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Concept: Metrology

152

A paper-based, multiplexed, microfluidic assay has been developed to visually measure alanine aminotransferase (ALT) in a fingerstick sample, generating rapid, semi-quantitative results. Prior studies indicated a need for improved accuracy; the device was subsequently optimized using an FDA-approved automated platform (Abaxis Piccolo Xpress) as a comparator. Here, we evaluated the performance of the optimized paper test for measurement of ALT in fingerstick blood and serum, as compared to Abaxis and Roche/Hitachi platforms. To evaluate feasibility of remote results interpretation, we also compared reading cell phone camera images of completed tests to reading the device in real time.

Concepts: Measurement, Metrology, Alanine transaminase, Psychometrics, Test method, Java, Mobile phone, Camera phone

149

The study aimed to evaluate the test-retest reliability of a newly developed 356 Soccer Shooting Test (356-SST), and the discriminative ability of this test with respect to the soccer players' proficiency level and leg dominance. Sixty-six male soccer players, divided into three groups based on their proficiency level (amateur, n = 24; novice semi-professional, n = 18; and experienced semi-professional players, n = 24), performed 10 kicks following a two-step run up. Forty-eight of them repeated the test on a separate day. The following shooting variables were derived: ball velocity (BV; measured via radar gun), shooting accuracy (SA; average distance from the ball-entry point to the goal centre), and shooting quality (SQ; shooting accuracy divided by the time elapsed from hitting the ball to the point of entry). No systematic bias was evident in the selected shooting variables (SA: 1.98±0.65 vs. 2.00±0.63 m; BV: 24.6±2.3 vs. 24.5±1.9 m s-1; SQ: 2.92±1.0 vs. 2.93±1.0 m s-1; all p>0.05). The intra-class correlation coefficients were high (ICC = 0.70-0.88), and the coefficients of variation were low (CV = 5.3-5.4%). Finally, all three 356-SST variables identify, with adequate sensitivity, differences in soccer shooting ability with respect to the players' proficiency and leg dominance. The results suggest that the 356-SST is a reliable and sensitive test of specific shooting ability in men’s soccer. Future studies should test the validity of these findings in a fatigued state, as well as in other populations.

Concepts: Measurement, Metrology, Evaluation methods, Psychometrics, Reliability, Test-retest, Multiplication, The Players

42

Virulence is a microbial property that is realized only in susceptible hosts. There is no absolute measurement for virulence, and consequently it is always measured relative to a standard, usually another microbe or host. This article introduces the concept of pathogenic potential, which provides a new approach to measuring the capacity of microbes for virulence. The pathogenic potential is proportional to the fraction of individuals who become symptomatic after infection with a defined inoculum and can include such attributes as mortality, communicability, and the time from infection to disease. The calculation of the pathogenic potential has significant advantages over the use of the lethal dose that kills 50% of infected individuals (LD50) and allows direct comparisons between individual microbes. An analysis of the pathogenic potential of several microbes for mice reveals a continuum, which in turn supports the view that there is no dividing line between pathogenic and nonpathogenic microbes.

Concepts: Archaea, Infectious disease, Bacteria, Microbiology, Measurement, Metrology, Microorganism

31

To investigate whether the daily workload per nurse (Oulu Patient Classification (OPCq)/nurse) as measured by the RAFAELA system correlates with different types of patient safety incidents and with patient mortality, and to compare the results with regressions based on the standard patients/nurse measure.

Concepts: Measurement, Metrology, Test method

28

A simplified method for measuring the fluidic resistance (R(fluidic)) of microfluidic channels is presented, in which the electrical resistance (R(elec)) of a channel filled with a conductivity standard solution can be measured and directly correlated to R(fluidic) using a simple equation. Although a slight correction factor could be applied in this system to improve accuracy, results showed that a standard voltage meter could be used without calibration to determine R(fluidic) to within 12% error. Results accurate to within 2% were obtained when a geometric correction factor was applied using these particular channels. When compared to standard flow rate measurements, such as meniscus tracking in outlet tubing, this approach provided a more straightforward alternative and resulted in lower measurement error. The method was validated using 9 different fluidic resistance values (from ∼40 to 600kPasmm(-3)) and over 30 separately fabricated microfluidic devices. Furthermore, since the method is analogous to resistance measurements with a voltage meter in electrical circuits, dynamic R(fluidic) measurements were possible in more complex microfluidic designs. Microchannel R(elec) was shown to dynamically mimic pressure waveforms applied to a membrane in a variable microfluidic resistor. The variable resistor was then used to dynamically control aqueous-in-oil droplet sizes and spacing, providing a unique and convenient control system for droplet-generating devices. This conductivity-based method for fluidic resistance measurement is thus a useful tool for static or real-time characterization of microfluidic systems.

Concepts: Measurement, Metrology, Test method, Microfluidics, Measuring instrument, Electrical measurements, Electrical resistance, Ohmmeter

28

The performance of three different types of ion mobility spectrometer (IMS) devices: GDA2 with a radioactive ion source (Airsense, Germany), UV-IMS with a photo-ionization source (G.A.S. Germany) and VG-Test with a corona discharge source (3QBD, Israel) was studied. The gas-phase ion chemistry in the IMS devices affected the species formed and their measured reduced mobility values. The sensitivity and limit of detection for trimethylamine (TMA), putrescine and cadaverine were compared by continuous monitoring of a stream of air with a given concentration of the analyte and by measurement of headspace vapors of TMA in a sealed vial. Preprocessing of the mobility spectra and the effectiveness of multivariate curve resolution techniques (MCR-LASSO) improved the accuracy of the measurements by correcting baseline effects and adjusting for variations in drift time as well as enhancing the signal to noise ratio and deconvolution of the complex data matrix to their pure components. The limit of detection for measurement of the biogenic amines by the three IMS devices was between 0.1 and 1.2ppm (for TMA with the VG-Test and GDA, respectively) and between 0.2 and 0.7ppm for putrescine and cadaverine with all three devices. Considering the uncertainty in the LOD determination there is almost no statistically significant difference between the three devices although they differ in their operating temperature, ionization method, drift tube design and dopant chemistry. This finding may have general implications on the achievable performance of classic IMS devices.

Concepts: Mass spectrometry, Measurement, Metrology, Statistical significance, Analytical chemistry, Plasma, Biogenic amine, Ion mobility spectrometry

28

BACKGROUND: To assess the presence and extent of photophobia in children with intermittent exotropia (X[T]) using the contrast sensitivity test. METHODS: Fifty-eight children with X(T) and 34 normal controls were studied with the functional acuity contrast test. Each participant viewed the stimuli of contrast monocularly and binocularly under photopic and mesopic conditions, performed with and without glare. Photophobia was defined as a reduction of contrast sensitivity caused by glare light. We compared the photophobia of children with X(T) to that of normal controls, and to the photophobia 3 months after muscle surgery. RESULTS: With stimuli of glare, the contrast sensitivity of children with X(T) was suppressed at intermediate spatial frequencies under mesopic condition (p = 0.006 for 6 cycles per degree [cpd], p = 0.027 for 12 cpd), whereas that of normal controls showed no difference. It occurred when X(T) patients viewed targets binocularly, and significantly improved after strabismus surgery (p = 0.003 at 6 cpd). The measured photophobia of X(T) was strongly correlated to the photophobia symptoms reported by parents (p = 0.002). CONCLUSIONS: The mesopic contrast sensitivity with glare can represent the photophobia of children with X(T). Contrast sensitivity may be a useful measure for monitoring symptoms related to X(T).

Concepts: Measurement, Metrology, Psychometrics, Vision, Test method, Strabismus, Exotropia, Strabismus surgery

28

BACKGROUND: The Alzheimer’s Disease Assessment Scale-Cognitive Behavior section (ADAS-Cog) is the most widely used measure of cognitive performance in AD clinical trials. This key role has rightly brought its performance under increased scrutiny with recent research using traditional psychometric methods, questioning the ADAS-Cog’s ability to adequately measure early-stage disease. However, given the limitations of traditional psychometric approaches, herein we use the more sophisticated Rasch Measurement Theory (RMT) methods to fully examine the strengths and weaknesses of the ADAS-Cog, and identify potential paths toward its improvement. METHODS: We analyzed AD Neuroimaging Initiative (ADNI) ADAS-Cog data (675 measurements across four time-points over 2 years) from the AD participants. RMT analysis was undertaken to examine three broad areas: adequacy of scale-to-sample targeting; degree to which, taken together, the ADAS-Cog items adequately perform as a measuring instrument; and how well the scale measured the subjects in the current sample. RESULTS: The 11 ADAS-Cog components mapped-out a measurement continuum, worked together adequately, and were stable across different time-points and samples. However, the scale did not prove to be a good match to the patient sample supporting previous research. RMT analysis also identified problematic “gaps” and “bunching” of the components across the continuum. CONCLUSION: Although the ADAS-Cog has the building blocks of a good measurement instrument, this sophisticated analysis confirms limitations with potentially serious implications for clinical trials. Importantly, and unlike traditional psychometric methods, our RMT analysis has provided important clues aimed at solving the measurement problems of the ADAS-Cog.

Concepts: Measurement, Metrology, Psychometrics, Test method, Measuring instrument

28

The measurement of the Planck constant, h, is entering a new phase. The CODATA 2010 recommended value is 6.626 069 57 × 10(-34) J s, but it has been a long road, and the trip is not over yet. Since its discovery as a fundamental physical constant to explain various effects in quantum theory, h has become especially important in defining standards for electrical measurements and soon, for mass determination. Measuring h in the International System of Units (SI) started as experimental attempts merely to prove its existence. Many decades passed while newer experiments measured physical effects that were the influence of h combined with other physical constants: elementary charge, e, and the Avogadro constant, N(A). As experimental techniques improved, the precision of the value of h expanded. When the Josephson and quantum Hall theories led to new electronic devices, and a hundred year old experiment, the absolute ampere, was altered into a watt balance, h not only became vital in definitions for the volt and ohm units, but suddenly it could be measured directly and even more accurately. Finally, as measurement uncertainties now approach a few parts in 10(8) from the watt balance experiments and Avogadro determinations, its importance has been linked to a proposed redefinition of a kilogram unit of mass.The path to higher accuracy in measuring the value of h was not always an example of continuous progress. Since new measurements periodically led to changes in its accepted value and the corresponding SI units, it is helpful to see why there were bumps in the road and where the different branch lines of research joined in the effort. Recalling the bumps along this road will hopefully avoid their repetition in the upcoming SI redefinition debates. This paper begins with a brief history of the methods to measure a combination of fundamental constants, thus indirectly obtaining the Planck constant. The historical path is followed in the section describing how the improved techniques and discoveries in quantum mechanics steadily reduced the uncertainty of h. The central part of this review describes the technical details of the watt balance technique, which is a combination of the mechanical and electronic measurements that now determine h as a direct result, i.e. not requiring measured values of additional fundamental constants. The first technical section describes the basics and some of the common details of many watt balance designs. Next is a review of the ongoing advances at the (currently) seven national metrology institutions where these experiments are pursued. A final summary of the recent h determinations of the last two decades shows how history keeps repeating itself; there is again a question of whether there is a shift in the newest results, albeit at uncertainties that are many orders of magnitude less than the original experiments. The conclusion is that there is room for further development to resolve these differences and find new ideas for a watt balance system with a more universal application. Since the next generation of watt balance experiments are expected to become kilogram realization standards, the historical record suggests that there is yet a need for proof that Planck constant results are finally reproducible at an acceptable uncertainty.

Concepts: Measurement, Metrology, Units of measurement, Kilogram, Elementary charge, Planck constant, Physical constant, Planck units

28

Miranda J, Brunet Ll, Roset P, Farré M, Mendieta C. Reliability of two measurement indices for gingival enlargement. J Periodont Res 2012; 47: 776-782. © 2012 John Wiley & Sons A/S Background and Objective:  The objective of this study was to analyze the concordance of the vertical gingival overgrowth index (GOi) and the horizontal Miranda & Brunet index (MBi) and to compare their reliability and reproducibility for an early diagnosis of gingival enlargement. A wide range of methods has been employed to determine the severity of drug-induced gingival enlargement (DIGE) that has resulted in uncertainty with regard to the prevalence of this side effect. In recent studies, different indices have been used to grade DIGE. The large variability observed between studies and the differences between vertical and horizontal gingival-enlargement measurements could be the result of the use of nonreliable indices during the measurement process. Some indices involve invasive procedures that require many measurements, or even a data-processing system, while others are less convenient and technically expensive and complex. In previous studies we used two complementary indices - the vertical GOi and the horizontal MBi. The results of these studies found some differences between both indices, with the MBi rendering higher estimates of DIGE prevalence that was attributed to its greater sensitivity for the detection of minimal changes in gingival thickness. To our knowledge, there are no studies comparing different measurement indices for gingival enlargement that are supported by statistical concordance analysis. Material and Methods:  Twelve plaster casts from patients who had worn orthodontic brackets, and who had different degrees of chronic inflammatory gingival enlargement, were analyzed. Three previously trained examiners registered twice the degree of buccal overgrowth, using the GOi and MBi, in all cast models with a minimum interval of 7 d between the first and the second evaluation. In total, from each cast, measurements from 16 gingival sites were taken using the GOi, and from nine gingival units (mesial and distal sites measurements) using the MBi. Concordance analysis of the registered measurements (intra-examiner and among examiners) for each index and between indices was assessed using the nonweighted Kappa index with a confidence interval of 95%. Results:  We obtained 648 values for the GOi and the MBi. The overall score 0 (indicating absence of enlargement) was 32.7% and 19.8% for GOi and MBi, respectively, score 1 (light/moderate) was 39.7% and 48.1%, and score 2 (severe) was 27.6% and 32.1%. Concordance analysis for each index showed intra-examiner Kappa values of 0.820 for the GOi and 0.830 for the MBi. Interexaminer Kappa values were 0.720 for the GOi and 0.770 for the MBi. Concordance between indices showed Kappa values for the same examiner of 0.600, whereas concordance among different examiners was 0.550. Discrepancies between indices indicated a systematic skew, with 79-82.1% of discrepancy associated with a higher value for the MBi compared with the GOi. Conclusion:  Both gingival enlargement indices analyzed are reliable, complementary and applicable for measuring gingival overgrowth. However, the MBi shows, with fewer measurements, a greater sensitivity than the GOi for the detection of the early stages of gingival enlargement, being adequate for the screening of large populations at risk.

Concepts: Measurement, Metrology, Psychometrics, Units of measurement, Systems of measurement, Index, Gingival enlargement, Phenytoin