The Safety Monitor (in Dutch only) is a biennial national survey on crime victimisation. A sample of the Dutch population aged 15 and over are asked questions on such topics as the quality of their living environment, experienced nuisances in their neighbourhood, safety perceptions, crime victimisation, their level of satisfaction with the police and prevention.
The Safety Monitor is a sample survey. This means survey results have a reliability margin which, aside from the applicable confidence level and research design, mainly depends on the dispersion of answers and the number of persons questioned. The chosen confidence level is 95 percent. This implies that the actual values lie within the range between margins corresponding with the respective values found in 95 out of 100 samples.
Reliability margins in the Safety Monitor are small due to the large number of nationwide observations in the sample survey. In 2017, there were slightly under 150 thousand survey participants. Point estimates based on a sample survey of this scope have a margin of +/– 0.25 percentage point with an estimate of 50 percent. This means the probability is 95 percent that the actual value of this estimate lies between 49.75 percent and 50.25 percent. At lower regional level, these margins are wider, given the lower number of available observations for this purpose.
Differences in outcomes such as between regions and the nationwide average, or between various years, are statistically significant and therefore inherently meaningful, if such differences remain after the impact of discounting reliability margins corresponding with the outcomes.