False Positive Error Rate Research Articles

Real-time detection of faecally contaminated drinking water with tryptophan-like fluorescence: defining threshold values

We assess the use of fluorescent dissolved organic matter at excitation-emission wavelengths of 280nm and 360nm, termed tryptophan-like fluorescence (TLF), as an indicator of faecally contaminated drinking water. A significant logistic regression model was developed using TLF as a predictor of thermotolerant coliforms (TTCs) using data from groundwater- and surface water-derived drinking water sources in India, Malawi, South Africa and Zambia. A TLF threshold of 1.3ppb dissolved tryptophan was selected to classify TTC contamination. Validation of the TLF threshold indicated a false-negative error rate of 15% and a false-positive error rate of 18%. The threshold was unsuccessful at classifying contaminated sources containing <10 TTC cfu per 100mL, which we consider the current limit of detection. If only sources above this limit were classified, the false-negative error rate was very low at 4%. TLF intensity was very strongly correlated with TTC concentration (ρs=0.80). A higher threshold of 6.9ppb dissolved tryptophan is proposed to indicate heavily contaminated sources (≥100 TTC cfu per 100mL). Current commercially available fluorimeters are easy-to-use, suitable for use online and in remote environments, require neither reagents nor consumables, and crucially provide an instantaneous reading. TLF measurements are not appreciably impaired by common intereferents, such as pH, turbidity and temperature, within typical natural ranges. The technology is a viable option for the real-time screening of faecally contaminated drinking water globally.

Laboratory tests for identification or exclusion of heparin induced thrombocytopenia: HIT or miss?

Heparin induced thrombocytopenia (HIT) is a potentially fatal condition that arises subsequent to formation of antibodies against complexes containing heparin, usually platelet-factor 4-heparin ("anti-PF4-heparin"). Assessment for HIT involves both clinical evaluation and, if indicated, laboratory testing for confirmation or exclusion, typically using an initial immunological assay ("screening"), and only if positive, a secondary functional assay for confirmation. Many different immunological and functional assays have been developed. The most common contemporary immunological assays comprise enzyme-linked immunosorbent assay [ELISA], chemiluminescence, lateral flow, and particle gel techniques. The most common functional assays measure platelet aggregation or platelet activation events (e.g., serotonin release assay; heparin-induced platelet activation (HIPA); flow cytometry). All assays have some sensitivity and specificity to HIT antibodies, but differ in terms of relative sensitivity and specificity for pathological HIT, as well as false negative and false positive error rate. This brief article overviews the different available laboratory methods, as well as providing a suggested approach to diagnosis or exclusion of HIT.

Use of the Rey 15-Item Test as a performance validity test in an elderly population

ABSTRACTThe objective of this study was to determine the effectiveness of the Rey 15-Item Test in elderly individuals with and without cognitive impairment and to develop new indices to function with this population, if needed. The sample consisted of 185 individuals referred for outpatient neuropsychological evaluation. All were clinically evaluated and administered the Rey 15-Item Test (RFIT) with recognition as part of this procedure. Significant differences were present between those passing and failing the RFIT on referral question; working status; age; and diagnosis of cognitive impairment. Individuals age 60+ failed the test at rates in excess of 35%. Diagnosis also played a role with those with more severe cognitive diagnosis failing at higher rates; even in those with no diagnosis, however, 19% of elderly individuals did not produce a passing score. The extant cutoff scores commonly used with the RFIT produce unacceptably high false positive error rates to be a useful freestanding Performance Validity Test (PVT) with individuals above age 59. The introduction of a new combination score and use of rare scores and patterns of scores improves the psychometric properties of the RFIT when used with elderly adults. Cautious use of PVTs is warranted until they have been validated with aged populations.

Challenges in confirming eradication success of invasive red-eared sliders

Confirming eradication success can be notoriously difficult and costly, especially when the species is still present but remains undetected, due to very low population densities and imperfect detection methods. There has been a lack of research on appropriate guidelines and estimation procedures for declaring eradication success for programs aimed at eradicating alien reptiles. Here we develop quantitative rules for confirmation monitoring in eradication campaigns of the red-eared slider turtle (Trachemys scripta elegans). We used a database of slider trapping data from control and eradication campaigns conducted in localities across the Iberian Peninsula and southern France to construct models for inferring appropriate trapping efforts for confirming slider turtle eradication. Basking traps were slightly more efficient than net traps in capturing sliders, although trapping was an inefficient monitoring method given the low capture probabilities estimated. The results of our spatially-explicit eradication scenarios revealed the importance of habitat configuration in declaring eradication success. Declaration of eradication success is contingent on the thresholds set to minimise false positives (i.e., falsely declaring eradication successful), but in any scenario large trapping efforts were required to confirm eradication. Given the low estimated capture probabilities, alternative methods such as eDNA and visual surveys should be considered for monitoring sliders. We suggest that if the costs associated with the impact of alien sliders can be adequately estimated, then eradication can be confirmed by rules minimising both false positive and negative error rates. Otherwise, rules minimising false positive errors would be more appropriate.

Power analysis for RNA-Seq differential expression studies

BackgroundSample size calculation and power estimation are essential components of experimental designs in biomedical research. It is very challenging to estimate power for RNA-Seq differential expression under complex experimental designs. Moreover, the dependency among genes should be taken into account in order to obtain accurate results.ResultsIn this paper, we propose a simulation based procedure for power estimation using the negative binomial distribution and assuming a generalized linear model (at the gene level) that considers the dependence between gene expression level and its variance (dispersion) and also allows equal or unequal dispersion across conditions. We compared the performance of both Wald test and likelihood ratio test under different scenarios. The null distribution of the test statistics was simulated for the desired false positive control to avoid excess false positives with the usage of an asymptotic chi-square distribution. We applied this method to the TCGA breast cancer data set.ConclusionsWe provide a framework for power estimation of RNA-Seq data. The proposed procedure is able to properly control the false positive error rate at the nominal level.

Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) processing speed scores as measures of noncredible responding: The third generation of embedded performance validity indicators.

Research suggests that select processing speed measures can also serve as embedded validity indicators (EVIs). The present study examined the diagnostic utility of Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) subtests as EVIs in a mixed clinical sample of 205 patients medically referred for neuropsychological assessment (53.3% female, mean age = 45.1). Classification accuracy was calculated against 3 composite measures of performance validity as criterion variables. A PSI ≤79 produced a good combination of sensitivity (.23-.56) and specificity (.92-.98). A Coding scaled score ≤5 resulted in good specificity (.94-1.00), but low and variable sensitivity (.04-.28). A Symbol Search scaled score ≤6 achieved a good balance between sensitivity (.38-.64) and specificity (.88-.93). A Coding-Symbol Search scaled score difference ≥5 produced adequate specificity (.89-.91) but consistently low sensitivity (.08-.12). A 2-tailed cutoff on the Coding/Symbol Search raw score ratio (≤1.41 or ≥3.57) produced acceptable specificity (.87-.93), but low sensitivity (.15-.24). Failing ≥2 of these EVIs produced variable specificity (.81-.93) and sensitivity (.31-.59). Failing ≥3 of these EVIs stabilized specificity (.89-.94) at a small cost to sensitivity (.23-.53). Results suggest that processing speed based EVIs have the potential to provide a cost-effective and expedient method for evaluating the validity of cognitive data. Given their generally low and variable sensitivity, however, they should not be used in isolation to determine the credibility of a given response set. They also produced unacceptably high rates of false positive errors in patients with moderate-to-severe head injury. Combining evidence from multiple EVIs has the potential to improve overall classification accuracy. (PsycINFO Database Record

Long Fragment Read (LFR) Technology: Cost-Effective, High-Quality Genome-Wide Molecular Haplotyping.

In this chapter, we describe Long Fragment Read (LFR) technology, a DNA preprocessing method for genome-wide haplotyping by whole genome sequencing (WGS). The addition of LFR prior to WGS on any high-throughput DNA sequencer (e.g., Complete Genomics Revolocity™, BGISEQ-500, Illumina HiSeq, etc.) enables the assignment of single-nucleotide polymorphisms (SNPs) and other genomic variants onto contigs representing contiguous DNA from a single parent (haplotypes) with N50 lengths of up to ~1 Mb. Importantly, this is achieved independent of any parental sequencing data or knowledge of parental haplotypes. Further, the nature of this method allows for the correction of most amplification, sequencing, and mapping errors, resulting in false-positive error rates as low as 10-9. This method can be employed either manually using hand-held micropipettors or in the preferred, automated manner described below, utilizing liquid-handling robots capable of pipetting in the nanoliter range. Automating the method limits the amount of hands-on time and allows significant reduction in reaction volumes. Further, the cost of LFR, as described in this chapter, is moderate, while it adds invaluable whole genome haplotype data to almost any WGS process.

Evaluation of a Myopic Normative Database for Analysis of Retinal Nerve Fiber Layer Thickness.

Analysis of retinal nerve fiber layer (RNFL) abnormalities with optical coherence tomography in eyes with high myopia has been complicated by high rates of false-positive errors. An understanding of whether the application of a myopic normative database can improve the specificity for detection of RNFL abnormalities in eyes with high myopia is relevant. To evaluate the diagnostic performance of a myopic normative database for detection of RNFL abnormalities in eyes with high myopia (spherical equivalent, -6.0 diopters [D] or less). In this cross-sectional study, 180 eyes with high myopia (mean [SD] spherical equivalent, -8.0 [1.8] D) from 180 healthy individuals were included in the myopic normative database. Another 46 eyes with high myopia from healthy individuals (mean [SD] spherical equivalent, -8.1 [1.8] D) and 74 eyes from patients with high myopia and glaucoma (mean [SD] spherical equivalent, -8.3 [1.9] D) were included for evaluation of specificity and sensitivity. The 95th and 99th percentiles of the mean and clock-hour circumpapillary RNFL thicknesses and the individual superpixel thicknesses of the RNFL thickness map measured by spectral-domain optical coherence tomography were calculated from the 180 eyes with high myopia. Participants were recruited from January 2, 2013, to December 30, 2015. The following 6 criteria of RNFL abnormalities were examined: (1) mean circumpapillary RNFL thickness below the lower 95th or (2) the lower 99th percentile; (3) one clock-hour or more for RNFL thickness below the lower 95th or (4) the lower 99th percentile; and (5) twenty contiguous superpixels or more of RNFL thickness in the RNFL thickness map below the lower 95th or (6) the lower 99th percentile. Specificities and sensitivities for detection of RNFL abnormalities. Of the 46 healthy eyes and 74 eyes with glaucoma studied (from 39 men and 38 women), the myopic normative database showed a higher specificity (63.0%-100%) than did the built-in normative database of the optical coherence tomography instrument (8.7%-87.0%) for detection of RNFL abnormalities across all the criteria examined (differences in specificities between 13.0% [95% CI, 1.1%-24.9%; P = .01] and 54.3% [95% CI, 37.8%-70.9%; P < .001]) except for the criterion of mean RNFL thickness below the lower 99th percentile, in which both normative databases had the same specificities (100%) but the myopic normative database exhibited a higher sensitivity (71.6% vs 86.5%; difference in sensitivities, 14.9% [95% CI, 4.6%-25.1%; P = .002]). The application of a myopic normative database improved the specificity without compromising the sensitivity compared with the optical coherence tomography instrument's built-in normative database for detection of RNFL abnormalities in eyes with high myopia. Inclusion of myopic normative databases should be considered in optical coherence tomography instruments.

Pre-implantation genetic testing in ART: who will benefit and what is the evidence?

Pre-implantation genetic diagnosis for aneuploidy testing (PGD-A) is a tool to identify euploid embryos during IVF. The suggested populations of patients that can benefit from it are infertile women of advanced maternal age, with a history of recurrent miscarriages and/or IVF failures. However, a general consensus has not yet been reached.After the clinical failure of its first version based on cleavage stage biopsy and 9 chromosome-FISH analysis, PGD-A is currently performed by 24 chromosome screening techniques on trophectoderm (TE) biopsies. This approach has been clearly demonstrated to involve a higher clinical efficiency with respect to the standard care, in terms of sustained pregnancy rate per transfer and lower miscarriage rate. However, data about PGD-A efficacy calculated on a per intention-to-treat basis, as well as an analysis of its cost-effectiveness, are still missing.TE biopsy is a safe and extensively validated approach with low biological and technical margin of error. Firstly, the prevalence of mosaic diploid/aneuploid blastocysts is estimated to be between 0 and 16 %, thus largely tolerable. Secondly, all the comprehensive chromosome screening (CCS) technologies adapted to, or designed to conduct PGD-A are highly concordant, and qPCR in particular has been proven to show the lowest false positive error rate (0.5 %) and a clinically recognizable error rate per blastocyst of just 0.21 %.In conclusion, there is a sufficient body of evidence to support the clinical application of CCS-based PGD-A on TE biopsies. The main limiting factor is the need for a high-standard laboratory to conduct blastocyst culture, biopsy and vitrification without impacting embryo viability.

Intuitive Error Rate Estimates for the Forensic Sciences

There is a risk of error associated with all forensic science conclusions. However, no proper studies have been conducted in any of the forensic sciences to estimate the rate at which forensic science conclusions are wrong. As a result, jurors and other consumers of forensic science information are left to speculate about what those error rates might be. The present paper provides data from an online study (n = 210) about what jury-eligible people (“jurors”) think the false positive error rates are for five types of forensic science evidence (DNA, fingerprints, bite marks, microscopic hair, and handwriting). Jurors’ median estimates range from a high of 1 in 100,000 (handwriting) to a low of 1 in 1,000,000,000 (DNA). The significance of these estimated false positive error rates is discussed.

Comparison of Three Visual Field Tests in Children: Frequency Doubling Test, 24-2 and 30-2 SITA Perimetry

ABSTRACTBackground: To investigate the reliability of FDT and 24-2 and 30-2 Humphrey perimetry in children. Methods: We retrospectively reviewed the records corresponding to 274 eyes of children aged 6–12 years, who underwent FDT and 30-2 and 24-2 Humphrey visual field testing from January 2011 through March 2013. Each test group was divided into two subgroups: a normal visual acuity subgroup (> 0.8 Snellen, group 1) and a low visual acuity subgroup (≤0.8 Snellen, group 2). Reliability indexes such as fixation losses, test duration, and the number and rate of false-positive errors were analyzed. Results: In both subgroups, test duration was shortest for 24-2 perimetry (group 1: p < 0.0001; group 2: p < 0.0001). FDT was associated with lower rates of fixation loss, false positive errors, and false negative errors than 30-2 perimetry. However, the fixation loss rate of FDT was only significantly lower under the subgroup analysis. The normal visual acuity subgroup had a higher MD score on FDT vs. 30-2 perimetry (P = 0.028). However, the PSD was similar for all tests. Conclusion: This reliability study showed that FDT perimetry is superior to 30-2 SITA perimetry. There was no significant difference in the reliability indexes for FDT and 24-2 SITA perimetry; thus, when considering test duration and reliability, 24-2 SITA perimetry appears to be the optimal choice in pediatric patients.

Near-infrared spectroscopy for detection of hailstorm damage on olive fruit

A rapid, robust, and economical method to detect hailstorm-damaged olive fruit (Olea europaea L.) would benefit both consumers and producers of olives and olive oil. Here, the feasibility of using Near-Infrared (NIR) spectroscopy for olive fruit sorting (cv. Canino) into hailstorm-damaged and undamaged classes is demonstrated. Features selected from the entire spectra by the genetic algorithm (two to six features per model) were input to Linear Discriminant Analysis, Quadratic Discriminant Analysis and k-Nearest Neighbor routines to develop models to classify olive fruit. Spectral pretreatment and feature selection were optimized through an iterative routine developed in R statistical software. Each model was evaluated based on false positive (α-error), false negative (β-error) and total error rates. The most accurate models yielded total error rates of less than five percent. The optimal features corresponded to R[1320nm], R[∼1460nm], R[∼1650nm], R[∼1920nm], R[∼2080nm], R[∼2200nm] and R[∼2220nm], where R[x] represents the reflectance of light from the sample at a wavelength of x nm. The results indicate that single-point NIR spectroscopy is a feasible basis for hailstorm damage detection in olive fruit with the potential to allow on-line implementation on milling production lines.

Certifying Equality With Limited Interaction

The equality problem is usually one's first encounter with communication complexity and is one of the most fundamental problems in the field. Although its deterministic and randomized communication complexity were settled decades ago, we find several new things to say about the problem by focusing on three subtle aspects. The first is to consider the expected communication cost (at a worst-case input) for a protocol that uses limited interaction--i.e., a bounded number of rounds of communication--and whose error probability is zero or close to it. The second is to treat the false negative error rate separately from the false positive error rate. The third is to consider the information cost of such protocols. We obtain asymptotically optimal rounds-versus-cost tradeoffs for equality: both expected communication complexity and information complexity scale as $$\Theta ({{\mathrm{ilog}}}^{r-1} n)$$ź(ilogr-1n), where r is the number of rounds and $${{\mathrm{ilog}}}^k n = \log \log \cdots \log n$$ilogkn=loglogźlogn, with k logs. These bounds hold even when the false negative rate approaches 1. For the case of zero-error communication cost, we obtain essentially matching bounds, up to a tiny additive constant. We also provide some applications. As an application of our information cost bounds, we obtain new bounded-round randomized lower bounds for the Intersection problem, in which there are two players who hold subsets $$S,T \subseteq [n]$$S,T⊆[n]. In many realistic scenarios, the sizes of S and T are significantly smaller than n, so we impose the constraint that $$|S|, |T| \le k$$|S|,|T|≤k. We study the minimum number of bits the parties need to communicate in order to compute the entire intersection set $$S \cap T$$SźT, using r rounds. We show that any r-round protocol has information cost (and thus communication cost) $$\Omega (k {{\mathrm{ilog}}}^r k)$$Ω(kilogrk) bits. We also give an O(r)-round protocol achieving $$O(k{{\mathrm{ilog}}}^r k)$$O(kilogrk) bits, which for $$r = \log ^* k$$r=logźk gives a protocol with O(k) bits of communication. This is in contrast to other basic problems such as computing the union or symmetric difference, for which $$\Omega (k\log (n/k))$$Ω(klog(n/k)) bits of communication is required for any number of rounds.

False-Positive Error Rates for Reliable Digit Span and Auditory Verbal Learning Test Performance Validity Measures in Amnestic Mild Cognitive Impairment and Early Alzheimer Disease

The objective is to examine failure on three embedded performance validity tests [Reliable Digit Span (RDS), Auditory Verbal Learning Test (AVLT) logistic regression, and AVLT recognition memory] in early Alzheimer disease (AD; n = 178), amnestic mild cognitive impairment (MCI; n = 365), and cognitively intact age-matched controls (n = 206). Neuropsychological tests scores were obtained from subjects participating in the Alzheimer's Disease Neuroimaging Initiative (ADNI). RDS failure using a ≤7 RDS threshold was 60/178 (34%) for early AD, 52/365 (14%) for MCI, and 17/206 (8%) for controls. A ≤6 RDS criterion reduced this rate to 24/178 (13%) for early AD, 15/365 (4%) for MCI, and 7/206 (3%) for controls. AVLT logistic regression probability of ≥.76 yielded unacceptably high false-positive rates in both clinical groups [early AD = 149/178 (79%); MCI = 159/365 (44%)] but not cognitively intact controls (13/206, 6%). AVLT recognition criterion of ≤9/15 classified 125/178 (70%) of early AD, 155/365 (42%) of MCI, and 18/206 (9%) of control scores as invalid, which decreased to 66/178 (37%) for early AD, 46/365 (13%) for MCI, and 10/206 (5%) for controls when applying a ≤5/15 criterion. Despite high false-positive rates across individual measures and thresholds, combining RDS ≤ 6 and AVLT recognition ≤9/15 classified only 9/178 (5%) of early AD and 4/365 (1%) of MCI patients as invalid performers. Embedded validity cutoffs derived from mixed clinical groups produce unacceptably high false-positive rates in MCI and early AD. Combining embedded PVT indicators lowers the false-positive rate.

Normative comparisons for large neuropsychological test batteries: User-friendly and sensitive solutions to minimize familywise false positives

ABSTRACTIntroduction. In neuropsychological research and clinical practice, a large battery of tests is often administered to determine whether an individual deviates from the norm. We formulate three criteria for such large battery normative comparisons. First, familywise false-positive error rate (i.e., the complement of specificity) should be controlled at, or below, a prespecified level. Second, sensitivity to detect genuine deviations from the norm should be high. Third, the comparisons should be easy enough for routine application, not only in research, but also in clinical practice. Here we show that these criteria are satisfied for current procedures used to assess an overall deviation from the norm—that is, a deviation given all test results. However, we also show that these criteria are not satisfied for current procedures used to assess test-specific deviations, which are required, for example, to investigate dissociations in a test profile. We therefore propose several new procedures to assess such test-specific deviations. These new procedures are expected to satisfy all three criteria. Method. In Monte Carlo simulations and in an applied example pertaining to Parkinson disease, we compare current procedures to assess test-specific deviations (uncorrected and Bonferroni normative comparisons) to new procedures (Holm, one-step resampling, and step-down resampling normative comparisons). Results. The new procedures are shown to: (a) control familywise false-positive error rate, whereas uncorrected comparisons do not; (b) have higher sensitivity than Bonferroni corrected comparisons, where especially step-down resampling is favorable in this respect; (c) be user-friendly as they are implemented in a user-friendly normative comparisons website, and as the required normative data are provided by a database. Conclusion. These new normative comparisons procedures, especially step-down resampling, are valuable additional tools to assess test-specific deviations from the norm in large test batteries.

Deriving nutrient criteria to minimize false positive and false negative water use impairment determinations

ABSTRACTSmeltzer E, Kamman NC, Fiske S. 2016. Deriving nutrient criteria to minimize false positive and false negative water use impairment determinations. Lake Reserv Manage. 32:182–193.Nutrient water quality criteria for lakes and wadeable streams in Vermont were derived using receiver operating characteristic (ROC) analysis to evaluate false positive and false negative error rates in making water use impairment determinations. Numeric nutrient criteria for total phosphorus (TP), chlorophyll a (Chl-a), and Secchi depth were derived to protect aesthetic uses in lakes in a manner that balanced and minimized these 2 types of errors. TP and total nitrogen (TN) criteria were derived to protect aquatic life uses in wadeable streams. The resulting criteria for lakes were TP = 17−18 µg/L, Chl-a = 3.8−5.2 µg/L, and Secchi depth = 2.6−3.2 m, depending on the applicable tiered water use objective defined in the state's water quality standards. Wadeable stream criteria were TP = 9−27 µg/L and TN = 0.25−1.3 mg/L, depending on the designated water use and the stream macroinvertebrate community type. These criteria, with some modifications and with the exception of TN, were incorporated into the Vermont Water Quality Standards as part of an integrated nutrient criteria framework.

Investigations of molecular evolutionary mechanisms in partially sequenced heat shock protein70 homologue-coding gene of Oliveleaf yellowing-associated virus isolates from Tunisia

Abstract Reverse Transcription Polymerase Chain Reaction (RT-PCR) using new designed primers pair for Heat Shock Protein70 homologue (HSP70h) of Olive leaf yellowing-associated virus revealed 667 amplified product of 10 olive accessions collected from various olive-growing regions in Tunisia. Amplicons were cloned and sequenced. The sequences were deposited in the international databases. Pairwise sequence comparisons among 10 Tunisian isolates along with a reference sequence (AJ440010) extracted from GenBank revealed a nucleotide identity of 86.06-99.40 and an amino acid similarity of 91.89-99.55. Sequence multiple alignments were searched for evidence of recombination using three methods, ie. Differences of Sums of Squares (DSS) implemented in TOPALi v2.5 software and Single Breakpoint (SBP) along with GARD, a genetic algorithm, both incorporated in HyPhy package. All used methods pointed out the presence of putative breaking points in partially sequenced HSP70h-coding gene. Since failing to account for recombination can mislead the phylogeny inference and can elevate the false positive error rate in positive selection assessment, the use of GARD resulted in the reconstruction of different phylogenies on the left as well as on the right sides of putative recombination breaking points, and the 11 accessions were distributed into at least three clusters compared to MEGA6 software which delineated only two clades. Nonetheless, by dividing the aligned sequences at breakpoints into separate sequence sets, MEGA6 delineated a clustering pattern different from the former two. As a result, recombination reshuffled the affiliation of the different accessions to the clusters. Analysis of selection pressures exerted on HSP70h encoded protein using different models (SLAC, IFEL, FEL, REL, PARRIS, FUBAR, MEME, GA Branch, and PRIME) taking into account recombination, and implemented in HyPhy package, revealed that it underwent predominantly purifying selection as confirmed by Tajima’s D, Fu and Li’s D and F tests, and SNAP algorithm. However, a few sites were also under positive selection as assessed by various models such as FEL, IFEL, REL, MEME, and PRIME.

Liana canopy cover mapped throughout a tropical forest with high-fidelity imaging spectroscopy

Abstract Increasing size and abundance of lianas relative to trees are pervasive changes in Neotropical forests that may lead to reduced forest carbon stocks. Yet the liana growth form is chronically understudied in large-scale tropical forest censuses, resulting in few data on the scale, cause, and impact of increasing lianas. Satellite and airborne remote sensing provide potential tools to map and monitor lianas at much larger spatial and rapid temporal scales than are possible with plot-based forest censuses. We combined high-resolution airborne imaging spectroscopy and a ground-based tree canopy census to investigate whether tree canopies supporting lianas could be discriminated from tree canopies with no liana coverage. Using support vector machine algorithms, we achieved accuracies of nearly 90% in discriminating the presence–absence of lianas, and low error (15.7% RMSE) when predicting liana percent canopy cover. When applied to the full image of the study site, our model had a 4.1% false-positive error rate as validated against an independent plot-level dataset of liana canopy cover. Using the derived liana cover classification map, we show that 6.1%–10.2% of the 1823 ha study site has high-to-severe (50–100%) liana canopy cover. Given that levels of liana infestation are increasing in Neotropical forests and can result in high tree mortality, the extent of high-to-severe liana canopy cover across the landscape may have broad implications for ecosystem function and forest carbon storage. The ability to accurately map landscape-scale liana infestation is crucial to quantifying their effects on forest function and uncovering the mechanisms underlying their increase.

When the Single Matters more than the Group (II): Addressing the Problem of High False Positive Rates in Single Case Voxel Based Morphometry Using Non-parametric Statistics.

In recent years, an increasing number of studies have used Voxel Based Morphometry (VBM) to compare a single patient with a psychiatric or neurological condition of interest against a group of healthy controls. However, the validity of this approach critically relies on the assumption that the single patient is drawn from a hypothetical population with a normal distribution and variance equal to that of the control group. In a previous investigation, we demonstrated that family-wise false positive error rate (i.e., the proportion of statistical comparisons yielding at least one false positive) in single case VBM are much higher than expected (Scarpazza et al., 2013). Here, we examine whether the use of non-parametric statistics, which does not rely on the assumptions of normal distribution and equal variance, would enable the investigation of single subjects with good control of false positive risk. We empirically estimated false positive rates (FPRs) in single case non-parametric VBM, by performing 400 statistical comparisons between a single disease-free individual and a group of 100 disease-free controls. The impact of smoothing (4, 8, and 12 mm) and type of pre-processing (Modulated, Unmodulated) was also examined, as these factors have been found to influence FPRs in previous investigations using parametric statistics. The 400 statistical comparisons were repeated using two independent, freely available data sets in order to maximize the generalizability of the results. We found that the family-wise error rate was 5% for increases and 3.6% for decreases in one data set; and 5.6% for increases and 6.3% for decreases in the other data set (5% nominal). Further, these results were not dependent on the level of smoothing and modulation. Therefore, the present study provides empirical evidence that single case VBM studies with non-parametric statistics are not susceptible to high false positive rates. The critical implication of this finding is that VBM can be used to characterize neuroanatomical alterations in individual subjects as long as non-parametric statistics are employed.

Sequential sampling plan for assessing corn rootworm (Coleoptera: Chrysomelidae) larval injury to Bt maize

In-field product performance assessments are an essential component of corn rootworm (Diabrotica spp.; CRW) resistance management plans for transgenic maize (Zea mays L.) products expressing proteins derived from the bacterium Bacillus thuringiensis (Bt). The goal of a successful field sampling program is to accurately characterize in-field product performance while also minimizing resource demand, as collection of maize root samples to evaluate CRW injury can present resource challenges such as labor intensiveness, potential safety issues, and a limited time window available for sampling. A resource-efficient sequential sampling plan was developed that utilizes data-driven root injury threshold values derived from benchmark product performance data for both single and pyramided Bt maize traits for CRW control. This sequential sampling methodology incorporates unbiased sampling and controlled false positive and false negative error rates, enabling accurate assessment decisions to be made with efficient resource use. Our proposed approach enables systematic and effective classification of in-field Bt maize product performance, with applications to other CRW control technologies besides Bt maize products.