It is not always necessary to speak to everyone to get a representative picture. Especially with large numbers, such as the voting behavior of all Dutch citizens, a representative sample is drawn. A representative sample contains a sufficient number of respondents. Be aware of drop-outs; not everyone in the selection will cooperate with your survey, and all subgroups should be represented, men-women, young-old, ...
You can draw your sample from a database of addresses (and background characteristics), such as ticket ordering service (theater) or a purchased address file. You can also ask people directly for your visit, for instance, at the entrance/exit of a museum/theatre. In this case, you determine in an objective way who is asked, for example, by asking every 5th person.
- To ensure that your sample is large enough, you first need to know the minimum number of people who should participate in your study. This depends on the size of your research population, the reliability you are aiming for, and the margin of error you are willing to accept. Calculating your required sample size is done with a sample calculator.
- Next, you need to assess the likelihood of people cooperating with your research. People on the street are less likely to cooperate with your research than if they have an affinity with the subject (e.g., the theater they frequent) or if the questionnaire is done in a classroom setting. Based on this, you will determine how many people you should ask.
- Then you're going to see if you have any subgroups in your research population. You can take this into account when drawing the sample or check and correct it afterward. If you take this into account beforehand, you will draw a selective sample. Consider which subgroups you want to take into account and how large these groups are. This is especially easy if you have a database with addresses and characteristics. But also, if you approach respondents directly (e.g., at the entrance of the museum), you can take this into account (only ask men or mjk holders).
Afterward, when you check for proper representation of the subgroups, you draw an a-selective sample. With the completed questionnaires, you're going to check that all subgroups are equally represented.