p {msamp}

Calculate the probability of a single sample being contaminated

Description

The p() function calculates the probability of a single sample unit, with weight w, and postulated contamination, C, being contaminated above a target level, G.

Usage

p(
  C,
  w,
  G,
  Sens,
  D = c("homogeneous", "heterogeneous", "localized"),
  r = NULL,
  f = NULL
)

Arguments

C

suspected lot contamination (CFU/g)

w

weight of single sample unit (g)

G

target value to detect (CFU/g)

Sens

sensitivity of the analytical test (%)

D

distribution of the bacteria in the product lot: "homogeneous", "heterogeneous", or "localized"

r

for the heterogeneous case only, the degree of heterogeneity. r > 0

f

for the localized case, r is further specified. 0 < f < 1

Details

Refer to vignette for details.

Value

A numeric value: the probability of a single sample unit being contaminated above target level.

Examples

#A sample of 25 grams (w=25) is collected and analyzed using an analytical
#test with sensitivity of 90% (Sens=.9), to detect at least 5 CFU's/g (G=5).
#The suspected or postulated level of contamination in the lot is 4 CFU's/g (C=4)

#homogeneous case
p(C=4,w=25,G=5,Sens=.9,D="homogeneous",r=NULL,f=NULL)
# 0.006117884
#heterogeneous case-- dispersion, r, is postulated as 2
p(C=4,w=25,G=5,Sens=.9,D="heterogeneous",r=2,f=NULL)
# 0.2576463
#localized case -- 30% of the lot is postulated to be contaminated
p(C=4,w=25,G=5,Sens=.9,D="localized",r=NULL,f=.3)
# 0.001835365