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Results for “instrumental variable assumptions”

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PubMed1990

A new method for noninvasive quantitation of segmental myocardial wall thickening using technetium-99m 2-methoxy-isobutyl-isonitrile scintigraphy--results in normal subjects.

A quantitative index of regional myocardial wall motion obtained from electrocardiogram-gated perfusion images has been assessed. The assumption for the proposed algorithm is that, according to the partial volume effect, the recovery counts by the instrumentation is a function of the object size. Systo-diastolic changes in the detected radioactivity would therefore reflect changes in myocardial wall thickness. Ten normal volunteers were studied in control condition by 99mTc 2-methoxy-isobutyl-isonitrile scintigraphy. Electrocardiogram (ECG)-gated images were acquired in multiple projections. End-diastolic and end-systolic activity was measured along radii from the center to the edge of the left ventricle. Data are displayed as circumferential profiles and the percent systolic thickening determined according to the formula (end-systolic profile--end-diastolic profile) (end-diastolic profile + background) x 100.) The intra- and interobserver variabilities were +/- 5.4% and +/- 4.1%, respectively. Analysis of regional systolic thickening showed a heterogeneous pattern, with a maximal and minimum value of 35% and 27% located to the infero-apical and to the proximal anterior wall, respectively. Our values correlate well with those reported for normals using cine computed tomography or nuclear magnetic resonance.

Adult↗

PubMed2002

Theoretical assumptions and psychometric characteristics of the sense of personal control at work questionnaire.

UNLABELLED: Personal control is a very important determinant of stress experienced at work. This variable is taken into account in different models of stress, and its role in the relationship between stress and stress effects has been studied in many research projects. But there is still lack of in-depth theoretical considerations on various definitions of control, which would allow to develop precise operationalization of this phenomenon. The following issues are discussed in this paper: 1) theoretical assumptions important for proper construction of the Sense of Personal Control at Work (SPCW); 2) the origins of SPCW Questionnaire; 3) the results of empirical study on psychometric characteristics of the SPCW Questionnaire. A group of 160 subjects participated in the study; the SPCW Questionnaire was administered twice with a 2-week interval; at the first stage, it was used together with other instruments, such as Maslach Burnout Inventory, Stress at Work Questionnaire, Work Satisfaction Scale, general Health Questionnaire-28. Reliability coefficients: Cronbach alpha = 0.81; r(tt) = 0.69. VALIDITY: correlation coefficients between personal control and work satisfaction r = 0.44; stress at work r = -0.33; emotional exhaustion r = -0.28; personal accomplishment r = 0.25; depersonalisation r = 4.26; mental health r = -0.19. Exploratory factors analysis have not confirmed theoretical structure of the SPCW Questionnaire.

Adult↗

PubMed1992

The clinical Swiss army knife. Empirical evidence on the validity of IADL functional status measures.

To encourage the clinical use of functional status measures, tools have been developed that are shorter and easier to administer. This study was conducted to provide empirical evidence concerning the validity of instrumental activities of daily living (IADL) scales. Similar to previous findings, this study found that a 50-item questionnaire was suitable for patient self-completion. This scale also showed good reproducibility over a 2-week period, a unidimensional factor structure, internal consistency, predictable correlations with other health status measures, and the ability to distinguish formal service users from nonusers. On the other hand, the findings also clearly demonstrate that caution is warranted when choosing rating formats and scoring procedures, and when interpreting patient responses. Ratings of difficulty, nonperformance, and assistance received should not be assumed to be interchangeable nor to reflect underlying physical ability. A great deal of sample variability was found when the process validity, or the subjective meanings of these ratings was examined. Scalogram analysis also indicated that the assumption of hierarchical ordering is not justified. Based on these findings, minimal questioning, dichotomous responses categories, and aggregate scores are not recommended for discharge planning or monitoring individual patients.

Activities of Daily Living↗

PubMed2001

The Multiple Sclerosis Impact Scale (MSIS-29): a new patient-based outcome measure.

Changes in health policy have underlined the importance of evidence-based clinical practice and rigorous evaluation of patient-based outcomes. As patient-based outcome measurement is particularly important in treatment trials of multiple sclerosis, a number of disease-specific instruments have been developed recently. One limitation of these instruments is that none was developed using the standard psychometric approach of reducing a large item pool generated from people with multiple sclerosis. Consequently, an outcome measure for clinical trials of multiple sclerosis that is disease specific and combines patient perspective with rigorous psychometric methods will complement existing instruments. The aim of this study was to develop such a measure. Standard psychometric methods were used. A pool of 129 questionnaire items was generated from interviews with 30 people with multiple sclerosis, expert opinion and literature review. The questionnaire was administered by postal survey to 1530 people selected randomly from the Multiple Sclerosis Society membership database. Redundant items and those with limited measurement properties were removed. The remaining items (n = 41) were grouped into scales using factor analysis, and then refined to form the Multiple Sclerosis Impact Scale (MSIS-29), an instrument measuring the physical (20 items) and psychological (nine items) impact of multiple sclerosis. Five psychometric properties of the MSIS-29 (data quality, scaling assumptions, acceptability, reliability and validity) were examined in a separate postal survey of 1250 Multiple Sclerosis Society members. A preliminary responsiveness study of the MSIS-29 was undertaken in 55 people admitted for rehabilitation and intravenous steroid treatment of relapses. The MSIS-29 satisfied all psychometric criteria. Data quality was excellent, missing data were low (maximum 3.9%), item test-re-test reliability was high (r = 0.65-0.90) and scale scores could be generated for >98% of respondents. Item descriptive statistics, item convergent and discriminant validity, and factor analysis indicated that it was legitimate to generate scores for MSIS-29 scales by summing items. MSIS-29 scales showed good variability, small floor and ceiling effects, high internal consistency (Cronbach's alpha <or=0.91) and high test-re-test reliability (intraclass correlation <or=0.87). Correlations with other measures and the analysis of group differences provided evidence that the MSIS-29 measures the physical and psychological impact of multiple sclerosis. Effect sizes (physical scale = 0.82, psychological scale = 0.66) demonstrated preliminary evidence of good responsiveness. These results indicate the MSIS-29 is a clinically useful and scientifically sound patient-based outcome measure of the impact of multiple sclerosis suitable for clinical trials and epidemiological studies.

Evidence-Based Medicine↗

PubMed2006

Broadening perspectives on clinical performance assessment: rethinking the nature of in-training assessment.

CONTEXT: In-training assessment (ITA), defined as multiple assessments of performance in the setting of day-to-day practice, is an invaluable tool in assessment programmes which aim to assess professional competence in a comprehensive and valid way. Research on clinical performance ratings, however, consistently shows weaknesses concerning accuracy, reliability and validity. Attempts to improve the psychometric characteristics of ITA focusing on standardisation and objectivity of measurement thus far result in limited improvement of ITA-practices. PURPOSE: The aim of the paper is to demonstrate that the psychometric framework may limit more meaningful educational approaches to performance assessment, because it does not take into account key issues in the mechanics of the assessment process. Based on insights from other disciplines, we propose an approach to ITA that takes a constructivist, social-psychological perspective and integrates elements of theories of cognition, motivation and decision making. A central assumption in the proposed framework is that performance assessment is a judgment and decision making process, in which rating outcomes are influenced by interactions between individuals and the social context in which assessment occurs. DISCUSSION: The issues raised in the article and the proposed assessment framework bring forward a number of implications for current performance assessment practice. It is argued that focusing on the context of performance assessment may be more effective in improving ITA practices than focusing strictly on raters and rating instruments. Furthermore, the constructivist approach towards assessment has important implications for assessment procedures as well as the evaluation of assessment quality. Finally, it is argued that further research into performance assessment should contribute towards a better understanding of the factors that influence rating outcomes, such as rater motivation, assessment procedures and other contextual variables.

Clinical Competence↗

PubMed2005

Temperament in the clinical differentiation of depressed bipolar and unipolar major depressive patients.

OBJECTIVE: To examine differences in temperament profiles between patients with recurrent unipolar and bipolar depression. METHOD: Depressed individuals with recurrent major depressive disorder (MDD) (n = 94) and those with bipolar (n = 59) disorders (about equally divided between types I and II) were recruited by newspaper advertisement, radio and television announcements, flyers and newsletters, and word of mouth. All patients were interviewed using the Structured Clinical Interview for DSM III-R (SCID) and had the severity of their depressive episode assessed by means of the 17-item Hamilton Rating Scale for Depression. All patients filled out the TEMPS-A, a validated instrument. RESULTS: Temperament differences between bipolar and MDD patients were examined using MANCOVA. Overall significant effect of the fixed factor (bipolar vs. unipolar) was noted for the temperament scores [Hotelling's F((5,142)) = 2.47, p < 0.05]. Overall effects were found for age [F((5,142)) = 2.40, p < 0.05], but not for gender and severity of depression [F((5,142)) = 1.65, p = 0.15 and F((5,142)) = 0.66, p = 0.66, respectively]. Dependent variables included the five subscales of the TEMPS-A, but only the cyclothymic temperament scores showed significant between-group differences. LIMITATION: Small bipolar subsample cell sizes did not permit to test the specificity of the findings for bipolar II vs. bipolar I patients. CONCLUSION: The finding that the clyclothymic subscale is significantly elevated in the bipolar vs. the unipolar depressive group supports the theoretical assumptions upon which the scale is based, and suggests that it might become a useful tool for clinical and research purposes.

Adult↗

PubMed2005

Improving subjective scaling of pain using Rasch analysis.

UNLABELLED: Pain management outcomes assessment depends on valid measurement of pain. However, the validity of single-item scales, such as numeric or faces scales, with the assignment of ordinal numerical values to response scale categories, is questionable. The universal assumption that equal distances between response choices represent equal distances on the dimension being measured is essentially erroneous. Herein we demonstrate that Rasch analysis can be used to expose and repair scale inequity and reengineer scale structure. Thirty-one subjects with severe ocular surface disease repeatedly completed a 7-category faces pain scale. Rasch analysis demonstrated that response category 5 was underutilized, leading to disordering of the response scale. Collapsing category 5 into either category 4 or 6 produced an ordered 6-category faces scale that could be recalibrated with average Rasch person measures to create linear measurement on a continuous latent variable. The value of further alterations to the scale was explored, and the implication for scale redesign discussed. Rasch analysis could be applied to any subjective pain measure post-hoc to create linear measurement or applied during instrument development to optimize design. PERSPECTIVE: Single-item scales like the faces scale or a 1-10 numerical rating scale are commonly used for the subjective assessment of pain. However, scores applied to response categories are arbitrary, so do not represent equidistant steps in the underlying latent variable (pain). Scale inequities are easily demonstrable and repairable with Rasch analysis.

Adult↗

PubMed2026

Aerobic Fitness and Health-Related Phenotypes: A Two-Stage Phenome-Wide Mendelian Randomization Study.

PURPOSE: We investigated potentially causal associations between genetically predicted aerobic fitness and multiple health phenotypes using a two-stage phenome-wide Mendelian randomization (MR) study. METHODS: Genetically determined aerobic fitness, as operationalized by Cai et al., served as the exposure instrument. We screened 712 health-related phenotypes as outcomes using publicly available European-ancestry genome-wide association studies (GWAS) summary statistics from OpenGWAS (Discovery GWAS n > 5000), prioritizing non-UK Biobank/non-FinnGen datasets for Discovery when available and selecting an independent GWAS for validation. Associations were estimated using the MR-Robust Adjusted Profile Score method, controlled for multiple testing (5% false discovery rate) and unaffected by violations of MR assumptions (directional concordance between discovery and validation; no evidence of horizontal pleiotropy across inverse-variance weighted, MR-Egger, weighted-median, and weighted-mode methods; negative control analysis on hair color). RESULTS: We identified 108 discovery associations, of which 34 remained valid and statistically significant after validation. Higher genetically determined aerobic fitness was associated with lower lacunar stroke risk, lower arterial stiffness, higher heart rate variability, lower diastolic blood pressure, more favorable anthropometric measures, lower use of antidiabetic drugs, lower asthma risk, lower C-reactive protein, higher bone mineral density, favorable liver function biomarkers, favorable platelet-related traits, multiple blood count-derived hematological cell indices and counts, as well as higher years of schooling. Adverse associations were confined to atrial fibrillation, valvular heart disease, and systolic blood pressure. CONCLUSIONS: Genetically determined aerobic fitness is linked to a broad pattern of favorable cardiometabolic, inflammatory, musculoskeletal, respiratory, hepatic, and hematological phenotypes, alongside a narrow set of potential cardiovascular hazards.

Humans↗

PubMed1992

[Common attitudes about the effect of positive and negative mood on task related motivation].

Several theories on emotion and mood have stressed the close relationship between emotion and motivation. However, assumptions on mood contingent motivations have mainly been studied in the field of social behavior, and there are only few studies concerned with mood contingent task motivations, an area in which nit is possible to distinguish between two motivational sets, the deliberative and the implemented mind set. Assuming that positive mood is associated with a stronger task-oriented deliberative mind set, and that negative mood is associated with a stronger self-oriented deliberative mind set, and that implemented mind set should be intrinsically task-oriented during positive mood and instrumentally task-oriented during negative mood. The present paper is concerned with these assumptions from a subjective perspective: The respondents were asked about their lay perceptions of mood influences (positive, elated versus negative, sad mood) on task related motivations. In study I the respondents (N = 40) were asked about their deliberative mind sets during positive versus negative mood and about their general perceptions of mood influences on performance. In study II the respondents (N = 58) were requested to imagine situations which elicit positive, negative or neutral mood, and then to answer questions on deliberative and implemented mind sets during these states; they also hat to answer a general question about mood influences on task performance. Both quantitative and qualitative measures are used in these studies. The findings support the above general notions, and they additionally show that in the respondents' opinions negative mood effects are more variable than positive mood effects; further, that there are quite a few individual differences in assumed mood effects on task-related motivation.

Achievement↗

PubMed1998

Measurement of facial soft tissue mobility in man.

OBJECTIVE: The assessment of facial mobility is a key element in the treatment of patients with facial motor deficits. In this study, we explored the utility of a three-dimensional tracking system in the measurement of facial movements. METHODS AND RESULTS: First, the three-dimensional movement of potentially stable facial soft-tissue, headcap, and dental landmarks was measured with respect to a fixed space frame. Based on the assumption that the dental landmarks are stable, their motion during a series of standardized facial animations was subtracted from that of the facial and headcap landmarks to estimate their movement within the face. This residual movement was used to determine which points are relatively stable (< or = 1.5 mm of movement) and which are not (> or = 1.5 mm of movement). Headcap landmarks were found to be suitable as references during smile, cheek puff, and lip purse animations, and during talking. In contrast, skin-based landmarks were unsuitable as references because of their considerable and highly variable movement during facial animation. Second, the facial movements of patients with obvious facial deformities were compared with those of matched controls to characterize the face validity of three-dimensional tracking. In all instances, pictures that appear to be characteristic of the various functional deficits emerged. CONCLUSIONS: Our results argue that tracking instrumentation is a potentially useful tool in the measurement of facial mobility.

Adolescent↗

PubMed1998

Reproducibility of within-subject breath alcohol analysis.

Random samples from normal distributions are an important assumption for many statistical methods. The present study evaluates this assumption with regard to quantitative breath alcohol analyses. Eight individuals (six male and two female) consumed alcoholic beverages and subsequently provided replicate (n ranging from 22 to 69) breath samples to an infrared breath alcohol instrument within short time intervals. The serially collected data were treated with several descriptive and inferential methods. Descriptive results among the eight individuals included: mean 0.0420-0.1175 g/210 L, SD 0.0008-0.0045 g/210 L and CV: 1.9%-4.7%. Statistical tests for normality showed seven of the distributions to be reasonably normal (p > or = 0.25) and the other marginal (p = 0.051). A test for runs about the median showed random results (p > or = 0.10) for four individuals and non-random (p < or = 0.01) for the other four. The results suggest an individual's breath alcohol measurement, when appropriately collected and analysed, should be considered a random sample from a normal within-subject distribution. The existing variability in breath alcohol analysis, due largely to biological and sampling considerations, is acceptably minimized to warrant forensic application.

Adult↗

PubMed2005

[Classification of pharmaceutical services from the viewpoint of patient satisfaction/dissatisfaction].

A survey was conducted to examine what the public expects of pharmacists. We created 26 questions based on 26 different situations that patients encounter at pharmacies in order to assess patient satisfaction/dissatisfaction. Some questions were designed to compare pairs of symmetrical situations. The survey was carried out in February and March 2001. The surveys were conducted with patients and/or patients' relatives who brought their prescriptions to pharmacies and with employees of pharmaceutical companies and their family members. A factor analysis extracted two factors among the 26 variables, the first being patient dissatisfaction and the second being patient satisfaction. However, factor loadings for some paired situations were not necessarily symmetrical and thus the absolute values of the scores were not equal. The results suggest that satisfaction on one side does not entail dissatisfaction on the other side and thus satisfaction and dissatisfaction can be examined as separate and distinct entities. Based on these results, we classified pharmaceutical services into two types. The first type is referred to as instrumental service. In this situation patients do not feel great satisfaction even if such service is provided. However, they feel great dissatisfaction if the service is not provided. The second type is referred to as expressive service. These patients feel some satisfaction if such service is provided, however, they do not feel a fatal dissatisfaction if the service is not provided. Our research documents that when examining data based on the assumption that there is a different dimensionality for patient satisfaction and dissatisfaction, it is possible to gain insights into new aspects of pharmaceutical services that are otherwise impossible to assess.

Adolescent↗

PubMed2005

Kinetics of delayed chlorophyll a fluorescence registered in milliseconds time range.

Delayed fluorescence dark decays in the time interval from 0.35 to 5.5 ms are measured during dark to light adaptation in whole barley leaves and isolated thylakoid membranes, using a disc phosphoroscope. The changes in delayed fluorescence features are compared with variable chlorophyll fluorescence simultaneously registered with the same apparatus as well as in parallel by Handy PEA (Hansatech Instruments Ltd.), and absorbance changes at 820 nm. The registered delayed fluorescence signal is a sum of three components - submillisecond with lifetime of about 0.6 ms, millisecond decayed 2-4 ms and slow component with lifetime > >5.5 ms. The submillisecond delayed fluorescence component is proposed to be a result of radiative charge recombination in Photosystem II reaction centers in the state Z+PQA -QB -, and its lifetime is determined by the rate of electron transfer from QA - to QB -. The millisecond delayed fluorescence component is associated with recombination in Z+PQA -QB = centers with a lifetime determined by the sum of the rate constants of electron transfer from the oxygen-evolving complex to Z+ and of the exchange between the reduced and oxidized plastoquinone pool in the QB-site. On the basis of these assumptions and of the different share of the three components in the integral delayed fluorescence during induction, an attempt has been made to interpret the changes in the delayed fluorescence intensity during the transition of the photosynthetic apparatus from dark to light adapted state.

Chlorophyll↗

PubMed1995

Risk assessment of environmentally influenced airway diseases based on time-series analysis.

Threshold values are of prime importance in providing a sound basis for public health decisions. A key issue is determining threshold or maximum exposure values for pollutants and assessing their potential health risks. Environmental epidemiology could be instrumental in assessing these levels, especially since the assessment of ambient exposures involves relatively low concentrations of pollutants. This paper presents a statistical method that allows the determination of threshold values as well as the assessment of the associated risk using a retrospective, longitudinal study design with a prospective follow-up. Morbidity data were analyzed using the Fourier method, a time-series analysis that is based on the assumption of a high temporal resolution of the data. This method eliminates time-dependent responses like temporal inhomogeneity and pseudocorrelation. The frequency of calls for respiratory distress conditions to the regional Mobile Medical Emergency Service (MMES) in the city of Leipzig were investigated. The entire population of Leipzig served as a pool for data collection. In addition to the collection of morbidity data, air pollution measurements were taken every 30 min for the entire study period using sulfur dioxide as the regional indicator variable. This approach allowed the calculation of a dose-response curve for respiratory diseases and air pollution indices in children and adults. Significantly higher morbidities were observed above a 24-hr mean value of 0.6 mg SO2/m3 air for children and 0.8 mg SO2/m3 for adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2006

Variable populations within variable populations: quantifying mitochondrial heteroplasmy in natural populations of the gynodioecious plant Silene vulgaris.

Populations of mitochondria reside within individuals. Among angiosperms, these populations are rarely considered as genetically variable entities and typically are not found to be heteroplasmic in nature, leading to the widespread assumption that plant mitochondrial populations are homoplasmic. However, empirical studies of mitochondrial variation in angiosperms are relatively uncommon due to a paucity of sequence variation. Recent greenhouse studies of Silene vulgaris suggested that heteroplasmy might occur in this species at a level that it is biologically relevant. Here, we use established qualitative methods and a novel quantitative PCR method to study the intraindividual population genetics of mitochondria across two generations in natural populations of S. vulgaris. We show incidences of heteroplasmy for mitochondrial atpA and patterns of inheritance that are suggestive of more widespread heteroplasmy at both atpA and cox1. Further, our results demonstrate that quantitative levels of mitochondrial variation within individuals are high, constituting 26% of the total in one population. These findings are most consistent with a biparental model of mitochondrial inheritance. However, selection within individuals may be instrumental in the maintenance of variation because S. vulgaris is gynodioecious. Male sterility is, in part, regulated by the mitochondrial genome, and strong selection pressures appear to influence the frequency of females in these populations.

Genetic Variation↗

PubMed1986

Childhood relationships, adult coping resources and depression.

Underlying the design of most adult epidemiologic stress-distress studies is the assumption that only social factors deriving from individuals' current environments or very recent pasts impact on their mental health status. The present study examined the link between perceived early parent-child relations and adult depressive symptomatology. It was hypothesized that perceived dysfunctional early parent-child relationships correlate with adult depressive symptomatology and adult internal personality resources (level of autonomy-dependency and internal-external locus of control) mediate this relationship. A cohort of students beginning medical school was administered self-report questionnaires measuring the above variables (final N = 153, 73% response rate). Using correlational and regression analysis, hypothesis 1 was supported and hypothesis 2 was partially supported. The authors discuss alternative causal interpretations of the correlational findings, and recommend future studies of the social origins of psychopathology which embrace a total life cycle model. These studies should ideally reflect interdisciplinary theoretical perspectives and encompass long-term prospective research designs or greater attention to the construction and validation of instruments for improved retrospective assessments.

Adaptation, Psychological↗

PubMed1991

Stochastic microenvironment models for air pollution exposure.

Exposure assessment is a crucial link in air pollution risk assessment and management. With the recent advances in instrumentation, it has become possible to measure air pollution exposures in the vicinity of the individual human subjects, using either personal monitoring or microenvironment monitoring. For many important pollutants such as CO, NO2, and VOC, the air pollution exposure depends crucially on the location and activity of the individual: indoor versus outdoor, smoking versus not smoking, etc. The stochastic microenvironment models were developed to relate air pollution exposure to the location and activity. We review the two major existing models, the Cartesianization method (Duan, 1980, 1982, 1987) and SHAPE (Ott, 1981, 1982, 1984), and compare their assumptions and implications. We also propose a new model, the variance components model, which includes both Cartesianization and SHAPE as special cases. The variance components model considers both long-term average concentrations and short-term fluctuations. The Cartesianization focuses on long-term averages, while SHAPE focuses on short-term fluctuations. We propose to choose among the three models by examining the variance function which relates variability to averaging time. The theory is applied to the data collected from U.S. EPA's Washington CO Study, with the variance function estimated using Carroll and Ruppert's (1984) transform-both-sides regression model and Duan's (1983) smearing estimate. For the microenvironment in transit, both long-term averages and short-term fluctuations are important.

Air Pollution↗

PubMed1996

Evaluation of instrument error and method agreement.

Safely operating life support equipment and evaluating new technology both require some basic understanding of measurement theory. Measurement errors fall into two main categories: systematic errors (predictable problems usually due to calibration) and random errors (unpredictable). These two types of errors can be quantified by experiments involving repeated measurements of standards or "true" values. Systematic error (called bias) is usually expressed as the mean difference between measured and true values. Random error, called imprecision, can be expressed as the standard deviation of measured values. Total error can be expressed as an error interval, being the sum of bias and some multiple of imprecision. An error interval is a prediction about the error of some proportion of future measurements (e.g., 95%) at some level of confidence (e.g., 99%) based on the variability of the sample data and the sample size. Specifically, a tolerance interval gives an estimate of the true value of some variable given repeated measurements with an assumed valid measurement system. An inaccuracy interval predicts the validity of a measurement system with an estimate of the difference between measured true values (given that a standard or true value is available for measurement). An agreement interval evaluates whether or not one measurement system (e.g., a known valid system) can be used in place of another (e.g., a new unknown system). Statistical analyses such as correlation and linear regression are commonly seen in the literature, but not usually appropriate for evaluation of new equipment. Instrument performance evaluation studies should start out with a decision about the level of allowable error. Next, experiments are designed to obtain repeated measurements of known quantities (inaccuracy studies) or of unknown quantities by two different measurement systems (i.e., agreement studies). The first step in data analysis is to generate scatter plots of the raw data for review of validity (e.g., outliers). The next step is to make sure the data adhere to the assumption of normality. The third step is to calculate basic descriptive statistics, such as the mean and standard deviation. Finally, the data should be presented in graphic form with the differences plotted against the reference values and including numerical values for the calculated error intervals. The key idea to remember is that device evaluation and method agreement studies are based on the desire to know how much trust we should place in single measurements that may be used to make life support decisions.

Bias↗