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Also known as the Bradford-type law , distribution of first digits , distribution of most significant digits , first-digit problem , Law of anomalous numbers , log law of numbers , the probability mass function of the Benford distribution is given by
B
e
n
f
o
r
d
(
x
)
≡
Pr
(
X
=
x
)
=
log
(
1
x
+
1
)
log
(
10
)
{\displaystyle \mathrm {Benford} (x)\equiv \Pr(X=x)={\frac {\log \left({\frac {1}{x}}+1\right)}{\log(10)}}}
x
=
1
,
2
,
…
,
n
{\displaystyle x=1,2,\dots ,n}
Cumulative Distribution Function
F
X
(
x
)
=
log
(
x
+
1
)
log
(
10
)
{\displaystyle F_{X}(x)={\frac {\log(x+1)}{\log(10)}}}
Expected Value
E
(
X
)
=
10
−
log
(
3628800
)
log
(
10
)
=
3.44024
{\displaystyle \mathbb {E} (X)=10-{\frac {\log(3628800)}{\log(10)}}=3.44024}
Variance
Var
(
X
)
=
81
−
73
log
(
2
)
+
50
log
(
3
)
+
9
log
(
5
)
+
13
log
(
7
)
log
(
10
)
−
(
10
−
log
(
3628800
)
log
(
10
)
)
2
=
6.05651
{\displaystyle \operatorname {Var} (X)=81-{\frac {73\log(2)+50\log(3)+9\log(5)+13\log(7)}{\log(10)}}-\left(10-{\frac {\log(3628800)}{\log(10)}}\right)^{2}=6.05651}
Probability Generating Function
G
(
t
)
=
∑
x
=
1
9
t
x
log
(
1
+
1
x
)
log
(
10
)
{\displaystyle G(t)=\sum _{x=1}^{9}{\frac {t^{x}\log \left(1+{\frac {1}{x}}\right)}{\log(10)}}}
Interrelations [ edit ]
Symbol
Meaning
∼
{\displaystyle \sim }
X
∼
Y
{\displaystyle X\sim Y}
≡
{\displaystyle \equiv }
the distribution in the title is identical with this distribution
⇐
{\displaystyle \Leftarrow }
the distribution in title is a special case of this distribution
⇒
{\displaystyle \Rightarrow }
this distribution is a special case of the distribution in the title
←
{\displaystyle \leftarrow }
this distribution converges to the distribution in the title
→
{\displaystyle \rightarrow }
the distribution in the title converges to this distribution
Relationship
Distribution
When
⇐
{\displaystyle \Leftarrow }
Bradford
(
a
,
n
)
{\displaystyle \left(a,n\right)}
a
=
1
n
=
9
{\displaystyle a=1\quad n=9}
←
{\displaystyle \leftarrow }
Adhikari-Sarkar (type 1)
(
n
)
{\displaystyle \left(n\right)}
n
→
∞
{\displaystyle n\rightarrow \infty }
←
{\displaystyle \leftarrow }
Adhikari-Sarkar (type 2)
(
n
)
{\displaystyle \left(n\right)}
n
→
0
{\displaystyle n\rightarrow 0}
←
{\displaystyle \leftarrow }
Furlan's spectrum of power numbers
(
k
,
r
,
R
,
w
)
{\displaystyle \left(k,r,R,w\right)}
k
=
9
R
=
1
w
=
0
r
→
∞
{\displaystyle k=9\qquad R=1\qquad w=0\qquad r\rightarrow \infty }
←
{\displaystyle \leftarrow }
Uppuluri-Patil (type 1)
(
j
,
m
,
n
)
{\displaystyle \left(j,m,n\right)}
j
=
1
n
=
1
m
→
∞
{\displaystyle j=1\qquad n=1\qquad m\rightarrow \infty }
←
{\displaystyle \leftarrow }
Uppuluri-Patil (type 2)
(
j
,
m
,
n
)
{\displaystyle \left(j,m,n\right)}
j
=
1
n
=
1
m
→
∞
{\displaystyle j=1\qquad n=1\qquad m\rightarrow \infty }
←
{\displaystyle \leftarrow }
Uppuluri-Patil (type 3)
(
j
,
m
)
{\displaystyle \left(j,m\right)}
j
=
1
m
→
0
{\displaystyle j=1\qquad m\rightarrow 0}
References [ edit ] 
