The short-time unbiased spectrum estimation (STUSE) algorithm is analyzed and expressions for the mean and variance of the spectrum estimates are derived. The STUSE algorithm deliberately adds biased spectrum estimates in order to yield unbiased estimates and at the same time have excellent spectral leakage suppression capabilities. Computer simulations are presented, verifying the theoretical results and also comparing the STUSE algorithm with the conventional weighted, overlapped, segment averaging (WOSA) method.