Methods and apparatuses are provided that may be implemented in various electronic devices to possibly reduce a first-time-to-fix and/or otherwise increase the performance or efficiency of a device in determining its current estimated position. In some embodiments, it may be determined whether current estimated position is valid based, at least in part, on pseudorange measurement information and pseudorange predicted information, and such determining may include obtaining a sum-of-squares of an a-posteriori measurement residual associated with the pseudorange measurement information and the pseudorange predicted information.