When you conduct interviews, you can find out a lot. You collect primarily qualitative data. (There are some tricks to collect quantitative data as well.) Before you start an interview, it is crucial that you have well-defined interview questions. Because you don't ask questions just for fun: respondents have to answer the central question of your research. That is why I am giving you tips on how to design your interview questions as well as possible:
Finally, I would like to inform you that remaining objective during the interview is essential. Your own opinion plays no role in this; make sure the interviewee can tell their own story.
More tips to prepare for your interview? Then please read my blog '15 tips for a good interview'.
Suppose you want to research a target group of as many as 10,000 people. Do you have to interview all 10,000 people to get the right results? Certainly not; only a part of the research population needs to participate in your research to get representative results. Let me explain what representativeness means and when the results are deemed characteristic.
Representativeness means the degree to which the respondents in a sample group are a good reflection of the target group of your research. Therefore, your research is representative, which means that the conclusion of your research is true for 'everyone' in your research population.
If you have a research population of 10,000 people, you will ultimately need to interview 400 people to arrive at the opinion of the larger group. This does not mean that you only need to approach 400 people. You have to deal with a response rate. This is the percentage of people who participate in your survey. Your response rate depends on the subject you are researching, how easy and fun it is to participate in your research, and what people get in return. I often use a response rate of 30% because I usually research fun subjects, and I am experienced in making it easy to participate in a survey. I also ask the client for a nice gift for the people who participate in the survey. Tips to increase your response rate
Because not everyone will participate in your survey, you will need to have a larger sample group. If you need 400 respondents and assume a response rate of 30%, you will need to interview a sample group of 400/30%=1,333.
When you conduct a survey, you must keep in mind that the smaller the research population is, the larger the number of respondents will be to arrive at the desired representative results. Sometimes, however, respondents' input is more valuable than the number of participants. In this case, you're referring to qualitative research, and it can be more important to focus on the research results than the representativeness in some cases.
If you want to know how many respondents you need for your research population: go to a sample calculator. These will often immediately tell you how many people you need to approach in your sample.