In order to understand carrier statistics in phosphorus-doped n-type diamond, electron statistics involving compensation and deep-dopant effect are theoretically analyzed. For n-diamond with a compensation ratio (c) larger than 1x10(4), the electron concentration (n) at room temperature (RT) is insensitive to the donor concentration (N-D) and reduced with increasing the c value. On the other hand, for diamond with a c value smaller than 1x10(4), the n value at RT increases with increasing the N-D value and is insensitive to the c value. Similarly, the length of Debye tailing (lambda(n)) at RT is reduced with increasing the c value for n-diamond with c > 1x10(-4) and is insensitive to the c value for n-diamond with c < 1x10(-4). However, it is found that an increase of temperature is effective to increase the n value and to reduce the X,, value. The n value as large as 10(15) cm(-3) and the lambda(n) value as small as 100 nm are expected to be achieved at an elevated temperature of 473 K.