There are two thoughts about sample size How many respondents do I need for my online survey? that when a survey long a representative, a relatively small sample size is adequate.
The other point of view is that while maintaining a representative sample is essential, the more respondents you have, the better.
There is a big issue because it impacts all sorts of decisions, including the length of your survey, collection mechanism, and sampling rate.
The first steps in determining the sample size depend on the following factors:
How many people are in your population?
This is pretty simple. Your population is the total target audience or market whose views you’re interested in.
It could be anything from the total adult population to girls, men, or women between a certain age bracket as per the online survey, years old who hold graduate degrees to homeowners in the a given area.
How representative does your online survey results need to be?
This one is a bit trickier. The more straightforward way to look at it is, the closer your sample is concerning the total population, the more representative your results are likely to be.
If you surveyed every single homeowner in an area, you’d be pretty confident that your results represented the views of the whole home-owning population.
But since it’s almost impossible to survey 100% of any particular population, the next best thing is a well-designed survey where you have an acceptable level of tolerance for inaccuracy.
What margin of error should you use?
A margin of error is a percentage that tells you how much the results from your sample may deviate from the views of the overall population.
The smaller your margin of error, the closer your data reflects the population’s opinion at a given confidence level.
Generally speaking, the more people you gather data from, the smaller your margin of error. However, because it is rarely feasible to collect data from everyone in the population, some margin of error is necessary for most studies.
What is your online survey’s significance level?
The significance level is a percentage that tells you how confident you can be that the actual population value lies within your margin of error.
So, for example, if you are asking people whether they support a candidate for President, the significance level tells you how likely it is that the level of support for the candidate in the population falls within the margin of error found in your sample.
Expected significance levels in survey research are 90%, 95%, and 99%.
Once you know the values above, you can plug them into a sample size formula or, more conveniently, an estimator to determine your sample size.
How many people you should invite to survey
Sample size calculations tell you how many people you need to complete your survey. What they do not tell you, however, is how many people you need to invite to your survey.
To find that number, you need to consider the response rate.
For example, suppose you are conducting a study of customer satisfaction and know from previous experience that only about 30% of the people you contact will respond to your survey. In that case, you can determine how many people you should invite to the survey to determine your desired sample size.
