NAG Library Manual, Mark 28.5
```    Program g07abfe

!     G07ABF Example Program Text

!     Mark 28.5 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: g07abf, nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: clevel, sum_nag, tl, tu, xmean
Integer                          :: ifail, ifreq, n, num
!     .. Intrinsic Procedures ..
Intrinsic                        :: real
!     .. Executable Statements ..
Write (nout,*) 'G07ABF Example Program Results'
Write (nout,*)

!     Skip heading in data file

!     Read in counts and frequencies
sum_nag = 0.0E0_nag_wp
n = 0
d_lp: Do
If (ifail/=0) Then
Exit d_lp
End If

!       Calculate sum
sum_nag = sum_nag + real(num,kind=nag_wp)*real(ifreq,kind=nag_wp)
n = n + ifreq
End Do d_lp

!     Estimate Poisson parameter
xmean = sum_nag/real(n,kind=nag_wp)
Write (nout,99999) 'The point estimate of the Poisson parameter =',      &
xmean
Write (nout,*)

!     Calculate 95% confidence interval
clevel = 0.95E0_nag_wp
ifail = 0
Call g07abf(n,xmean,clevel,tl,tu,ifail)

!     Display CI
Write (nout,*) '95 percent Confidence Interval for the estimate'
Write (nout,99998) '(', tl, ' ,', tu, ' )'
Write (nout,*)

!     Calculate 99% confidence interval
clevel = 0.99E0_nag_wp
ifail = 0
Call g07abf(n,xmean,clevel,tl,tu,ifail)

!     Display CI
Write (nout,*) '99 percent Confidence Interval for the estimate'
Write (nout,99998) '(', tl, ' ,', tu, ' )'

99999 Format (1X,A,F7.4)
99998 Format (6X,A,F7.4,A,F7.4,A)
End Program g07abfe
```