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The group testing procedure divides sampled units into several groups, and then obtains an overall test result for each group. It is used to identify specific individuals who have a given attribute, or to estimate the overall prevalence of the attribute in the population. We here investigate how group retesting can improve precision of estimation and its cost-efficiency, which are important considerations for investigators. Retesting uses two or more group stages, with repeat testing of the original samples at each stage. Previous authors have proposed a procedure with two stages having equal group sizes, and where the number of groups tested at the second stage is based on the number of positive groups in the first stage. In this paper, our main focus is on estimating the prevalence p of affected individuals in a population, and identifying cost-efficient experimental designs, when using two-stage testing with unequal group sizes at each stage. We use analytical solutions for the precision of estimation, together with simulations to evaluate various experimental designs. We consider the value of retesting at the second stage, and determine when using only one stage of testing might be sufficiently precise. [ABSTRACT FROM AUTHOR]

When estimating a proportion p by group testing, and it is desired to increase precision, it is sometimes impractical to obtain additional individuals but it is possible to retest groups formed from the individuals within the groups that test positive at the first stage. Hepworth and Watson assessed four methods of retesting, and recommended a random regrouping of individuals from the first stage. They developed an estimator of p for their proposed method, and, because of the analytic complexity, used simulation to examine its variance properties. We now provide an analytical solution to the variance of the estimator, and compare its performance with the earlier simulated results. We show that our solution gives an acceptable approximation in a reasonable range of circumstances. [ABSTRACT FROM AUTHOR]

In the estimation of a proportion p by group testing (pooled testing), retesting of units within positive groups has received little attention due to the minimal gain in precision compared to testing additional units. If acquisition of additional units is impractical or too expensive, and testing is not destructive, we show that retesting can be a useful option. We propose the retesting of a random grouping of units from positive groups, and compare it with nested halving procedures suggested by others. We develop an estimator of p for our proposed method, and examine its variance properties. Using simulation we compare retesting methods across a range of group testing situations, and show that for most realistic scenarios, our method is more efficient. [ABSTRACT FROM AUTHOR]

Understanding the roles of different types of natural and artificial wetlands in providing habitat for waterbirds is crucial to active interventions to conserve wetland biodiversity. This study made use of a large database compiled over 22 years from the 'Summer Waterfowl Count' to determine the relative use of five wetland types by 18 species of waterfowl in Victoria, south-eastern Australia. The abundance of 14 species and density of 15 differed significantly (P < 0.05) according to wetland type. Waste stabilisation ponds supported significantly higher abundances and densities of many species, a greater number of species and a community structure that was markedly different from the other wetland types. Based on the findings of this study, we believe that the unique characteristics of each wetland type warrant the conservation of each. Moreover, waste stabilisation ponds are significant refugia for waterfowl in Victoria and the trend to modernise sewage treatment plants, to the detriment of waterfowl, should be approached with caution. It is suggested that these findings are probably applicable in other parts of the world, although further research is needed to confirm their universal application. [ABSTRACT FROM AUTHOR]

Although it is known that immature composts can depress plant growth, few studies have quantified this effect in real-world scenarios with field-grown crops. Glasshouse and field trials were used to investigate the effect of maturation of grease trap compost (GTC) on plant growth. Grease trap waste was composted for 7-14 d in an in-vessel reactor with shredded green waste, sawdust and chicken manure and matured in windrows for up to 6 weeks. In the glasshouse trial, compost samples were mixed with an equal volume of coarse sand and were compared with a standard mix of 3 parts composted pine bark to I part coarse sand (v/v). In these trials, fresh GTC suppressed germination and growth of both radish and alyssum compared to the standard mix. Two weeks maturation reduced phytotoxicity of GTC but it was still phytotoxic relative to the standard mix. After 6 weeks maturation, GTC performed as well as the standard mix in all measures of plant growth and germination except for plant height of alyssum. Fresh and mature GTC were also used as soil conditioners in field trials on a commercial vegetable farm in the Werribee irrigation district, Victoria, Australia. Treatments consisted of GTC at 5 or 10 t ha-1, nil compost or a pelletised poultry manure product (Zest®) at 618 kg ha-1 arranged in a factorial design with 100% and 75% of the grower's standard fertilizer rate (741 kg ha-1 Rustica-Plus®). Head weight of lettuce was significantly reduced (by up to 18%) by the application of 10 t ha-1 of fresh GTC at the grower's standard fertiliser rate. When the fertiliser rate was reduced to 75%, the negative impact of fresh GTC was less apparent. In contrast to the first crop, the performance of mature GTC compared to the controls was independent of fertilizer rate (soil amendment x fertilizer interaction not significant at p<0.05). Application of 5 and 10 t ha-1 of mature GTC increased head weight of lettuce by 11% and 12% respectively compared to the control plus Zest® treatment. This research highlights the need of a better understanding of the maturity requirements of composts for use as soil amendments and growing media in horticultural production. [ABSTRACT FROM AUTHOR]