Definitional elimination:
The significance level is a threshold used in hypothesis testing to decide when to reject a null hypothesis, it is not a direct measurement of sampling error. The confidence level expresses how often a confidence interval would contain the true parameter across repeated sampling, it describes reliability of the interval, not the size of the error itself. Validation of data concerns checking whether recorded data is accurate and consistent, unrelated to sampling error.
By contrast, the precision of a sampling plan is directly tied to the standard error of the estimate, roughly \( \text{Precision} \propto \frac{1}{\sqrt{n}} \), a smaller standard error means higher precision and a smaller sampling error. This is the only option that measures the error itself rather than a related but distinct statistical concept.
Hence, option (3) is correct.