15.3.2 The two-Poisson model

• 2 $B$D$N(B poisson distribution $B$NAH$_9g$o$;(B
• 2$B$D$N(B document class
  • non-privileged class $\rightarrow$ w_i $B$,=P8=$7$K$/$$(B document $B=89g(B
  • privileged class $\rightarrow$ w_i$B$,=P8=$7$d$9$$(B document $B=89g(B
  
  
  $$\begin{eqnarray*}tp(k;\pi;\lambda_1,\lambda_2) = \pi e^{-\lambda_1} \frac{\lambda_1^k}{k!} + (1-\pi )e^{-\lambda_2} \frac{\lambda_2^k}{k!} \end{eqnarray*}$$
  
  $\pi$ $\rightarrow$ privileged class $B$KB0$9$k3NN((B
  
  ($BNc(B)
  privillaged class $B$N(B document $B=89g$r(B w_i $B$,(B m $B2s0J>e=P8=$9$k(B document $B=89g$H$9$k(B, $\pi,\lambda_1,\lambda_2$ $B$,7h$^$k(B
• non-privileged class $B$G$O(B w_i $B$N=P8=$O6vA3(B, non-content word
• privileged class $B$G$O(B, w_i $B$N=P8=$OI,A3(B, content word
• $B$"$k$G$O(B $B3NN($,6K>.$K$J$kIQEY$O(B 2$B$@$HJ,$+$C$?(B,
  $B$7$+$70lHL$K3NN($OC1D48:>/(B $\rightarrow$ negative binominal $B$J$I$rAH$_9g$o$;$F?dDj(B