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PubMed2002

How to avoid spurious cluster validation? A methodological investigation on simulated and fMRI data.

This paper presents an evaluation of a common approach that has been considered as a promising option for exploratory fMRI data analyses. The approach includes two stages: creating from the data a sequence of partitions with increasing number of subsets (clustering) and selecting the one partition in this sequence that exhibits the clearest indications of an existing structure (cluster validation). In order to achieve that the selected partition is actually the best characterization of the data structure, previous studies were directed to find the most appropriate validity function(s). In our analysis protocol, we first optimize the sequence of partitions according to the given objective function. Our study showed that an insufficient optimization of the partition, for one or more numbers of clusters, can easily yield a spurious validation result which, in turn, may lead the analyst to a misleading interpretation of the fMRI experiment. However, a sufficient optimization, for each included number of clusters, provided the basis for a reliable, adequate characterization of the data Furthermore, it enabled an adequate evaluation of the validity functions. These findings were obtained independently for three clustering algorithms (representing the hard and fuzzy clustering variant) and three up-to-date cluster validity functions. The findings were derived from analyses of Gaussian clusters, simulated data sets that mimic typical fMRI response signals, andreal fMRI data. Based on our results we propose a number of options of how to configure improved clustering tools.

Algorithms↗

PubMed1998

Validating new toxicology tests for regulatory acceptance

Before a new or revised toxicology test is considered acceptable for safety evaluation of new substances, the test users and the industrial and regulatory decision makers must feel comfortable with it, and the decisions it supports. Comfort with, and the acceptance of, a new test comes after knowing that it has been validated for its proposed use. The validation process is designed to determine the operational characteristics of a test, that is, its reliability and relevance, in addition to its strengths and limitations. The reliability of a test is measured by its reproducibility. Its relevance is judged by its mechanistic relationship to the health effects of concern, and its ability to predict or identify those effects. The U.S. government has recently formed the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) to work with federal agencies and test developers to coordinate the evaluation and adoption of new test methods. The ICCVAM will provide guidance to agencies and other stakeholders on criteria and processes for development, validation, and acceptance of tests; coordinate technical reviews of proposed new tests of interagency interest; facilitate information sharing among agencies; and serve as an interagency resource and communications link with parties outside of the federal government on matters of test method validation. Copyright 1998 Academic Press.

Journal Article↗

PubMed1992

The validity of the MIMIC (Multiple Indicators/MultIple Causes) health index--some empirical evidence.

This study evaluates the potential of econometric models with latent (unobservable) variables for measuring health or health impairment due to a specific disease. A MIMIC disability index is estimated for a sample of 145 adults with chronic bronchitis, expressing their self-reported disability caused by the disease on a one-dimensional scale. The index is determined up to a linear transformation. Disability is thus measured on an interval scale. The data were collected by interviews. The questionnaire used for this purpose is based on a number of in-depth interviews with selected bronchitis patients conducted beforehand. The study therefore focuses directly on the patients' perceptions of their disease. The validity of the index is evaluated in three different ways. First, construct validity is assessed performing groupwise analysis and testing for differences in the index values by subgroup. To a large extent, the index is consistent with a priori expectations. Therefore, we conclude that it has high construct validity. Second, validity of the index is assessed by comparing its results to a direct rating scale produced by 21 physicians with various medical backgrounds. The MIMIC index turns out to be related in a systematic, but nonlinear way to this direct rating scale. This can be interpreted in two different ways. If one accepts the preferences of health providers as the ultimate yardstick when it comes to ranking health or chronic states the result suggests that the MIMIC index estimated in this way is not a valid measure of treatment success. By contrast, if patients' preferences are considered to be decisive, it suggests that physician-based ratings should be substituted for or at least complemented with patient-based indices (such as the MIMIC disability index estimated here) when evaluating medical services in terms of cost-effectiveness. Third we explore the extent to which the MIMIC index reflects utility associated with different states of disability, using a modified Torrance Standard Gamble approach. The above-mentioned physicians are used as experts in this procedure. The results indicate that the MIMIC index as estimated here is related in a systematic, but nonlinear way to the Standard Gamble risk index as well. The fact that this relationship is nonlinear indicates that the MIMIC index does not measure utility as derived from the experts' preferences directly. How this index would fare compared to a Standard Gamble risk index provided by patients (bronchitis subjects) is a question which remains open.(ABSTRACT TRUNCATED AT 400 WORDS)

Attitude to Health↗

PubMed1977

Validity of the W170 test for predicting maximal oxygen intake.

Recent research has related pedalling frequency to perceived exertion, indicating that subjects pedalling at higher frequencies tend to perceive lower levels of exertion. If tests administered at higher pedalling speeds are valid, then more accurate data on extremely low fit individuals might be possible. The purpose of this study was to determine the validity of the Wahlund-Sjostrand W170 test administered at 50 and 80 rpm. Maximal oxygen intake was determined for thirty male volunteer college students using standard open-circuit techniques. W170 tests were administered at 50 and 80 rpm using standard test protocol. The results indicated a differential effect of pedalling speed upon the validity of the W170 tests. Validity coefficients of rxy = 0.73 and rxy = 0.64 were found for the 50 and 80 rpm tests, respectively. Maximal oxygen intake predicted from the W170 test administered at 80 rpm was significantly different from both the criterion maximal oxygen intake and the W170 prediction at 50 rpm. This difference was attributed to a significantly higher heart rate response to 80 rpm tests at the lower workload of 600 kpm/min. It was concluded that more valid W170 tests are attained at the conventional pedalling speed of 50 rpm.

Adult↗

PubMed1984

The validity of animal models of depression.

Eighteen animal models of depression are reviewed in relation to three sets of validating criteria. Of the 18 models, five could only be assessed for predictive validity, seven could be assessed for predictive and face validity, and six could potentially have predictive, face and construct validity. Some traditional models (reserpine reversal, amphetamine potentiation) are rejected as invalid; the models with the highest overall validity are the intracranial self-stimulation, chronic stress and learned helplessness models in rats, and the primate separation model.

5-Hydroxytryptophan↗

PubMed1984

Convergent validity of type A behavior pattern scales and their ability to predict physiological responsiveness in a sample of female public employees.

The purpose of this study was to assess the construct validity of the structured interview (SI), Jenkins Activity Survey (JAS), Thurstone Activity Scale, and Bortner Type A Scale in a sample of female employees from a government service agency. Criteria for validity assessment were physiological reactance to a mental stressor, psychological strains experienced at work, physical symptoms associated with work, and urinary catecholamine production at work. A continuous Type A SI scale demonstrated better convergent and construct validity than did the SI category scores. All of the SI Type A scales were reliable. Among the questionnaire measures only the Thurstone Activity Scale was reliable and showed the strongest construct validity. The SI measures of Type A tended to correlate with physiological responsiveness (changes in heart rate, skin temperature, and skin conductance), while the questionnaire measures correlated with self-reports of job strains (satisfaction, irritation, depression, physical symptoms), thus indicating the operation of measurement artifacts in validity assessment. No significant correlations were obtained between Type A and catecholamines. Comparison of correlation analysis with subgroup analysis revealed the former to be a more powerful test of the relationships that may exist between Type A behavior pattern and relevant criteria.

Adult↗

PubMed1991

The ecological validity of laboratory and analogue assessment methods of ADHD symptoms.

An important question in the attempt to generalize laboratory findings on attention deficit-hyperactivity disorder (ADHD) children to clinical issues concerning their assessment, diagnosis, outcome, and treatment response is the ecological validity of the commonly used tasks and analogue behavioral observation procedures. This paper examines the concept of ecological validity and issues inherent in its evaluation. The evidence from a variety of sources is then reviewed on the relationship between laboratory methods of assessing inattention, impulsivity, and overactivity and measures of these same constructs in natural settings. Additional findings pertaining to this issue from a recent study of 140 ADHD and normal children and 159 ADHD and normal adolescents using a multimethod battery of tests are also reported. In general, the ecological validity of most methods is of a low to moderate degree, with some traditional laboratory tasks proving unsatisfactory. A few tasks demonstrated acceptable degrees of ecological validity but even these require improvement. It is concluded that future advances in ecological validity are likely to come from: (a) a greater reliance on assessments of the target behaviors in natural settings and (b) combining several of the more promising tasks and analogue methods into a battery that is taken over longer time intervals than has been customary and averaged across repeated administrations.

Attention Deficit Disorder with Hyperactivity↗

PubMed2000

[Validity and reliability of proband recall of fractures].

The validity and reliability of patient recall of diseases depends on the kind of disease. The validity and reliability of patients' recall of fractures was assessed among the 146 cases of a nested case-control study on independent living following fractures in the elderly. On declaration of a fracture a letter was sent to the general practitioner requesting medical information on the latest fracture receiving treatment. A total of 99 medical discharge letters (68%) could be collected for further evaluation. The information on fracture localisation which was obtained both during the patients interviews 1994/95 and 1998 and through the medical discharge letters were coded with reference to the AO (Arbeitsgemeinschaft für Osteosynthesefragen)-classification and compared. The Kappa-statistic for the reliability of patient information was 0.80-0.89, and 0.77-0.89 for the validity, depending on the degree of specified concordance. Obtaining information on fractures from patients appears as a valid and reliable source of epidemiologic data. Patients who generally are affected physically or had to stay in a hospital due to a fracture or its treatment seem to have a good recall of this event. It appears that it can be remembered years after the event with sufficient reliability and validity.

Aged↗

PubMed1992

Behavioral screening for cognition enhancers: from indiscriminate to valid testing: Part I.

Preclinical efforts to detect and characterize potential cognition enhancers appear to have been dominated by a strategy of demonstrating a wide variety of apparently beneficial behavioral effects with little attention given to the specific psychological mechanisms underlying behavioral enhancement. In particular, the question of whether or not behavioral facilitation is based on relevant mnemonic mechanisms and is independent of the stimulus properties and/or the motivational and attentional components of a task is not often considered. As a result, an overwhelming number of compounds have failed to produce the clinical effects predicted for them on the basis of preclinical research. The available data suggest that a more successful approach requires deductive research strategies rather than the indiscriminate accumulation of apparently beneficial effects in a variety of behavioral tasks and animal models. The first step towards such an approach is a systematic and rigorous evaluation of the different aspects of validity for the models most frequently used in preclinical research. It is concluded that a combination of good construct validity and good face validity represents a necessary condition for screening tests with predictive validity, and that the most popular paradigms fail to fulfil these criteria. Future screening programs for cognition enhancers will probably be characterized by a depreciation of "fast and dirty tests" in favor of approaches focussing on the validity of the effects of potential cognition enhancers.

Animals↗

PubMed1995

Rapid classification of positive blood cultures: validation and modification of a prediction model.

OBJECTIVE: 1) To validate a previously developed prediction model to aid physicians in differentiating true positive blood cultures from contaminants when the laboratory first calls with a positive result, and 2) to determine whether it could be modified to make it more practical for clinical use without altering predictability. DESIGN: A prospective cohort study of hospitalized patients (validation set) who had blood cultures done over a two-month period. Data collected included the seven independent predictors in the rapid classification of positive blood cultures model. The model was modified by eliminating one of the predictors (which required clinical data) but maintaining the laboratory components (morphologic and Gram stain characteristics, number of bottles positive, and time to positivity). The "blood culture episode" was the unit of evaluation. A blood culture episode was defined as a 48-hour period beginning with the drawing of blood for the culture and included any blood cultures obtained during that time period. Receiver operating characteristic (ROC) curve analysis was used to compare the predictabilities of these models. SETTING: A 550-bed, university-affiliated county hospital that is a regional trauma center and has the only burn treatment unit in the region. PATIENTS: All adult (> or = 16 years old) patients who had blood cultures done during the study period were eligible. Only patients with positive blood cultures were included in the study. INTERVENTIONS: None. MAIN RESULTS: Of 559 blood culture episodes identified, 139 (25%) included the growth of one or more organisms; 62 (45%) of the 139 episodes represented true bacteremia. By ROC curve analysis, there was no significant difference in the mean areas under the curve (AUCs) (+/- SE) of the model in the derivation set (the previously developed model) (0.93 +/- 0.02) compared with the validation set (0.89 +/- 0.03; p = 0.29). In the validation set there was no significant difference in the mean AUCs when the model was modified (0.89 +/- 0.03) by removing the clinical component vs the unmodified model (0.89 +/- 0.03; p = 0.98). CONCLUSIONS: The rapid classification of blood cultures model was validated in a general hospital population. Predictability of the model was not altered significantly by eliminating one component that required clinical data. Because the modified model requires only laboratory information, this may allow reporting of the probability of true bacteremia at the time a positive blood culture is initially reported to physicians. This information may aid physicians in interpreting the positive blood culture.

Adult↗

PubMed1993

Framework for validation and implementation of in vitro toxicity tests.

The development and application of in vitro alternatives designed to reduce or replace the use of animals, or to lessen the distress and discomfort of laboratory animals, is a rapidly developing trend in toxicology. However, at present there is no formal administrative process to organize, coordinate, or evaluate validation activities. A framework capable of fostering the validation of new methods is essential for the effective transfer of new technologic developments from the research laboratory into practical use. This committee has identified four essential validation resources: chemical bank(s), cell and tissue banks, a data bank, and reference laboratories. The creation of a Scientific Advisory Board composed of experts in the various aspects and endpoints of toxicity testing, and representing the academic, industrial, and regulatory communities, is recommended. Test validation acceptance is contingent on broad buy-in by disparate groups in the scientific community--academics, industry, and government. This is best achieved by early and frequent communication among parties and agreement on common goals. It is hoped that the creation of a validation infrastructure composed of the elements described in this report will facilitate scientific acceptance and utilization of alternative methodologies and speed implementation of replacement, reduction, and refinement alternatives in toxicity testing.

In Vitro Techniques↗

PubMed1997

The relationship of patient-administered outcome assessments to quality of life and physician ratings: validity of the BASIS-32.

The reliability and validity of a patient-administered version of the Behavior and Symptom Identification Scale (BASIS-32) was compared to the original interviewer-administered version. The construct validity of BASIS-32 subscales was assessed by examining their relationship with functional and satisfaction quality of life and physician ratings of functional and clinical status. A total of 361 acute psychiatric inpatients were given a self-administered BASIS-32, nurse-administered Lehman's Quality of Life Interview (QOLI), and Psychiatrist Assessment Form at admission and discharge. The original factor structure, internal consistency reliability, discriminant validity, and sensitivity to change were replicated. The patient-administered BASIS-32 is equally as reliable and valid as the interview. Construct validity analyses revealed that functional and satisfaction QOLI indices were moderately related to the BASIS-32 in the hypothesized directions. All satisfaction scales were associated with significantly less severity. Physician ratings were only mildly related to the subscales. The BASIS-32 used in outcome assessments with inpatients provides important and unique perspectives on functional and clinical status that are not tapped by clinician-rated assessments.

Inpatients↗

PubMed2004

[Cardiovascular risk assessment for informed decision making. Validity of prediction tools].

BACKGROUND AND PURPOSE: Patient involvement in health care decisions is increasingly requested. The authors investigated whether currently available assessment tools for prediction of cardiovascular risk can be used for individual risk prediction as a basis of informed decision making. METHODS: The authors searched for risk assessment tools and respective validation studies in Medline (until August 16, 2004) and the Cochrane Library (issue 2/2004). The following criteria were used for evaluation of prognostic studies: (1) discrimination between risk groups; (2) predictive values; (3) prognostic agreement; (4) transferability across populations. RESULTS: A total of twelve assessment tools were identified. The Framingham function, Sheffield Tables, Canadian Tables, Framingham Categorial, New Zealand, Joint British, and European Charts (1994 and 1998) are based on the Framingham Study; PROCAM Risk Score, UKPDS Risk Engine, and SCORE Risk Charts use different source data. Framingham-based instruments overestimate cardiovascular risk of Central-European populations by at least 30%, with substantial regional variation even within a country (between 30% and 100%, British Regional Heart Study). Therefore, prior to application the assessment tools would need recalibration using regional data of cardiovascular mortality and adjustment for social class differences. Published sensitivity, specificity, and C-statistics for external validation (area under the curve [AUC] approximately 0.6) are clearly inferior to internal validation (AUC approximately 0.8). Agreement between instruments beyond chance is moderate (kappa approximately 0.5). No studies on external validation could be identified for the new European SCORE Risk Charts and UKPDS Risk Engine. CONCLUSION: Validation of currently available assessment tools for cardiovascular risk prediction is inadequate. Uncritical use may lead to substantial under- or overestimation of individual cardiovascular risk and inappropriate treatment decisions.

Adult↗

PubMed2005

Occupational abilities and performance scale--reliability-validity assessment factor analysis.

BACKGROUND: This article presents a study of the Occupational Abilities and Performance Scale (OAPS), developed for administration to schizophrenic patients. The reliability and validity of the OAPS has been evaluated. METHOD: A total of 174 schizophrenic patients who participated in the Psychosocial and Vocational Rehabilitation Unit (PVRU) of the University Mental Health Research Institute (UMHRI) in Athens were assessed. The OAPS is conducted at entry and after 18 months, when the client has completed training. RESULTS: The results of the reliability analysis showed very good internal consistency, with high split-half reliability as well as test-retest reliability and inter-rater agreement. The scale was also found to have good predictive validity, as well as concurrent validity. Finally, factor analysis with principal components extraction method was performed in order to assess the construct validity of the scale. CONCLUSIONS: The results of factor analysis supported the conclusion of good reliability and validity of the OAPS and revealed the existence of five components, each correlated with a set of the original items.

Adult↗

PubMed2003

Validation of the multiple organ dysfunction (MOD) score in critically ill medical and surgical patients.

OBJECTIVE: To validate the Multiple Organ Dysfunction (MOD) score externally. DESIGN: Prospective observational cohort study. SETTING: Mixed medical/surgical ICU in a tertiary referral university hospital. PATIENTS AND PARTICIPANTS: Thousand eight hundred and nine patients admitted to ICU for more than 24 h over a 3-year period. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The MOD score was calculated daily for all patients. The criterion validity of the individual organ scores, the maximal MOD score and the change in MOD score were assessed by examining the relationship between increasing scores and ICU mortality. Increased maximal MOD scores and each of the six individual organ scores, and change in MOD scores were associated with increased mortality. CONCLUSIONS: Maximal and individual organ scores have criterion validity when tested in a different ICU from that in which the scores were derived, indicating that the scoring systems are reproducible. The association of change in MOD score with mortality indicates that the score is responsive. These data, combined with previous data establishing concept and content validity, indicate that the MOD score is a valid measure of multi-organ dysfunction.

Critical Care↗

PubMed1997

Validity, reliability and utility of the chronic mild stress model of depression: a 10-year review and evaluation.

This paper evaluates the validity, reliability and utility of the chronic mild stress (CMS) model of depression. In the CMS model, rats or mice are exposed sequentially, over a period of weeks, to a variety of mild stressors, and the measure most commonly used to track the effects is a decrease in consumption of a palatable sweet solution. The model has good predictive validity (behavioural changes are reversed by chronic treatment with a wide variety of antidepressants), face validity (almost all demonstrable symptoms of depression have been demonstrated), and construct validity (CMS causes a generalized decrease in responsiveness to rewards, comparable to anhedonia, the core symptom of the melancholic subtype of major depressive disorder). Overall, the CMS procedure appears to be at least as valid as any other animal model of depression. The procedure does, however, have two major drawbacks. One is the practical difficulty of carrying out CMS experiments, which are labour intensive, demanding of space, and of long duration. The other is that, while the procedure operates reliably in many laboratories, it can be difficult to establish, for reasons which remain unclear. However, once established, the CMS model can be used to study problems that are extremely difficult to address by other means.

Animals↗

PubMed2003

Validity of performance indicators for assessing prescribing quality: the case of asthma.

OBJECTIVES: The aim of this study was to assess the concurrent validity between the identification of sub-optimal treatment based on clinical information and computer generated indicators. Indicators that are associated with sub-optimal treatment in one of the four steps of asthma management were assessed. DESIGN: The ability of each indicator to identify patients with sub-optimal asthma treatment from computerised general practitioner (GP) prescription records was assessed by comparing them with the results of an individual patient assessment using clinical data. SETTING: Chronic asthma patients ( n=146) registered with 16 Dutch GPs. MAIN MEASURES: The sensitivity and positive predictive value (PPV) of each performance indicator was determined. RESULTS: The step-1 indicator, focusing on patients not prescribed a short-acting beta-agonist, had an acceptable sensitivity (0.86), but a low PPV (0.52). The two step-2 indicators, targeting under-prescription of inhaled corticosteroids, had sensitivities of 0.74 and 0.37 and PPVs of 0.46 and 0.71, respectively. The step-3 indicator, which targeted under-dosing of inhaled corticosteroids, had a sensitivity of 0.07 and a PPV of 0.2. The fourth indicator, focusing on under-prescription of long-acting beta-agonists, could not be validated due to inadequate numbers of patients with severe asthma in our study sample. DISCUSSION: None of the indicators investigated was considered valid for assessing prescriber performance, despite having good face and content validity. Performance indicators that have not been validated can only provide a broad-brush approach for assessing prescribing quality and should be used with extreme caution.

Adolescent↗

PubMed2003

Validation of a German version of the 'Disabilities of Arm, Shoulder and Hand' questionnaire (DASH-G).

OBJECTIVE: In 1994 the American Academy of Orthopedic Surgeons' outcome research committee developed and validated a functional outcome questionnaire for disabilities of the upper extremity (DASH). The objective of our study was to translate the DASH into German and to evaluate its reliability and validity for German-speaking patients with shoulder pain. METHODS: Translation-backtranslation of the DASH was performed according to published guidelines. Psychometric properties and validity were assessed in 49 consecutive patients with shoulder pain originating from within the shoulder girdle. Age, duration of symptoms and current pain were obtained. Test-retest reliability was assessed in a subset of 18 patients who filled in the questionnaire 10 days later. Internal consistency was evaluated with Cronbach's alpha coefficient. Test-retest reliability was assessed using Spearman correlations and the Bland and Altman plot. To study the validity, we examined the correlation of the DASH with other measures of function of the upper extremity including the HAQ subscales relating to the upper extremity and pain measures (e.g. numerical rating scale, SF-36 pain scale). We also examined our hypothesis that the DASH is moderately correlated with measures of range-of-motion (e.g., forward flexion and abduction). RESULT: Translation-backtranslation revealed no major difficulties. The mean age of the patients was 59 years, mean duration of symptoms 60 months and current pain score 5.6 (NRS). Test-retest reliability was 0.90 for the total DASH. The internal consistency was 0.96. Strong correlations (p<0.01) were found between the DASH and the mean among the five subscales of the HAQ representing upper extremity function (0.88) and pain as measured with the SF-36 bodily pain scale (-0.79). As hypothesized, the DASH was also moderately correlated with measures of range-of-motion (e.g. forward flexion rho=-0.49; abduction rho=-0.57). CONCLUSION: Our data confirm that the German version of the DASH retains the characteristics of the American original and is a reliable and valid instrument to measure functional disability in German speaking patients with shoulder pain.

Adult↗