Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia

Fixed sample-size plans for monitoring Plutella xylostella (L.) (Lepidoptera: Plutellidae) on broccoli and other Brassica vegetable crops are popular in Australia for their simplicity and ease of application. But the sample sizes used are often small, ≈10–25 plants per crop, and it may be that they fail to provide sufficient information upon which to base pest control decisions. We tested the performance of seven fixed sample-size plans (10, 15, 20, 30, 35, 40, and 45 plants) by resampling a large data set on P. xylostella in commercial broccoli crops. For each sample size, enumerative and presence-absence plans were assessed. The precision of the plans was assessed in terms of the ratio of the standard error to the mean; and at least 45 and 35 samples were necessary for the enumerative and presence-absence plans, respectively, to attain the generally accepted benchmark of ≤0.3. Sample sizes of 10–20 were highly imprecise. We also assessed the consequences of classifications based on action thresholds (ATs) of 0.2 and 0.8 larvae per plant for the enumerative case, and 0.15 and 0.45 proportion of plants of infested for the presence-absence case. Operating characteristic curves and investigations of the frequency of correct decisions suggest improvements in the performance of plans with increased sample size. In both the enumerative and presence-absence cases, the proportion of incorrect decisions was much higher for the lower of the two ATs assessed, and type II errors (i.e., failure to suggest pest control upon the AT is exceeded) generally accounted for the majority of this error. Type II errors are the most significant from a producer’s standpoint. Further consideration is necessary to determine what is an acceptable type II error rate.

Sample size determination for kernel regression estimation using sequential fixed-width confidence bands

We consider a random design model based on independent and identically distributed pairs of observations (Xi, Yi), where the regression function m(x) is given by m(x) = E(Yi|Xi = x) with one independent variable. In a nonparametric setting the aim is to produce a reasonable approximation to the unknown function m(x) when we have no precise information about the form of the true density, f(x) of X. We describe an estimation procedure of non-parametric regression model at a given point by some appropriately constructed fixed-width (2d) confidence interval with the confidence coefficient of at least 1−. Here, d(> 0) and 2 (0, 1) are two preassigned values. Fixed-width confidence intervals are developed using both Nadaraya-Watson and local linear kernel estimators of nonparametric regression with data-driven bandwidths. The sample size was optimized using the purely and two-stage sequential procedures together with asymptotic properties of the Nadaraya-Watson and local linear estimators. A large scale simulation study was performed to compare their coverage accuracy. The numerical results indicate that the confi dence bands based on the local linear estimator have the better performance than those constructed by using Nadaraya-Watson estimator. However both estimators are shown to have asymptotically correct coverage properties.

The impact of sample size and data quality to classification reliability

The reliability of an induced classifier can be affected by several factors including the data oriented factors and the algorithm oriented factors [3]. In some cases, the reliability could also be affected by knowledge oriented factors. In this chapter, we analyze three special cases to examine the reliability of the discovered knowledge. Our case study results show that (1) in the cases of mining from low quality data, rough classification approach is more reliable than exact approach which in general tolerate to low quality data; (2) Without sufficient large size of the data, the reliability of the discovered knowledge will be decreased accordingly; (3) The reliability of point learning approach could easily be misled by noisy data. It will in most cases generate an unreliable interval and thus affect the reliability of the discovered knowledge. It is also reveals that the inexact field is a good learning strategy that could model the potentials and to improve the discovery reliability.

A simple parametric method for reducing sample sizes in gut passage time trials

Seed dispersal is now regularly analyzed using spatially explicit models, relying in part on frugivore gut passage times to produce model outputs. In determining species-specific gut passage times, there is a trade-off in sample size between minimizing collection effort and maintaining statistical reliability. Here we demonstrate that a two-parameter lognormal parametric distribution reliably fits empirical gut passage time distributions and is easily parameterized using relatively small data sets of approximately 30 defecations. We suggest this approach as a statistically reliable substitute for larger empirical gut passage data sets in seed dispersal modeling, and also as a way of using published gut passage data sets to parameterize new models.

Diet quality in bipolar disorder in a population-based sample of women

Background : Recent epidemiological evidence has indicated a role for diet quality in unipolar depressive illness. This study examined the association between diet quality and bipolar disorder (BD) in an epidemiological cohort of randomly selected, population-based women aged 20–93 years.

Methods : An a priori diet quality score was derived from food frequency questionnaire data, a factor analysis identified habitual dietary patterns and glycemic load was assessed. Mental health was assessed using the SCID-I/NP.

Results : BD was identified in 23 women and there were 691 participants with no history of psychopathology. Compared to those with no psychopathology, those with BD had a higher glycemic load (p = 0.06) and higher scores on a ‘western’ dietary factor (p = 0.03) and the ‘modern’ dietary factor (p = 0.02). For each standard deviation increase in a ‘western’ and ‘modern’ dietary pattern and glycemic load, the odds ratios for BD were increased (‘western’ OR = 1.88, 95% CI 1.33–2.65; ‘modern’ OR = 1.72, 95% CI 1.14–2.39; GL OR = 1.56, 95% CI 1.13–2.14). Conversely, a ‘traditional’ dietary pattern was associated with reduced odds for BD (OR = 0.53 95% CI 0.32–0.89) after adjustments for overall energy intake.

Limitations : The small sample size did not allow for multivariate analyses and the cross-sectional study design precludes any determinations regarding the direction of the relationships between diet quality and BD.

Conclusion : These data are largely concordant with results from dietary studies in unipolar depression. However, clinical recommendations cannot be made until the direction of the relationship between diet quality and BD is determined. Longitudinal studies are warranted.

Maternal 25-hydroxyvitamin D concentration and offspring birth size : effect modification by infant VDR genotype

Background/Objectives: We tested the hypothesis that the relationship between maternal 25-hydroxyvitamin D (25-(OH)D) and offspring birth size differs according to offspring vitamin D receptor (VDR) genotype (Apa1, Bsm1, Fok1 or Taq1).

Subjects/Methods: Mothers of 354 singleton babies had serum 25-(OH)D concentration measured at 28–30 weeks of gestation and consented to measurement of their babies soon after birth. DNA was extracted from the babies’ Guthrie cards.

Results: There was evidence of effect modification by infant FokI genotype. Babies of deficient mothers had lower birth weight with FF or Ff, but not ff genotype (P-value for interaction after adjustment for potential confounding factors=0.02), but thicker subscapular and suprailiac skinfolds with ff, but not FF or Ff genotype (P=0.008 and 0.02, respectively). Sample size was insufficient to investigate effect modification by the other VDR polymorphisms.

Conclusions: These preliminary findings suggest that studies of maternal vitamin D status and birth size may need to take VDR genotype into account.

Size and power properties of structural break unit root tests

In this article, we compare the small sample size and power properties of a newly developed endogenous structural break unit root test of Narayan and Popp (NP, 2010) with the existing two break unit root tests, namely the Lumsdaine and Papell (LP, 1997) and the Lee and Strazicich (LS, 2003) tests. In contrast to the widely used LP and LS tests, the NP test chooses the break date by maximizing the significance of the break dummy coefficient. Using Monte Carlo simulations, we show that the NP test has better size and high power, and identifies the structural breaks accurately. Power and size comparisons of the NP test with the LP and LS tests reveal that the NP test is significantly superior.

Evaluation of neck muscle size: long-term reliability and comparison of methods

Although it is important for prospective studies, the reliability of quantitative measures of cervical muscle size on magnetic resonance imaging is not well established. The aim of the current work was to assess the long-term reliability of measurements of cervical muscle size. In addition, we examined the utility of selecting specific sub-regions of muscles at each vertebral level, averaging between sides of the body, and pooling muscles into larger groups. Axial scans from the base of skull to the third thoracic vertebra were performed in 20 healthy male subjects at baseline and 1.5 years later. We evaluated the semi-spinalis capitis, splenius capitis, spinalis cervicis, longus capitis, longus colli, levator scapulae, sternocleidomastoid, anterior scalenes and middle with posterior scalenes. Bland-Altman analysis showed all measurements to be repeatable between testing-days. Reliability was typically best when entire muscle volume was measured (co-efficients of variation (CVs): 3.3-8.1% depending on muscle). However, when the size of the muscle was assessed at specific vertebral levels, similar measurement precision was achieved (CVs: 2.7-7.6%). A median of 4-6 images were measured at the specific vertebral levels versus 18-37 images for entire muscle volume. This would represent considerable time saving. Based on the findings we also recommend measuring both sides of the body and calculating an average value. Pooling specific muscles into the deep neck flexors (CV: 3.5%) and neck extensors (CV: 2.7%) can serve to reduce variability further. The results of the current study help to establish outcome measures for interventional studies and for sample size estimation.

Influence of vibration resistance training on knee extensor and plantar flexor size, strength, and contractile speed characteristics after 60 days of bed rest

Spaceflight and bed rest (BR) result in loss of muscle mass and strength. This study evaluated the effectiveness of resistance training and vibration-augmented resistance training to preserve thigh (quadriceps femoris) and calf (triceps surae) muscle cross-sectional area (CSA), isometric maximal voluntary contraction (MVC), isometric contractile speed, and neural activation (electromyogram) during 60 days of BR. Male subjects participating in the second Berlin Bed Rest Study underwent BR only [control (CTR), n = 9], BR with resistance training (RE; n = 7), or BR with vibration-augmented resistance training (RVE; n = 7). Training was performed three times per week. Thigh CSA and MVC torque decreased by 13.5 and 21.3%, respectively, for CTR (both P < 0.001), but were preserved for RE and RVE. Calf CSA declined for all groups, but more so (P < 0.001) for CTR (23.8%) than for RE (10.7%) and RVE (11.0%). Loss in calf MVC torque was greater (P < 0.05) for CTR (24.9%) than for RVE (12.3%), but not different from RE (14.8%). Neural activation at MVC remained unchanged in all groups. For indexes related to rate of torque development, countermeasure subjects were pooled into one resistance training group (RT, n = 14). Thigh maximal rate of torque development (MRTD) and contractile impulse remained unaltered for CTR, but MRTD decreased 16% for RT. Calf MRTD remained unaltered for both groups, whereas contractile impulse increased across groups (28.8%), despite suppression in peak electromyogram (12.1%). In conclusion, vibration exposure did not enhance the efficacy of resistance training to preserve thigh and calf neuromuscular function during BR, although sample size issues may have played a role. The exercise regimen maintained thigh size and MVC strength, but promoted a loss in contractile speed. Whereas contractile speed improved for the calf, the exercise regimen only partially preserved calf size and MVC strength. Modification of the exercise regimen seems warranted.

Sensitivity of fine-scale species distribution models to locational uncertainty in occurrence data across multiple sample sizes

To generate realistic predictions, species distribution models require the accurate coregistration of occurrence data with environmental variables. There is a common assumption that species occurrence data are accurately georeferenced; however, this is often not the case. This study investigates whether locational uncertainty and sample size affect the performance and interpretation of fine-scale species distribution models. This study evaluated the effects of locational uncertainty across multiple sample sizes by subsampling and spatially degrading occurrence data. Distribution models were constructed for kelp (Ecklonia radiata), across a large study site (680 km2) off the coast of southeastern Australia. Generalized additive models were used to predict distributions based on fine-resolution (2·5 m cell size) seafloor variables, generated from multibeam echosounder data sets, and occurrence data from underwater towed video. The effects of different levels of locational uncertainty in combination with sample size were evaluated by comparing model performance and predicted distributions. While locational uncertainty was observed to influence some measures of model performance, in general this was small and varied based on the accuracy metric used. However, simulated locational uncertainty caused changes in variable importance and predicted distributions at fine scales, potentially influencing model interpretation. This was most evident with small sample sizes. Results suggested that seemingly high-performing, fine-scale models can be generated from data containing locational uncertainty, although interpreting their predictions can be misleading if the predictions are interpreted at scales similar to the spatial errors. This study demonstrated the need to consider predictions across geographic space rather than performance alone. The findings are important for conservation managers as they highlight the inherent variation in predictions between equally performing distribution models, and the subsequent restrictions on ecological interpretations.

Attending to risk in sequential sampling plans

Researchers typically tackle questions by constructing powerful, highlyreplicated sampling protocols or experimental designs. Such approaches often demand large samples sizes and are usually only conducted on a once-off basis. In contrast, many industries need to continually monitor phenomena such as equipment reliability, water quality, or the abundance of a pest. In such instances, costs and time inherent in sampling preclude the use of highlyintensive methods. Ideally, one wants to collect the absolute minimum number of samples needed to make an appropriate decision. Sequential sampling, wherein the sample size is a function of the results of the sampling process itself, offers a practicable solution. But smaller sample sizes equate to less knowledge about the population, and thus an increased risk of making an incorrect management decision. There are various statistical techniques to account for and measure risk in sequential sampling plans. We illustrate these methods and assess them using examples relating to the management of arthropod pests in commercial crops, but they can be applied to any situation where sequential sampling is used.

Students` perceptions of workshop based introductory macro-economics tutorials: a survey

The declining popularity of Economics courses, evident in the last decade, has fuelled a debate on the nature of Economics units and the way in which they are taught in tertiary institutions. The effectiveness of traditional teaching methods has been questioned as lecturers search for alternative ways of presenting material and engaging students. In recent times, workshop-based/cooperative tutorials have become more popular in promoting deeper learning. This paper assesses the application of such an approach at a large tertiary institution. It evaluates student perceptions of this tutorial method in an Introductory Macroeconomics first-year unit. An anonymous questionnaire was used. Whilst the sample size is small (n = 56), the results are important in that this is the first such study in Macroeconomics. Students found workshop-based tutorials useful, preferred them over lecture style tutorials, and found that they fostered inclusivity. The importance of tutorials per se, is reiterated. Students state that tutorials are an important adjunct to lectures. This study also looks at students' study habits: finding that on average they spend less than one hour per week studying Economics and most prepare only occasionally for tutorials. The sample studied indicates that there are notable differences in the perceptions of tutorials and teaching methods between the genders and between local and international students. This may impact on the way in which tutorials are conducted effectively.

Mortality, malnutrition and the humanitarian response to the food crises in Lesotho

Background: At the height of the food crisis in southern Africa, the Government of Lesotho declared a state of famine and emergency in April 2002 and launched a Famine Relief Appeal for over $137 million. World Vision, in partnership with the World Food Program, became involved in December 2002 providing food aid to affected communities.
Objective: to document mortality rates, causes of death, malnutrition prevalence, and the proportion of lost pregnancies after almost three years of humanitarian response to the food crisis in Lesotho and to propose a way forward.
Design: A two-stage, 30 cluster household survey was undertaken in three districts from the 16th to the 26th of May 2005, with a sample size of 3610 people.
Results: The crude mortality rate (CMR) of 0.8/10,000/day (95%CI: 0.7-0.9). The reported CMR was significantly lower than the CMR emergency threshold (<1/10,000/day). Using 2000 as a pre-drought baseline, 38528 excess deaths occurred between 2000 and 2005. The under-five mortality rate (U5MR) of 3.2 deaths/10,000/day (95%CI: 2.8-3.6/10,000/day) was 4 times the reported CMR and 1.4 times higher the U5MR emergency threshold for sub-Saharan Africa (2.3/10,000/day). CMR was lower among food aid beneficiaries (0.68; 95%CI: 0.57-0.79) than non-beneficiaries (1.42; 95%CI: 1.13-1.70). This was also true for U5MR (2.94; 95%CI: 2.39-3.50 versus 6.44; 95%CI: 5.21-7.68). The prevalence of wasting increased from 5.4% to 12% while that of stunting declined from 45.4% to 36.2% between 2000 and 2005, but the nutritional status did not vary by beneficiary status.
Conclusion: Despite the alarming U5MR, findings suggest that the food aid program ensured survival mainly among adults. The situation could have been catastrophic in the absence of humanitarian assistance.

Testosterone replacement therapy-perceptions of recipients and partners

Background. The androgenic hormones are important determinants of sexual behaviour in men. Testosterone replacement is important treatment for pituitary disease to maintain normal functioning. Although the physical effects of testosterone replacement have been well documented, little is known about the effects on relationships, particularly from the point of view of the sexual partners of men receiving testosterone replacement.

Aims. This paper reports a study exploring the perceptions of testosterone replacement on well-being and sexual functioning.

Methods. Semi-structured interviews were conducted with five men receiving testosterone implants (recipients), their permanent partners, and five recipients without partners. Recipient serum testosterone concentration was measured at 0, 1 and 4 months after testosterone implantation.

Results. The three groups reported similar effects of testosterone on well-being and sexual functioning. Recipient and partner ratings were also similar. Strength was less affected by decreasing testosterone concentration than energy in men with partners, but both strength and energy declined in men without partners. Decreased testosterone levels had a statistically significantly different effect on libido at time zero between men with and without partners (P < 0·015) and on ability to sustain an erection, but the ability to achieve an erection persisted over the 6 months in both male groups. Intercourse frequency increased from once per week at time 0 to ≥3 per week between 1 and 4 months after implant in men with partners. There were important effects of testosterone deficiency on general and sexual relationships, and these differed between men with partners and those without.

Conclusions. Testosterone has important physical and psychological benefits that may be related to the age at which testosterone replacement commences and the indications for its use. The small sample size may limit the ability to generalize the findings outside the study.