Towards a single-point method for measuring phosphate sorption by soils

Soil Research ◽  
2000 ◽  
Vol 38 (6) ◽  
pp. 1099 ◽  
Author(s):  
N. J. Barrow
Keyword(s):  
Single Point ◽  
Solution Concentration ◽  
Point Method ◽  
High Rate ◽  
Point Estimate ◽  
Single Pair ◽  
Single Application ◽  
Phosphate Sorption ◽  
Point Estimates ◽  
Sorption Curve

Data from 4 separate studies using widely differing soils were used to assesswhether single-point estimates of the relative buffering could be used asestimates of buffering derived from fitted curves. The relative bufferingcapacity of soils for P was summarized using the ‘O&Svalue’. This is the increase in P sorption between concentrations of 0.25 and 0.35 mg P/L.Phosphate sorption curves were described by the modified Freundlich equation:S = acb – q, whereS ( g/g) is the measured sorption,c ( g/mL) the solution concentration, anda, b, and qare parameters. The fitted O&S value is given by:a (0.35 b – 0.25b ). If a single pair of values for sorption andconcentration is measured, rather than a sorption curve, thea value can be estimated from (S+ q)/cb . An estimate of the O&S value can beobtained from (S + q) (0.35b – 0.25 b)/c b .Because the b parameter occurs in both the numerator andthe denominator, the single-point estimate of the O&S value was notvery sensitive to the value allocated to b provided thevalue of c was in the range 2–5 mg P/L. Formost of the soils of low to moderate buffering, the P extracted by the Colwellreagent was a useful estimate of q. For these soils, thesingle-point estimates using this value of q weresimilar to the values found from the fitted curves. One group of exceptionswere some soils of low buffering which had received a single application ofphosphate at a high rate. For these soils, the Colwell reagent extracted largeamounts of phosphate. Another group of exceptions were soils of highbuffering. For these the Colwell reagent gave values much lower than thefitted value of q and was of little value in improvingthe calculation of single-point estimates. The single point estimates forthese soils were about 20% too low but nevertheless well correlatedwith the values from the fitted curves.

scholarly journals Is it Possible to Find a Good Point Estimate of a Calibrated Radiocarbon Date?

Radiocarbon ◽  
2007 ◽  
Vol 49 (2) ◽  
pp. 393-401 ◽  
Author(s):  
Adam Michczyński
Keyword(s):  
Computer Simulation ◽  
Confidence Intervals ◽  
Single Point ◽  
Radiocarbon Date ◽  
Point Estimate ◽  
Local Mode ◽  
True Value ◽  
Point Estimates ◽  
Good Point ◽  
Accepted Practice

The result from probabilistic calibration of a radiocarbon date is given in the form of a probability density function. Consequently, reporting a 68% or 95% confidence interval has became a commonly accepted practice. However, many users of 14C dates still try to present the results of calibration as a single point. This manner of presentation is often applied during the construction of age-depth models due to its convenience and simplicity. In this paper, the author tests whether it is possible to find a good point estimate of a calibrated 14C date. The idea of the tests is to compare, using computer simulation, the true value of the calendar age with the age calculated based on the probabilistic calibration of the 14C date and the method of finding the point estimate. The test is carried out for the following point estimates: mode, median, average, the central point of the confidence intervals, and the local mode inside the confidence intervals. The results show that none of these may be considered as a good estimate.

Comparing simple methods for measuring phosphate sorption by soils

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1433 ◽  
Author(s):  
D. G. Allen ◽  
N. J. Barrow ◽  
M. D. A. Bolland
Keyword(s):  
Single Point ◽  
Phosphate Sorption ◽  
Indirect Measures ◽  
Oxalate Solution ◽  
Western Australian ◽  
Sorption Curve

Phosphate sorption curves were measured for 103 Western Australian soils sampled from farmers’ fields. A measure of phosphate buffering obtained from a fitted curve was compared with indexes obtained from single-point measurements of phosphate sorption. The single-point indexes were adjusted for the phosphate present in the sampled soils by adding the phosphate extracted by the bicarbonate reagent to the measured sorption. Iron and aluminium extracted by an oxalate solution were measured as indirect indexes. The single-point indexes were closely correlated with the values obtained from the sorption curve. Their correlation was much larger than that of indirect measures.

A new approach to facilitate diagnosis of nonalcoholic fatty liver disease through a galactose single point method in rats with fatty liver

2013 ◽  
Vol 45 (2) ◽  
pp. 134-141 ◽  
Author(s):  
Jr-Ting Lee ◽  
Li-Heng Pao ◽  
Meei-Shyuan Lee ◽  
Jiunn-Wang Liao ◽  
Chi-Min Shih ◽  
...  
Keyword(s):  
Liver Disease ◽  
Fatty Liver ◽  
Nonalcoholic Fatty Liver Disease ◽  
Fatty Liver Disease ◽  
Single Point ◽  
Point Method ◽  
New Approach ◽  
Nonalcoholic Fatty Liver

scholarly journals Bayesian estimation of the seroprevalence of antibodies to SARS-CoV-2

JAMIA Open ◽  
2020 ◽  
Author(s):  
Qunfeng Dong ◽  
Xiang Gao
Keyword(s):  
Probability Distribution ◽  
Large Scale ◽  
Prior Probability ◽  
Probability Distributions ◽  
Single Point ◽  
Point Estimates ◽  
Specificity And Sensitivity ◽  
Large Scale Dataset ◽  
The Us ◽  
Antibody Tests

Abstract Accurate estimations of the seroprevalence of antibodies to severe acute respiratory syndrome coronavirus 2 need to properly consider the specificity and sensitivity of the antibody tests. In addition, prior knowledge of the extent of viral infection in a population may also be important for adjusting the estimation of seroprevalence. For this purpose, we have developed a Bayesian approach that can incorporate the variabilities of specificity and sensitivity of the antibody tests, as well as the prior probability distribution of seroprevalence. We have demonstrated the utility of our approach by applying it to a recently published large-scale dataset from the US CDC, with our results providing entire probability distributions of seroprevalence instead of single-point estimates. Our Bayesian code is freely available at https://github.com/qunfengdong/AntibodyTest.

scholarly journals A Note on the Asymptotic Behavior of the Heights in $b$-Tries for $b$ Large

10.37236/1517 ◽  
2000 ◽  
Vol 7 (1) ◽  
Author(s):  
Charles Knessl ◽  
Wojciech Szpankowski
Keyword(s):  
Asymptotic Behavior ◽  
Saddle Point ◽  
Generating Functions ◽  
Single Point ◽  
Extreme Value ◽  
Limiting Distribution ◽  
Point Method ◽  
Saddle Point Method ◽  
Numerical Verification ◽  
Height Distribution

We study the limiting distribution of the height in a generalized trie in which external nodes are capable to store up to $b$ items (the so called $b$-tries). We assume that such a tree is built from $n$ random strings (items) generated by an unbiased memoryless source. In this paper, we discuss the case when $b$ and $n$ are both large. We shall identify five regions of the height distribution that should be compared to three regions obtained for fixed $b$. We prove that for most $n$, the limiting distribution is concentrated at the single point $k_1=\lfloor \log_2 (n/b)\rfloor +1$ as $n,b\to \infty$. We observe that this is quite different than the height distribution for fixed $b$, in which case the limiting distribution is of an extreme value type concentrated around $(1+1/b)\log_2 n$. We derive our results by analytic methods, namely generating functions and the saddle point method. We also present some numerical verification of our results.

scholarly journals Two-Stage Single-Arm Trials Are Rarely Analyzed Effectively or Reported Adequately

2021 ◽  
pp. 1813-1820
Author(s):  
Michael J. Grayling ◽  
Adrian P. Mander
Keyword(s):  
Final Stage ◽  
Interim Analysis ◽  
Primary Outcome ◽  
Point Estimate ◽  
Two Stage ◽  
Stage Design ◽  
Patient Subgroup ◽  
Future Studies ◽  
Point Estimates ◽  
Outcome Trial

PURPOSE Two-stage single-arm designs have historically been the most common design used in phase II oncology. They remain a mainstay today, particularly for trials in rare subgroups. Consequently, it is imperative such studies be designed, analyzed, and reported effectively. We comprehensively review such trials to examine whether this is the case. METHODS Oncology trials that used Simon's two-stage design over a 5-year period were identified and reviewed. They were evaluated for whether they reported sufficient design (eg, required sample size) and analysis (eg, CI) details. Articles that did not adjust their inference for the incorporation of an interim analysis were also reanalyzed. RESULTS Four-hundred twenty-five articles were included. Of these, just 47.5% provided the five components that ensure design reproducibility. Only 1.2% and 2.1% reported an adjusted point estimate or CI, respectively. Just 55.3% provided the final stage rejection bound, indicating many trials did not test a hypothesis for their primary outcome. Trial reanalyses suggested reported point estimates underestimated treatment effects and reported CIs were too narrow. CONCLUSION Key design details of two-stage single-arm trials are often unreported. Their inference is rarely performed such as to remove bias introduced by the interim analysis. These findings are particular alarming when considered against the growing trend in which nonrandomized trials make up a large proportion of all evidence on a treatment's effectiveness in a rare biomarker-defined patient subgroup. Future studies must improve the way they are analyzed and reported.

scholarly journals Lack of Effect of Simultaneously Administered Didanosine Encapsulated Enteric Bead Formulation (Videx EC) on Oral Absorption of Indinavir, Ketoconazole, or Ciprofloxacin

2002 ◽  
Vol 46 (2) ◽  
pp. 385-391 ◽  
Author(s):  
Bharat D. Damle ◽  
Vanaja Mummaneni ◽  
Sanjeev Kaul ◽  
Catherine Knupp
Keyword(s):  
Oral Absorption ◽  
Historical Data ◽  
Point Estimate ◽  
Open Label ◽  
Time Curve ◽  
Geometric Means ◽  
Point Estimates ◽  
Concentration Time ◽  
Crossover Studies ◽  
Post Hoc

ABSTRACT Didanosine formulation that contains a buffer to prevent it from acid-mediated degradation can result in a significant decrease in the oral absorption of certain drugs because of interactions with antacids. An enteric formulation of didanosine is unlikely to cause such drug interactions because it lacks antacids. This study was undertaken to determine whether the enteric bead formulation of didanosine (Videx EC) influences the bioavailability of indinavir, ketoconazole, and ciprofloxacin, three drugs that are representative of a broader class of drugs affected by interaction with antacids. Healthy subjects of either gender were enrolled in three separate open-label, single-dose, two-way crossover studies. Subjects were randomized to treatment A (800 mg of indinavir, 200 mg of ketoconazole, or 750 mg of ciprofloxacin) or treatment B (same dose of indinavir, ketoconazole, or ciprofloxacin, but with 400 mg of didanosine as an encapsulated enteric bead formulation). A lack of interaction was concluded if the 90% confidence interval (CI) of the ratio of the geometric means of log-transformed C max and AUC0-∞ values (i.e., values for the area under the concentration-time curve from time zero to infinity) of indinavir, ketoconazole, and ciprofloxacin were contained entirely between 0.75 and 1.33. For indinavir (n = 23), the point estimate (90% CI; minimum, maximum) of the ratios of C max and AUC0-∞ values were 0.99 (0.91, 1.06) and 0.96 (0.91, 1.02), respectively. In the ketoconazole study, 3 of 24 subjects showed anomalous absorption of ketoconazole (i.e., an ∼8-fold-lower AUC compared to historical data), which was the reference treatment. A post hoc analysis performed after these three subjects were excluded indicated that the point estimates (90% CI) of the ratios of Cmax and AUC0-∞ values were 0.99 (0.86, 1.14) and 0.97 (0.85, 1.10), respectively. For ciprofloxacin (n = 16), the point estimate (90% CI) of the ratios of C max and AUC0-∞ values were 0.92 (0.79, 1.07) and 0.91 (0.76, 1.08), respectively. All three studies clearly indicated a lack of interaction. The T max and t 1/2 for indinavir, ketoconazole, and ciprofloxacin were similar between treatments. Our results showed that the lack of interaction of didanosine encapsulated enteric bead formulation with indinavir, ketoconazole, and ciprofloxacin indicates that this enteric formulation of didanosine can be concomitantly administered with drugs whose bioavailability is known to be reduced by interaction with antacids.

STIMULATION OF GROWTH PROCESSES IN EGGPLANT PLANTS GROWN IN THE KHABAROVSK REGION

2020 ◽  
Vol 15 (5) ◽  
pp. 658-668
Author(s):  
T.M. Trifonova ◽  
◽  
T.K. Stupko ◽  
Keyword(s):  
Leaf Blade ◽  
Solution Concentration ◽  
High Rate ◽  
Morphological Parameters ◽  
Growth Processes ◽  
Rate Of Growth ◽  
Inhibition Of Growth ◽  
Open Ground ◽  
Working Solution ◽  
Sowing Seed

The article presents the results of studies for 2019. The aim of the study was to identify the effectiveness of growth regulators Prorotok and HB-101 in stimulating growth processes in seeds and seedlings of eggplant culture grown in the Khabarovsk Territory. The objectives of the study were to study the growth-stimulating effect of the studied drugs based on the analysis of data on the energy of germination and germination of seeds, as well as morphological parameters of seedlings of the eggplant culture grown in the territory of the village. Dzhonka of the Nanay district of the Khabarovsk Territory. The research was carried out on two varieties of eggplant Boyarin F1 and Mishutka. The experiment was carried out in three replicates in accordance with the agricultural technology generally accepted for the territory of the Khabarovsk Territory. As a result of the studies carried out, inhibition of growth processes was revealed in the variants of the experiment with pre-sowing seed treatment with Prorostk and HB-101 in the form of soaking them for two hours in working solutions of preparations with a concentration of 0.25, 0.5, 1% compared to the control a variant in which the seeds were soaked in water. Analysis of the morphological parameters of eggplant seedlings revealed the following. In the variants of the experiment with the concentration of the Prorostka working solution of 0.25%, the plants of varieties Mishutka and Boyarin F1 showed an increase in the length of the leaf blade by 8 and 13%, the length of the stem by 7 and 17%, respectively, compared with the control. In the variants of the experiment, in which the plants were treated with the Germination solution with a concentration of 0.5%, a significant increase in the length of the leaf blade by 6 and 11%, and the length of the stem by 8 and 15%, respectively, was revealed. The analysis of the efficiency of HB-101 showed a growth-stimulating effect at the stage from seed germination to the formation of the first two true leaves in plants of the Mishutka variety in the variant with a working solution concentration of 0.25%. The increase in the length of the leaf in this case was up to 35%, the length of the stem up to 20% in comparison with the control variant. In the period from two true leaves to planting seedlings in open ground, a high rate of growth processes was noted in variants with working solutions HB-101 0.25 and 0.5%. The use of the HB-101 preparation at the stage of presowing treatment, as well as during the cultivation of seedlings of plants of the Boyarin F1 variety, is not advisable, since a decrease in the rate of growth processes was revealed in the plantings of this variety in comparison with the control option.

The Utility of a Single-Point Dosing Protocol for Predicting Steady-State Lithium Levels

1986 ◽  
Vol 148 (4) ◽  
pp. 401-405 ◽  
Author(s):  
Paul J. Perry ◽  
Bruce Alexander ◽  
Randall A. Prince ◽  
Frederick J. Dunner
Keyword(s):  
Steady State ◽  
Affective Disorder ◽  
Single Point ◽  
Test Dose ◽  
Point Method ◽  
Lithium Level ◽  
Clinical Interpretation ◽  
Serum Lithium Level ◽  
Steady State Serum

Two methods for predicting steady-state serum lithium level were compared prospectively in in-patients suffering from affective disorder. A single-point prospective administration model that required a single 24-hour serum lithium level, following a test dose produced statistically similar predictions of the observed steady-state lithium levels as did a model that required 12- and 36-hour levels. However, the latter two-point method produced significantly more accurate predictions from clinical interpretation. Although the two-point approach is preferable, the single-point method is clinically acceptable if its limitations of accuracy are taken into consideration.

scholarly journals Do non-inferiority trials of reduced intensity therapies show reduced effects? A descriptive analysis

BMJ Open ◽  
2018 ◽  
Vol 8 (3) ◽  
pp. e019494 ◽  
Author(s):  
Scott K Aberegg ◽  
Andrew M Hersh ◽  
Matthew H Samore
Keyword(s):  
Active Control ◽  
Absolute Risk ◽  
Descriptive Analysis ◽  
High Rate ◽  
Experimental Therapy ◽  
Favourable Result ◽  
Point Estimates ◽  
Full Intensity ◽  
Reduced Intensity

ObjectivesTo identify non-inferiority trials within a cohort where the experimental therapy is the same as the active control comparator but at a reduced intensity and determine if these non-inferiority trials of reduced intensity therapies have less favourable results than other non-inferiority trials in the cohort. Such a finding would provide suggestive evidence of biocreep in these trials.DesignThis metaresearch study used a cohort of non-inferiority trials published in the five highest impact general medical journals during a 5-year period. Data relating to the characteristics and results of the trials were abstracted.Primary outcome measuresProportions of trials with a declaration of superiority, non-inferiority and point estimates favouring the experimental therapy and mean absolute risk differences for trials with outcomes expressed as a proportion.ResultsOur search yielded 163 trials reporting 182 non-inferiority comparisons; 36 comparisons from 31 trials were between the same therapy at reduced and full intensity. Compared with trials not evaluating reduced intensity therapies, fewer comparisons of reduced intensity therapies demonstrated a favourable result (non-inferiority or superiority) (58.3%vs82.2%; P=0.002) and fewer demonstrated superiority (2.8%vs18.5%; P=0.019). Likewise, point estimates for reduced intensity therapies more often favoured active control than those for other trials (77.8%vs39.7%; P<0.001) as did mean absolute risk differences (+2.5% vs −0.7%; P=0.018).ConclusionsNon-inferiority trials comparing a therapy at reduced intensity to the same therapy at full intensity showed reduced effects compared with other non-inferiority trials. This suggests these trials may have a high rate of type 1 errors and biocreep, with significant implications for the design and interpretation of future non-inferiority trials.

Sign in / Sign up

Export Citation Format

Share Document