1. A computer implemented method of calculating a repeat sales home price index, the method comprising: calculating by a computer an X′X matrix of (T−1)×(T−1) dimension directly and calculating an X′Y matrix of (T−1)×1 dimension directly without constructing an X matrix; and determining by the computer a home price index using the formula {circumflex over (b)}=(X′X) −1 X′Y, wherein N is a number of sale pairs occurring within a duration of T time periods, the Y matrix is an N×1 matrix of the change in the log price of individual properties, the X matrix is an N×(T−1) matrix of 0, 1, or −1, and {circumflex over (b)} is a (T−1)×1 matrix of log price indices; outputting by the computer the determined home price index.