In Germany, no directory is generally available that contains the addresses of all private households or individuals, which could be used by market research agencies as a sampling frame. The data collected by the local authorities are only available for surveys considered to be of “public interest”.
The “Arbeitsgemeinschaft ADM-Stichproben Face-to-Face” (a group of agencies that is responsible for the sampling system) closes this gap by providing a sampling frame to member agencies. This frame allows representative face-to-face samples to be drawn for all households in Germany and for all people living in those households. In addition, the main statistical data are provided on a detailed level for this population.
The ADM-Sampling-System (F2F) is designed as an area sample covering all populated areas of Germany. It is based on Germany’s topology, organized by states, counties and communities, the statistical areas within communities described by public data, and the geographical data created for traffic navigation systems. Combining these data, the area sample is made up of about 53000 areas, each containing at least 350 but on average about 700 private households.
Prior to sampling, the areas are first regionally stratified according to counties and so-called BIK types1) resulting in some 1500 strata. Based on this stratification, 128 “nets” are extracted containing 210 areas in former West Germany and 48 in former East Germany. These 258 sampling points (= areas) are drawn proportionally to the distribution of private households. For optimal utilization of the stratified sampling frame, sampling is done using the method for random allocation developed by L. H. Cox.2) The key advantage of this method is that it leads to stratified samples without any accumulation of rounding effects. As one area is drawn for one net only and rounding effects are minimized by the Cox allocation, any selected net may be combined with any other selected net, without issues such as differing selection probabilities or too high rounding differences arising. The ADM-Sampling-System (F2F) provides member agencies with as many nets as they need to carry out their surveys.
In the second step, and where necessary in the third step too, the private households (2nd step) and within them the individuals (3rd step) to be polled, are selected randomly using systematic selection methods with a random start. Such methods are known as “random walk”, “address listing with random selection”, “Kish tableau”, “next/last birthday” and others. (These two steps are performed by the agencies themselves)
Since the sampling is done randomly in all three steps (area sampling, household selection, selection of target persons), this method for face-to-face surveys is based entirely on random
sampling. Therefore surveys based on this ADM-Sampling-System (F2F) fully meet the scientific requirements regarding randomization based on statistical theory.
Spokesperson of ADM Sampling Systems, July 2009
1) Types of communities differentiated according to the number of inhabitants and the proximity to the nearest conurbation 2) cf. L. H. Cox; A constructive procedure for unbiased controlled rounding; in: Journal of the American Statistical Association 82, S.520 – 524, 1987