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Sample Sizes In Qualitative And Quantitative Research

Article Summary: In quantitative research, sample sizes are much higher than in qualitative studies, where researchers are not relying on statistics. Sample sizes in qualitative research can be considerably lower, even as low as 8-15 participants per segment. In quantitative research, sample sizes typically start at 200 for a safe confidence interval.

When conducting a qualitative or quantitative market research study, one of the first considerations for the researcher is the sample size of the target population to recruit. Recruiting too few or too many participants for any study will yield results that are skewed and meaningless. Market research is an investment that when done properly can provide deeper insights into market trends, customer values and motivations, and how a product or service is perceived. 

What’s the difference again between Qualitative and Quantitative Market Research?

Before we delve into sample sizes between quantitative and qualitative studies, it’s good to give a refresher on what the difference between these two study types are. 

Qualitative research seeks to understand – through focus groups, in-depth interviews, or mobile ethnographies – why and how consumers behave and think the way that they do, especially as it relates to a product, brand, or service. Qualitative research is less definable than quantitative research, but that doesn’t mean it is less important. Qualitative market studies explore the what, why, and how rather than how many, which is what quantitative research answers. The insights gained from qualitative methods can and do transform how a business operates. Everything from branding and messaging, to product development, positioning, pricing, and customer service are well served with qualitative research.

Quantitative research seeks to measure the proportion of a population within a market segment that thinks or behaves the way that they do. The core of quantitative research is counting – how many people buy from a specific brand, or how many agree with a statement? Quantitative research yields copious amounts of data that we make sense of by using statistics to draw conclusions. From there we’re able to segregate and aggregate the data into categories and types. Quantitative research is very useful, particularly when clients want to understand larger patterns. Quantitative results aren’t the end point though, and should be combined with qualitative market research to better understand opinions, as well as the why’s, what’s, and how’s.

What’s the sample size for qualitative studies?

In the earliest stages of designing a qualitative or quantitative study, the market researcher is thinking about sample sizes and recruiting. A qualitative study is hard to conduct with too many participants, especially if focus groups are used, and quantitative studies are worthless if too few participants are involved. There is no hard-and-fast rule that says that every qualitative or quantitative study should have X amount of participants, but there are definitely ranges that have been proven out over time.

Since fewer participants are required for qualitative market research studies, what matters more is quality, not quantity. Before we determine an ideal sample size for qualitative studies, we define four values that guide us to the ideal number of participants to recruit. If math and numbers are your thing, you can read more about these four values in this past blog post on sampling in market research

Each qualitative study will have slightly different sampling targets, but typically they fall between 8-15 participants (per segment/persona), assuming you are targeting similar segments within a population. With a smaller sample size for qualitative research, we can’t emphasize enough how important the quality of the recruited participants is! 

What’s the minimum sample size for a quantitative study?

The minimum sample size for a quantitative survey depends on several factors, including the population size, desired level of confidence interval, margin of error, and the variability within the population. To determine the minimum sample size, you can use statistical formulas, with the most common one being the formula for calculating the sample size for estimating a population proportion (p) with a specified level of confidence and margin of error. 

Keep in mind that this formula assumes a simple random sample and certain assumptions about the population distribution. If your survey has a complex sampling design or you’re dealing with a finite population (rather than an infinite one), you may need to use different formulas or adjustments.

In practice, it’s often advisable to consult with a statistician or use statistical software/tools to calculate the appropriate sample size for your specific survey, taking into account the relevant parameters and any potential complexities. Additionally, a larger sample size generally leads to more accurate estimates but also requires more resources, so it’s important to strike a balance between precision and cost when determining your sample size. 

At InterQ, our standard survey size starts at 200, but this depends on many variables, including the variance in the population being studied. If your study covers a large geographic area, or includes multiple customer segmentations, then you’ll need a much larger sample size. For very homogeneous samples, you can go as low as a sample size of 40.

InterQ is fortunate to have a team member, whose sole job is managing our quantitative studies. Her expertise in quantitative data analysis and study design is unparalleled. 

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Author Bio: Joanna Jones is the founder and CEO of InterQ Research. At InterQ, she oversees study design, manages clients, and moderators studies.