example, selecting samples from different age groups. The sample size for each layer is proportional to the size of the 'layer'.This is shown in the following equation:o work out the sample size for year 7: 1  There are 180 students in year 7 - this is the size of the layer. 2  There are 1000 pupils in the school-this the size of the whole population.