Defense Intelligence Reference Document An Introduction To The Statistical Drake Equation

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ET _Distance between any two ncighbnring ET
Randnm variable Civilizati(]ns in Galaxy assuming they arc lJNirORMLY
di~tributed thrnughnut the wlmlc Galaxy vnlumc.
Prnhahilit,, distributinn Unnamed (Paul Davies Sil" rested ·'Maccune di.~trihutinn")
1:lnl fiRi,,.,.',\h,,, ,_, 1-,r
Prnhability density function '
I' ) 3 I --:>a-
. ET_Di,t.rn«:(r = - •--- ,,
' 5a
(Defining the positive numeric comtant C) C = v6 Rt"'"'' he"'"'' :::e 28845 light years
" o·
-
Mean value (Er _Di.~lanee) =Ce 3 e 18
'Variance a~T .2 - '/I 9 9, ,-[,' l
DLStana' -1 (T' a
-6/: r,, -4c ,, - 3c ,, + 12 c '
4a' " 2 (T-
K, - - -
Kurtosis --=c " + 2 C 3 +3c ' -6
(K,)'
Expression of JI in terms of the lower (11,) and upper _L' ( \_L' h,[ta(h;)-1]-a;[h,(a,)-1]
(b,) limits of the Drake uniform input random JI- Y,;-
1-l 1-l h; -a,
variables D,
Expression of a 2 in tcrms of the lowcr (a,J and upper ' ' a,h, [la (h, )- la (a, )]', L , CL'-(h,) limits of the Drake uniform input random a-= ar, (b, - a,)'
variables D,
,_, i-1
Table 3. Summary of the properties of the prohahility diqrihution that applies to the random variable ET _Distance
yielding the (average) distance between any two neighboring communicating civilizations in the Galaxy.
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