Smart Sampling: Use an appropriate sample frame to achieve useful results

Sampling is a fundamental component of market research; it is the principle that a part of a population—a sample—can be used to make conclusions about a complete group. By relying on a subset of the population to represent the opinion of all, researchers can gather vital information from key market segments more efficiently.

Yet useful research results depend on an appropriate and high-quality sample. So, before making any decisions about who, when, where or how to sample, be clear about why you’re conducting research and what you need to know. Identify how you will use the results of your research project.

For instance, do you plan to define market segments based on the research results, or do you need results to be presented in context of known variables or segments? Your answers to questions like this can help you streamline your project by making sound decisions about sampling, including who to include and how to reach them.

Based on your set of finely tuned objectives, identify the population your study will target. Be sure to define this population with tangible characteristics (e.g., oncologists practicing in the United States who are either non-users of your brand or categorized in deciles six through ten based on their prescribing behavior). This will keep your study focused and your budget on track.

The list of all potential respondents for your study, representing a functional census of your target population, is known as your sampling frame; it is the population from which your sample is drawn. The term functional is used as a condition, since it is nearly impossible to achieve a perfect listing of any population. Examples of sampling frames include sales rep call lists, patients diagnosed with a certain disease, people in selected zip codes, etc. People not in the frame have no prospect of being sampled.

Bio-pharmaceutical market research studies typically use either a client-supplied list or purchased list as the sampling frame. Each type of list has advantages and disadvantages. To determine which is the best for your study, consider and weigh the following issues:

Practical

First and foremost, make sure your sampling frame is appropriate for the population you want to study. Before committing to a specific list, ask the following questions:

• How old is the list?
• How was it developed?
• Does it reflect the target population for this study?
• How does the list compare to alternative sample frames?

As mentioned above, m ost sampling frames are functional representations of a target population; they rarely portray the actual population. They exclude some members of the population and incorrectly include some who do not belong.

For example, a pharmaceutical company’s list of specialty doctors who meet with its reps may exclude physicians who are new to a practice. Conversely, it may include retired physicians and those who’ve been removed from the medical board. Identifying a sampling frame that truly represents your target population requires the expert judgment of people who understand your business issues and marketplace.

Economical

While less expensive up front, client-supplied lists can often cost much more in the long run. They are typically not as complete or up-to-date as purchased lists. For example, if your sales force physician call list does not include accurate and complete information for each physician on the list, you will end up paying your research provider to gather or update this information.

In another case, if you have a specialty brand that targets a vari