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 (ND) 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 ND value and is insensitive to the c value. Similarly, the length of Debye tailing (ln) 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 ln value. The n value as large as 1015 cm-3 and the ln value as small as 100 nm are expected to be achieved at an elevated temperature of 473 K.