The performance of the scintillation electron-detector is evaluated in terms of the output signal-to-noise ratio and detective quantum efficiency (DQE). An expression is presented which relates the statistical behaviour of each section of the detector in the STEM configuration to the DQE of the whole system and which also relates this DQE to the detector output signal. This expression is employed to correlate quantitatively the data measured using three types of scintillator under various operating conditions and also during scintillator deterioration caused by electron irradiation. It is shown that the influence of changes in design parameters on the DQE can then be predicted.