is sample standard deviation unbiased
For example, we use the sample mean as an unbiased estimator for the population mean. (Mathematically, it can be shown that the expected value of the sample mean is equal to the population mean). In the case of estimating the population standard deviation, the sample standard deviation is an unbiased estimator too.
In statistical hypothesis testing, a test is said to be unbiased when the probability of committing a type I error (i.e. false positive) is equal to the significance level. Detection bias occurs when a phenomenon is more likely to be observed for a particular set of study subjects.