Listening to Your Customers: Selection Customers to Participate in Interviews, Focus Groups and Surveys
Generally, random samples are the best way to ensure that the sample represents all your customers. This means that you can safely assume that the patterns you see in your fi ndings are the same as the patterns you would have seen had you contacted all your customers. Random sampling means that each customer has an equal probability of being selected into the sample. This works best if you have a complete list of your customers.
To create a random sample, you need to:
- Find or create a list of all your customers.
- Determine how many customers you have and how many you need to contact. For example, you have 500 customers, and you want to contact 100 of them. You need to randomly select 100/500 or 1 in 5.
- Randomly select the members of your sample. To do this, you will need a random number table or a computer program that generates random numbers. (One online program is: http:// www.randomizer.org.) First, number your customers. From the random number table, or using the computer program, select one set of 100 random numbers, ranging from 1 to 500. Those customers whose numbers match the random numbers are selected for the sample.
A ‘shortcut’ is called systematic sampling:
- Create a list of all your customers. Make sure the list isn’t in a particular order (for example, by alphabet, by zip code, by number of years as a customer). Number each customer on the list.
- Calculate the sampling interval, by dividing the total number of customers in your list by the number of customers you plan to sample. Using the same example as above, the sampling interval would be 500/100, or 5.
- Select a random number (from a random number table or from a computer program). This number gives you the starting place on your list. For example, a random number table gave the number 22. Find the 22nd name on the list. This is the first name for your sample.
- From this starting point, count the number of customers that match your sampling interval. That next customer name becomes part of your sample. To continue the example, starting at the 22nd name, select every 5th (sampling interval) name for your sample. The first name in your sample would be number 22, the next would be 22 + 5 = 27, the third would be 27 + 5 = 32, and so on.
- If you come to the end of your list but haven’t selected your entire sample, start over, continuing with the sample sampling interval until you have the total number you need.
Approaches not based on random sampling techniques may also be used. These are appropriate when you don’t have contact information for your customers, or when you’re interested in information from a specific set of customers.
- Convenience samples are those where individuals are selected because they are accessible. This would include visitors to your booth at the farmers’ market, or individuals who attend a local foods fair.
- Snowball samples are based on referrals. For example, you might want to assess interest in a local foods network. You would interview a small number of people who run farm businesses or retail/ wholesale outlets in the area, then ask them for additional names of people who might be interested. Keep interviewing until you start hearing the same names over and over.
- Purposive samples are drawn by identifying people who meet specific characteristics. For example, you are interested in knowing if your customers who buy tomatoes would be interested in processed tomato products (salsa, tomato sauce, etc.). You would contact these customers and conduct a short telephone interview to assess their interest in the processed products.
The limitation of these non-probabilistic approaches is the potential for bias in the results because not every individual has an equal chance to be chosen. For example, you might give a survey to people who purchase products during one day at the farmers’ market. However, this approach excludes all those who did not attend the farmers market that day and all those who did not buy products. The survey results would only represent the small subset of people who purchased products that particular day, and not all customers of your booth.
You should decide if obtaining a random sample is important or not. This decision can be based on your reason for gathering feedback as well as the practical costs of doing so. Regardless of your ultimate choice. Some thought should be given to the appropriate sample size and how you will obtain your sample.
TitleListening to Your Customers: Selection Customers to Participate in Interviews, Focus Groups and Surveys
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