Group testing is a procedure in which groups that contain several units (plants) are analysed without having to inspect individual plants, with the purpose of estimating the prevalence of genetically ...modified plants (adventitious presence of unwanted transgenic plants, AP) in a population at a low cost, without losing precision. When pool (group) testing is used to estimate the proportion of AP (p), there are several procedures that can be used for computing the confidence interval (CI); however, they usually do not ensure precision in the estimation of pags This research proposes a formula for determining the required number of pools (g), given a pool size (k), for estimating the proportion of AP plants using the Dorfman model. The proposed formula ensures precision in the estimated proportion of AP because it guarantees that the width (W) of the CI will be equal to, or narrower than, the desired width (v), with a probability of g. This probability accounts for the stochastic nature of the sample variance of pags We give examples to show how to use the proposed sample size formula. Simulated data were created and tables are presented showing the different scenarios that a researcher may encounter. The Monte Carlo method was used to study the coverage and the level of assurance achieved by the proposed sample sizes. An R program that reproduces the results in the tables and makes it easy for the researcher to create other scenarios is given in the Appendix.
Detecting the presence of genetically modified plants (adventitious presence of unwanted transgenic plants, AP) from outcrossing species such as maize requires a method that lowers laboratory costs ...without losing precision. Group testing is a procedure in which groups that contain several units (plants) are analysed without having to inspect individual plants, with the purpose of estimating the prevalence of AP in a population at a low cost without losing precision. When pool (group) testing is used to estimate the prevalence of AP (p), there are sampling procedures for calculating a confidence interval (CI); however, they usually do not ensure precision in the estimation of pags This research proposes a method to determine the number of pools (g), given a pool size (k), that ensures precision in the estimated proportion of AP (that is, it ensures a narrow CI). In addition, the study computes the maximum likelihood estimator of p under pool testing and its exact CI, considering the detection limit of the laboratory, d, and the concentration of AP per unit (c). The proposed sample procedure involves two steps: (1) obtain a sample size that guarantees that the mean width of the CI (w) is narrower than the desired width (v); and (2) iteratively increase the sample size until w is smaller than the desired width (v) with a specified degree of certainty (g). Simulated data were created and tables are presented showing the different possible scenarios that a researcher may encounter. An R program is given and explained that will reproduce the results and make it easy for the researcher to create other scenarios.
A central tenet in a free society is the freedom to choose how to conduct one’s life and manage one’s property, with the responsibility to see that these same freedoms are ensured for others. ...Considerable effort must be expended to enable freedom of choice among a population, particularly in contentious circumstances, and especially in open systems, such as agriculture.
The emergence of conventional agriculture, which relies on the heavy use of synthetic, agrochemical inputs required that concessions/compromises be made, largely by organic farmers, to enable conventional and organic agriculture to co-exist. The advent of genetically modified (GM) crops presents unique co-existence issues, particularly in light of the natural ability of transgenic organisms to hybridize, reproduce, and spread in the environment. Means by which the integrity of organic, conventional and GM farming systems might be assured in order to preserve and ensure farmer and consumer choice is discussed.
An early concern about genetically engineered crops was that transgenes might have undesirable consequences if they ended up in plants and places for which they were not intended. It has been over ...two decades since the first transgenic plants were environmentally released and over a decade since they have been commercialized. It is time to take stock of crop transgenes out of place. I have assembled a selected compilation of 22 incidents of in which crop transgenes were detected in living organisms (seeds or plants) in situations for which they were not intended. Contrary to initial concerns, crop transgenes have rarely introgressed into wild populations, but rather have often ended up in a different variety of the same species. Evolving regulatory policy should heed the large (and increasing) number of well-documented cases of transgenes out-of-place. In particular, it should treat the processed products of transgenic crops differently from living organisms, such as grain, that, if planted, are capable of multiplying their genes.
When detecting the adventitious presence of transgenic plants (AP), it is important to use an appropriate testing method in the laboratory. Dorfman's group testing method is effective for reducing ...the number of laboratory analyses, but does not consider the case where AP is diluted below the sensitivity of the analyses, which causes the rate of false negatives to increase. The objective of this study is to propose binomial and negative binomial probabilistic models for determining the required sample size (n), number of pools (g), and size of the pool (k) for detecting individuals possessing AP with a probability = (1 - a) (for a small a) given: (1) pool size (k); (2) estimated proportion of individuals with AP in the population (p); (3) concentration of the trait of interest (AP) in individual seeds (w); and (4) detection limit of the test (c) (AP concentration in a pool below which it cannot be detected). The proposed models consider the different rates of false positives (d) and false negatives (?), and the assessment of consumer and producer risks. Results have shown that when using the negative binomial, a required sample size n can be determined that guarantees a high probability that m individuals or g pools containing AP will be found. The pools formed have an optimum size, such that one element with AP will be detected at a low cost. The negative binomial distribution should be used when it is known that the proportion of individuals with AP in the population is p < 0.1; thus, it is guaranteed that m individuals or g pools of individuals with AP will be detected with high probability.
