Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “instrumental variable”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29Linked to original sources
PubMed2001

Stroke care: a method for measuring compliance with AHCPR guidelines.

The purpose of this article is to describe a method for converting practice guidelines to measurement criteria. To evaluate the processes of care received by patients with stroke at 11 Veteran's Administration hospital sites, we developed a measurement system based on Agency for Health Care Policy and Research (AHCPR) Post-Stroke Rehabilitation Clinical Practice Guidelines. Guideline recommendations were used as the framework for identifying important dimensions of care, and for developing chart abstraction instruments for both the acute and postacute settings. Using a modified Delphi technique to solicit opinions from an expert panel, a method was developed for aggregation of item-level chart abstraction components to overall guideline compliance scores. The measurement system was shown to have good-to-excellent intrarater and interrater reliability at the item, dimension, and overall compliance score levels. Abstraction of a sample of 100 medical records demonstrated the ability of the instruments to detect variability in processes of post-stroke care. This study provides the foundation for future research, which will evaluate associations between processes of post-stroke care, as measured by this medical chart abstraction system, and patient outcomes. (All abstraction instruments, criteria, and scoring algorithms described in this article are available for download at http://www2.kumc.edu/coa.)

Aged↗
PubMed1982

Error analysis for the determination of cerebral blood flow with the continuous inhalation of 15O-labeled carbon dioxide and positron emission tomography.

The inhalation of C15O2 can be used for determining local cerebral blood flow (LCBF) using a quantitative model. The determination of LCBF in three dimensions using positron emission tomography (PET) involves errors due to counting statistics, data manipulation, and the estimation of parameters in the mathematical model. This work examines error propagation and its relation to the radiation dose to the subject's lungs. An expression has been derived for the root mean square uncertainty in LCBF as a function of LCBF, the spatial resolution and the sensitivity of PET instrument, the normal variability in the brain-blood partition coefficient for water, and absorbed radiation dose to the subject's lungs. The error in LCBF increases as CBF increases. At a normal cortical LCBF of 80 ml/100 g-m and a PET instrument with a 1.65 cm FWHM resolution, and a 46,000 cps per microCi/g sensitivity per slice, an error (coefficient of variation) of 5% results from an inhaled activity of 250 mCi, resulting in a lung dose of 5 rads, the maximum permissible dose allowed. For a more acceptable dose of 1.2 rads, the error is 7%. At a higher resolution (0.8 cm FWHM) and lower sensitivity (15,000 cps per microCi/g per slice), errors become on the order of 28% for a lung dose of 1.2 rads. Errors due to other factors such as blood sample counting, and instrument cross calibration can be virtually eliminated by proper technical strategies. This consideration of error and its relation to radiation dose is important for the application of this inhalation technique for the quantification of LCBF.

Administration, Intranasal↗
PubMed1991

Inherent variability in the power output of endosonic instruments.

The displacement amplitude of endosonic files was measured with the aid of light microscopy in order to determine the power output of different ultrasonic units. The results showed that there was a substantial difference in the displacement amplitudes when the same size of file was used in different ultrasonic units made by the same or different manufacturers. File fracture was found to be a problem when files were driven at high displacement amplitudes.

Dental Cavity Preparation↗
PubMed2004

Measures of clinical severity, quality of life, and psychological distress in patients with psoriasis: a cluster analysis.

The impact of psoriasis on patients' quality of life may be quite destructive, and measures of disease status alone seem to have questionable validity in describing the true burden of illness. Our aim was to study, in patients with psoriasis, the relationship between classical measures of clinical status (i.e., PASI and SAPASI) and quality-of-life indexes (i.e., Skindex-29, Dermatology Life Quality Index, Psoriasis Disability Index, Impact of Psoriasis Questionnaire). In addition, two psychological distress indexes (i.e., Psoriasis Life Stress Inventory, 12-item General Health Questionnaire) were assessed. Data were collected between February 2000 and July 2001 at the inpatient wards of the Dermatological Institute IDI-IRCCS, Rome, Italy, in the framework of a large project on clinical, epidemiologic, emotional, and quality-of-life aspects of psoriasis. A cluster analysis of all the above-mentioned instruments was conducted on 786 eligible patients hospitalized with a diagnosis of psoriasis. Correlations between instruments were also analyzed in subsets of patients based on the main variables of interest. The instruments clustered in two distinct groups, one formed by clinical severity measurements and the other grouping all the quality-of-life and psychological indexes. The correlations between instruments observed in the subgroups determined by different sociodemographic and clinical variables showed the same pattern. In conclusion, the dissimilarity between clinical severity assessment and patient-centered measures stresses the need for a more comprehensive assessment of severity of psoriasis.

Adult↗
PubMed1996

Measurement algorithm accuracy of the RVG-PCi in vertical and diagonal assessments at various beam energies.

The Trophy RadioVisioGraphy model PCi was compared to Kodak Ektaspeed Plus film for accurate recording and estimation of the length of size 15 files placed vertically and diagonally across the receptor surface. Variations in kilovoltage (50, 70, and 75) and exposure were also factored. Eight observers estimated file lengths using the proprietary software measurement algorithm for the RVG-PCi and a millimeter rule for the film-based radiographs. Both modalities resulted in slight magnification for vertically oriented files; however, the RVG-PCi caused overestimation in the order of 6 to 8% with diagonally oriented instruments. Measurement interobserver variability was least when using the RVG-PCi. It was concluded that the proprietary software supplied with RVG-PCi is not sufficiently accurate for endodontic assessment. Furthermore, exposures above 0.15 s at 75 kVp resulted in pixel saturation resulting in apparent shortening of the instrument; hence, length calculations are particularly sensitive to overexposure when using the RVG-PCi.

Algorithms↗
PubMed2005

Patient-focused measures of functional health status and health-related quality of life in pediatric orthopedics: a case study in measurement selection.

The objectives of this report are to review the assessment of patient-focused outcomes in pediatric orthopedic surgery, to describe a framework for identifying appropriate sets of measures, and to illustrate an application of the framework to a challenging orthopedic problem.A detailed framework of study design and measurement factors is described. The factors are important for selecting appropriate instruments to measure health status and health-related quality of life (HRQL) in a particular context. A study to evaluate treatment alternatives for patients with neurofibromatosis type 1 and congenital tibial dysplasia (NF1-CTD) provides a rich illustration of the application of the framework. The application involves great variability in the instrument selection factors. Furthermore, these patients and their supportive caregivers face numerous complex health challenges with long-term implications for HRQL. Detailed summaries of important generic preference-based multi-attribute measurement systems, pediatric health profile instruments, and pediatric orthopedic-specific instruments are presented. Age-appropriate generic and specific measures are identified for study of NF1-CTD patients. Selected measures include the Activities Scale for Children, Gillette Functional Assessment Questionnaire Walking Scale, Health Utilities Index, and Pediatric Inventory of Quality of Life. Reliable and valid measures for application to pediatric orthopedics are available. There are important differences among measures. The selected measures complement each other. The framework in this report provides a guide for selecting appropriate measures. Application of appropriate sets of measures will enhance the ability to describe the morbidity of pediatric orthopedic patients and to assess the effectiveness of alternative clinical interventions. The framework for measurement of health status and HRQL from a patient perspective has relevance to many other areas of orthopedic practice.

Activities of Daily Living↗
PubMed1988

Identifying the variables maintaining self-injurious behavior.

Reliability and validity data are reported for an instrument designed to identify variables maintaining self-injurious behavior. The Motivation Assessment Scale (MAS) is a 16-item questionnaire that addresses the situational determinants of self-injurious behavior in persons with autism and other developmental disorders. The reliability study indicated that teachers of 50 developmentally disabled persons could agree on the variables presumably maintaining their student's self-injury (interrater reliability), and that they would be in agreement again 30 days later (test-retest reliability). The validity study indicated that teacher's ratings on the MAS of 8 subjects' self-injury predicted how their students would behave in analogue situations. Specifically, the MAS predicted the subjects' self-injurious behavior in situations with decreased adult attention, with increased academic demands, with restricted access to tangibles, and in unstructured settings. The MAS is presented as an alternative or adjunct to more formal functional analyses in efforts to identify the variables controlling self-injurious behavior.

Adolescent↗
PubMed1985

Effect of non-surgical periodontal therapy (IV). Operator variability.

Healing following non-surgical periodontal therapy was studied and the results of instrumentation performed by 6 operators compared. Incisors, cuspids and premolars with periodontal pockets up to 11 mm deep in 20 patients were treated by plaque control and a single episode of supra- and subgingival debridement. A split-mouth approach was used to compare the participating therapists. The effects of the therapy were monitored using changes in plaque score, bleeding score, probing pocket depth and probing attachment level. Marked improvement, similar to that seen in previous studies evaluating non-surgical therapy was noted during the initial 6-9 months. No further changes of the recorded parameters could be observed during the rest of the 24-month observation period. Differences between sites treated by the various operators were negligible. Thus, it appears, that deep periodontal pockets in incisors, cuspids and premolars may be successfully treated by plaque control and 1 episode of instrumentation and that operator variability may be limited.

Adult↗
PubMed2005

[Mechatronic in functional endoscopic sinus surgery. First experiences with the daVinci Telemanipulatory System].

BACKGROUND: This study examines the advantages and disadvantages of a commercial telemanipulator system (daVinci, Intuitive Surgical, USA) with computer-guided instruments in functional endoscopic sinus surgery (FESS). METHODS: We performed five different surgical FESS steps on 14 anatomical preparation and compared them with conventional FESS. A total of 140 procedures were examined taking into account the following parameters: degrees of freedom (DOF), duration , learning curve, force feedback, human-machine-interface. RESULTS: Telemanipulatory instruments have more DOF available then conventional instrumentation in FESS. The average time consumed by configuration of the telemanipulator is around 9+/-2 min. Missing force feedback is evaluated mainly as a disadvantage of the telemanipulator. Scaling was evaluated as helpful. The ergonomic concept seems to be better than the conventional solution. DISCUSSION: Computer guided instruments showed better results for the available DOF of the instruments. The human-machine-interface is more adaptable and variable then in conventional instrumentation. Motion scaling and indexing are characteristics of the telemanipulator concept which are helpful for FESS in our study.

Clinical Competence↗
PubMedDate not supplied

Perceptions of control in adults with epilepsy.

That psychosocial problems are extant in epilepsy is evidenced by a suicide rate among epileptic persons five times that of the general population and an unemployment rate estimated to be more than twice that of the population as a whole. External perceptions of control secondary to repeated episodes of seizure activity that generalize to the social sphere have been implicated as causes of these problems. The hypothesis that individuals who continue to have seizures become more and more external in perceptions of control was tested by a survey mailed to a sample of individuals with epilepsy in a metropolitan area of the Midwest. Dependent variables were, scores on instruments measuring locus of control and attributional style. The independent variable was a measure of seizure control based on present age, age at onset, and length of time since last seizure. Gender, socioeconomic status, and certain parenting characteristics were included as control variables, as they are also known to affect perceptions of control. Analysis by multiple regression techniques supported the study's hypothesis when perceptions of control was conceptualized as learned helplessness for bad, but not for good, events. The hypothesis was not confirmed when perceptions of control was conceptualized as either general or health locus of control.

Adaptation, Psychological↗
PubMedDate not supplied

Walking and bicycling: an evaluation of environmental audit instruments.

PURPOSE: This paper reviews existing environmental audit instruments used to capture the walkability and bikability of environments. The review inventories and evaluates individual measures of environmental factors used in these instruments. It synthesizes the current state of knowledge in quantifying the built environment. The paper provides health promotion professionals an understanding of the essential aspects of environments influencing walking and bicycling for both recreational and transportation purposes. It serves as a basis to develop valid and efficient tools to create activity-friendly communities. DATA SOURCES: Keyword searches identified journal articles from the computer-based Academic Citation Databases, including the National Transportation Library, the Web of Science Citation Database, and MEDLINE. Governmental publications and conference proceedings were also searched. STUDY INCLUSION AND EXCLUSION CRITERIA: All instruments to audit physical environments have been included in this review, considering both recreation- and transportation related walking and bicycling. Excluded are general methods devised to estimate walking and cycling trips, those used in empirical studies on land use and transportation, and research on walking inside buildings. DATA EXTRACTION METHODS: Data have been extracted from each instrument using a template of key items developed for this review. The data were examined for quality assurance among three experienced researchers. DATA SYNTHESIS: A behavioral model of the built environment guides the synthesis according to three components: the origin and destination of the walk or bike trip, the characteristics of the road traveled, and the characteristics of the areas surrounding the trip's origin and destination. These components, combined with the characteristics of the instruments themselves, lead to a classification of the instruments into the four categories of inventory, route quality assessment, area quality assessment, and approaches to estimating latent demand for walking and bicycling. Furthermore, individual variables used in each instrument to measure the environment are grouped into four classes: spatiophysical, spatiobehavioral, spatiopsychosocial, and policy-based. MAJOR CONCLUSIONS: Individually, existing instruments rely on selective classes of variables and therefore assess only parts of built environments that affect walking and bicycling. Most of the instruments and individual measures have not been rigorously tested because of a lack of available data on walking and bicycling and because of limited research budgets. Future instrument development will depend on the acquisition of empirical data on walking and bicycling, on inclusion of all three components of the behavioral model, and on consideration of all classes of variables identified.

Bicycling↗
PubMedDate not supplied

Therapeutic massage in older persons: research issues.

Growing recognition of the importance of holistic nursing interventions is resulting in a revival in the use of therapeutic massage. Massage contributes to health and healing through enhancement of relaxation, and is a safe, caring, and inexpensive intervention. Therapeutic massage research using older populations is reviewed for identification of its theoretical framework, design, outcome variables, sample, procedures, instruments, analyses and results. To establish a scientific basis for therapeutic massage in the future, it is critical that nurses include the following key elements in their research studies: clear definitions: procedures for massage that include type(s) of massage performed, part of body massaged, and length of time of massage; and analyses that control for the pre-massage level of the variable of interest. Research variables need to focus on concepts that have major health consequences such as agitation, immune status, and pain.

Aged↗
PubMed2006

Variability of force magnitude and force duration in manual and instrument-based manipulation techniques.

OBJECTIVE: The goal of this study was to compare the variation of manipulative forces produced by instruments and a manual technique. METHODS: Four operators (2 experts and 2 novices) used 4 different mechanical instruments to apply force to a uniaxial load cell. A different group of 2 expert and 2 novice operators used a traditional manual technique to apply force to a sensor mat. Two primary outcome variables were obtained from each sensor system: peak-to-peak force magnitude (N) and peak-to-peak force duration (millisecond). Multiple analyses were performed to determine the absolute differences and variation in each variable. RESULTS: Force-producing instrumentation exhibited less variation in absolute force and force duration compared to manual techniques. However, the same instrument in the hands of different operators often produced significantly different values of absolute force and force duration. Although absolute values of force magnitude generally differed between operators, intraoperator variation was equal for instruments and the manual technique. Conversely, for force duration, significant differences in interoperator variability were observed for the manual technique and for one of the instruments. CONCLUSIONS: Force-producing instruments reduce absolute variation in force magnitude and duration. However, this reduction does not eliminate significant differences in absolute force parameters observed to occur between some operators using the same instrument. Given these observations, claims of instrument superiority that do not account for interoperator variability should be considered with caution.

Humans↗
PubMed1999

Gestational age related changes in cardiac dynamics of the fetal baboon.

To provide insight into the maturation of neural mechanisms governing fetal heart rate and rate variability, seven chronically instrumented fetal baboons were monitored under steady state conditions between 120 and 165 days gestation (term 175 d). Forty records of 24 h duration (5-7 records/fetus) were evaluated. For each fetus, heart rate decreased with gestational age (mean+/-SD, r = -0.530+/-0.324, P <0.05). In contrast, there were increases with age in markers of various components of autonomic control of fetal R-wave to R-wave interval (RRi) variability as reflected in a positive correlation with age for all fetuses of SD RRi (r = 0.656+/-0.347, P < 0.01), root mean squared differences in RRi (r = 0.686+/-0.223, P <0.05), and power at low frequency in the RRi spectrum (r = 0.800+/-0.161 P < 0.01). In each of the seven fetuses, scatter plots of RRi as a function of the prior RRi (Poincare plots) had increased dispersion around the median with gestational age (0.605+/-0.371, P<0.05). Additional measures of variability evaluated changes in RRi from one interval to the next (deltaRRi). The incidence of sustained deltaRRi changes, either decelerations or accelerations, rose with gestation (r = 0.920+/-0.057, P < 0.001) while the incidence of no detected deltaRRi changes (<+/-1 ms) diminished (r = - 0.649+/-0.364, P <0.05). Sequential decreases in fetal heart rate, increases in RRi variability and increases in changes in RRi and deltaRRi with age imply an overall maturation in autonomic cardio-regulatory control processes. Increases with gestation in measures of high frequency components of variability are compatible with enhanced parasympathetic modulation of fetal heart rate.

Animals↗
PubMed2001

Normative data for passive ankle plantarflexion--dorsiflexion flexibility.

OBJECTIVE: To describe the normal distribution parameters for measures of passive ankle plantarflexion-dorsiflexion flexibility obtained from a large sample of able-bodied young adult subjects. DESIGN: Seven variables were assessed and descriptive analyses were conducted. BACKGROUND: While assessment of plantarflexion-dorsiflexion flexibility is an important component of a clinical examination of plantarflexion contracture, there is limited normative data available that can be used as a reference for clinical decision-making. METHODS: Data were collected from 300 able-bodied male and female subjects aged between 15 and 34 years. Both ankles were measured. Load-displacement curves were collected using a manually controlled instrumented footplate. Six variables were extracted from these curves: passive torque at zero and 10 deg, passive stiffness at zero and 10 deg, and two coefficients from an equation fitted to the curve (i.e., k and b). The seventh variable, passive dorsiflexion range of motion, was quantified using a clinical procedure. RESULTS: Flexibility variables did not differ between the left and right ankles, nor between the dominant and non-dominant legs. All variables were normally distributed. These distributions can, therefore, be adequately described using their mean and standard deviation values. CONCLUSIONS: This study has substantially increased the available database on plantarflexion-dorsiflexion flexibility and forms the basis of norm-referenced clinical tests.

Adolescent↗
PubMed2004

The scale product technique as a means of enhancing the measurement of patient satisfaction.

Measurement of patient satisfaction has long been hampered by two resolvable problems: a lack of content validity in commonly used instruments, and a lack of variability in satisfaction scores when these same instruments are used. Most patient satisfaction instruments have been developed from the perspective of the provider or institution rather than that of the patient, creating a situation of questionable content validity for these measures. Additionally, most patient satisfaction measures yield data that are invariant and consistently positively biased. Both of these problems can be addressed methodologically--through tool development using a qualitative method designed to obtain the patient's perspective, and through the use of the scale product technique to decrease the effect of acquiescence, thereby increasing variability in item responses.

Bias↗
PubMedDate not supplied

Review and analysis of evaluation measures used in nutrition education intervention research.

The purpose of this review is to provide a summary of the kinds of evaluation measures used in 265 nutrition education intervention studies conducted between 1980 and 1999 and an analysis of psychometric issues arising from such a review. The data are summarized in terms of tables for interventions with each of six key population groups: preschool children, school-aged children, adults, pregnant women and breast-feeding promotion, older adults, and inservice preparation of professionals and paraprofessionals. Measures evaluating knowledge and skills or behavioral capabilities were most widely used in studies with preschool, school-aged, and inservice populations (50%-85%) and less widely used in studies with the other groups, particularly breast-feeding promotion (5%). Measures of potential psychosocial mediators or correlates of behavior such as outcome expectancies, self-efficacy, or behavioral intention were used in 90% of behaviorally focused studies with school-aged children and in about 20% of studies with adults. Dietary intake measures were used in almost all studies, primarily food recalls, records, and quantitative food frequency questionnaires. Short frequency instruments involving only foods targeted in the intervention such as fruits and vegetables are increasingly being used. Measures of specific observable behaviors are also increasingly being used. Physiologic parameters were used in about 33% of behaviorally focused interventions with school-aged children and adults, 20% with older adults, and 65% with pregnant women and/or their infants. Criterion validity of newly developed intake instruments and content validity of instruments measuring mediating variables were reported in the majority (range 50%-90%) of studies. Reliability and stability of measures of mediating variables were reported in 50% to 75% of studies, with reliability coefficients mostly about .6 to .7. Two major conclusions from this review are that evaluation measures should be appropriate to the purpose, duration, and power of the intervention and that measures should have adequate validity and reliability in relation to both the outcomes and characteristics of the target audience. Major implications are that considerable preliminary work needs to be done before any intervention study to develop and test evaluation instruments so that they are appropriate and have adequate psychometric properties, and cognitive testing of published instruments with each new target audience is essential. We will then be better able to make judgments about the effectiveness of nutrition education.

Adolescent↗
PubMed2004

Impact of coping and socioeconomic factors on quality of life in adults with asthma.

OBJECTIVE: The socioeconomic variables of income, race and employment status have been shown to influence health-related quality of life (HRQL) scores in persons with asthma. However, little is known about the impact of other psychological factors or perceptions of economic hardship on HRQL in asthma, despite the known influence these have on general activity levels and emotional perceptions. The aim of the present study was to assess the relationships between psychological and socioeconomic factors and HRQL and on subsequent changes to HRQL over 12 months. METHODOLOGY: Consecutive adult patients with moderate or severe asthma attending outpatient clinics, emergency departments or who were inpatients at two teaching hospitals, completed surveys of clinical status, psychological and socioeconomic variables, and HRQL instruments (SF-36 and Modified Marks Asthma Quality of Life Questionnaire [MAQLQ-M]), at baseline and over 12-months follow-up. RESULTS: Of 343 eligible subjects, survey responses were received from 293 at baseline and 232 at 12-months. Mean age was 42 years (SD 18), 67% were female, 42% had moderate, and 58% severe current asthma clinical status according to the National Asthma Education and Prevention Program guidelines criteria. In random-effects multiple regression models, after adjusting for age, gender, education, income and hospital, significant independent variables associated with each of total MAQLQ-M, SF-36 Physical Component Summary (PCS) and SF-36 Mental Component Summary (MCS) scores were avoidance coping, perceived recent financial difficulties and clinical asthma status. Additional independent associations were, for total MAQLQ-M, patient concerns about costs delaying them from seeking care (overall model r(2) = 0.69); for PCS, active coping (r(2) = 0.69) and for MCS, positive evaluations/satisfaction with illness (r(2) = 0.54). CONCLUSION: Psychological factors, particularly coping styles, need to be taken into account when considering HRQL scores as outcome measures in asthma. Interventions to improve the coping capabilities of individuals with moderate-to-severe asthma may be potentially important areas for improvement of asthma-related HRQL.

Adaptation, Psychological↗