Rs. Atlas et al., COMPUTER-SIMULATION OF ALTERNATIVE SAMPLING STRATEGIES TO ESTIMATE RISK OF INFECTION FROM CRYPTOSPORIDIUM, Computers in biology and medicine, 23(4), 1993, pp. 283-294
Estimation of acceptably safe levels of biological contaminants in dri
nking water requires fitting a mathematical model to infection rates o
bserved in small samples of human subjects. Because of obvious constra
ints on exposing human subjects to infective conditions, it is not fea
sible to compare the utilities of alternative sampling strategies and
research designs using data from real experiments. Computer simulation
methods were used to generate sample data having known probabilities
of infection determined by an exponential or log-linear infectivity mo
del. Experimental conditions that were examined included variations in
the total available sample size, strategies for allocating subjects a
mong different test concentrations, and methods for fitting a predicti
on model to the observed data. Results confirmed that data obtained by
exposing most subjects to a concentration that produces an infection
rate approximating 50% and calculating the sample regression coefficie
nt for the log-linear model as the average infectivity-to-concentratio
n ratio provided the best estimates of safe concentration. Exposing a
single subject to each successively higher test level until an initial
infection is observed, and exposing all remaining subjects at that le
vel, or an adjacent log-concentration level is a tactic supported by t
he empirical results.