Q: Is there any bias in the sampling for my study?
My required sample is only 524 out of 1200. A sampling interval of two was used as the constant difference between subjects. The first starting number of two was picked randomly using the lottery method from the registration. Is there any bias in my sampling?
Please note that we have made some edits to your question as the last part seemed incomplete and also for enhanced clarity. Due to this, we have responded to the best of our understanding.
It appears that you are following systematic sampling, given the population size (1,200), sample size (524), and interval size (2), with the first sample (#2) being chosen at random. So, is it possible to check if the list of subjects from which you are to pick samples is random?
When using systematic sampling (which involves selecting members of the population at a predetermined regular interval), if the population order is random or random-like (e.g., alphabetical), this method will give you a representative sample. If, however, the list follows a pattern or is in some sort of periodic or cyclic order (say, with male and female subjects being listed alternately), this sampling could lead to a bias (such as through the selection of only one sex, owing to the interval of 2). So, if you are sure that the subject list is random, especially without alternating the pattern (considering that your interval is 2), the sampling should be truly representative, with a very low chance of bias.
For more insights on sampling and biases, you may also find the following resources helpful:
- What would be the right sampling technique for a research involving multiple case studies?
- If we use a convenience sample, how should we mention the sample size calculation in the Methods section?
- How should I respond to a reviewer's comment regarding selection bias?
- 7 Biases to avoid in qualitative research
And for further help with experimental design and statistics, you may learn more about our relevant services here:
Hope that helps. All the best for your study!