A quota sample is one in which respondents are selected according to predetermined characteristics that reflect the population as a whole. In a judgment sample , members of the population are selected on the basis of what the researcher believes will be a good sample. With nonprobability samples, you can't measure how the results differ from the entire population. Observation is watching and recording the actions of the people, objects, or events being studied. Nearly all marketers use informal observation to get clues to customer buying behavior and competitive actions.
Informal observation can help in narrowing a marketing problem.
However, it can lead to sampling errors. You can use a survey to collect data by asking the target population a series of questions. To question the sample respondents over time, marketers use a panel , a group of people who participate in a series of surveys. This also allows marketers to establish a dialogue with respondents. Limited contact reduces the possibility of bias.