How To Decide The Sample Size For An Online Survey?

How To Decide The Sample Size For An Online Survey

The sample size for a research study needs to be determined when the research study is proposed. If your sample size is too small, it may result in a disproportionate number of individuals that don’t provide a clear and accurate picture of the whole population. Also, if your sample size is too large, the whole research study becomes time-consuming and even expensive. So, how to determine an effective sample size? How to consider the right respondents for your research survey? In this blog, we’ll help you determine the effective sample size for an online survey.


What is Sample Size?


Sample size is determined as the number of individuals included in a research study that represents the whole target population. The sample size refers to the total number of respondents included in the research study, and these respondents are often divided into subgroups based on demographics, such as age, gender, geolocation.


Why is it important to determine effective sample size?


Let’s consider, you want to launch a new Bluetooth earphone in India and for this you want to conduct a survey to understand your customers preferences towards Bluetooth earphones. It’s impossible to send and ask 1.39 billion people. Also, it could be a waste of resources, time, and money and the result will not be conclusive since it includes all age groups that may or may not be using the Bluetooth earphones. For this, you need to use a sample size determination formula to select an effective sample size that fits into the consumer panel requirement. You can use their responses to help determine the review of your product in the market.


How to determine effective sample size for an online survey?


Before we start determining the sample size, here are some basic factors that you need to understand that plays an important role in your survey research:


Population Size:


Population size is basically the people that fit your demographics. For example, as we discussed earlier, a survey that you want to conduct before launching your Bluetooth earphone should include only those people that use earphones or want to buy new earphones. Calculating the exact number of people shouldn’t be a criteria. It’s common to choose an estimated range of people.


Confidence Level:


Confidence level deals with how confident you can be that your data is exact and correct. It is expressed in a percentage term and the most commonly used confidence levels are 90%, 95%, and 99% confident.


Margin Of Error


No research survey can be 100% accurate. Margin of error is basically expressed in terms of the mean number that tells you the difference between the mean number of your sample and the mean of your population.


Standard deviation


Standard deviation determines how much the responses that you receive will differ from each other and from the mean number. A high standard deviation means that all the values are spread over a wide range with small and large outlying figures whereas low standard deviation states that all the values are close together around the mean number. 

Sample Size For An Online Survey

Now, let’s determine the sample size for your research survey

Search your Z-score

To find the sample size, you need to first turn your confidence level into a Z-score. Generally, for the most confidence level, the Z-score is:

For 90%, Z Score = 1.645

For 95%, Z Score = 1.96

For 99%, Z Score = 2.576

For different confidence levels, various online tools can be used to find the Z-score.

Now, when you got the Z-score, standard of deviation, and confidence interval, use the sample size formula:

Necessary Sample Size = (Z-score)2 x Standard Deviation(1-Standard Deviation) / (margin of error)2

This equation should be used when the size of the population is very large. If the population size is smaller, use the sample size calculator. 

Let’s suppose you chose a 99% confidence level, .6 standard deviation and margin of error is +/-6%

Then, Necessary Sample Size = (2.576)2 x .6(.4)/(.04)2 = (6.635776 x .24)/0.0016 = 995.37.


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