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 1,171 records · Page 65Linked to original sources
PubMed1988

Tympanometry. ASHA Working Group on Aural Acoustic-Immittance Measurements Committee on Audiologic Evaluation.

Most of the available tympanometric data have been generated with instruments that measure immittance magnitude at 226 Hz. These limited measurements are valuable in evaluating middle-ear pathologies such as effusion and tympanic-membrane perforations but are not always adequate in evaluating pathologies of the ossicular chain such as otosclerosis and ossicular discontinuity. In response to this shortcoming, manufacturers of the newest generation of immittance devices have incorporated variable frequency or click probe signals. With these new instruments, it is possible to evaluate the middle-ear transmission system over its normal range of functioning. These new instruments also are computer based. If two-component, multifrequency immittance measurements are input to the computer, it then becomes possible to analyze and plot the data in many forms. Presently, the technology has outpaced the clinical understanding of these complex measures. The intent of this tutorial was to focus on areas of tympanometry not widely discussed in previous writings. The first two sections on terminology and instrumentation encourage clinicians to know their instruments and to use standardized terminology in communicating data. Much of the remaining information focused on the new generation of multifrequency immittance systems. Examples of normal and pathological tympanograms were plotted at a number of frequencies and in a variety of formats. In the beginning, tympanometric measures will be cumbersome, but as research begins to focus on these new measurements, the best frequency range and frequency interval and the best plotting formats will be identified. In conducting these studies, the procedural (e.g., rate and direction of ear-canal pressure change and the number of successive tympanometric runs) and computational (calculation at peak or 0 daPa and calculation of ear-canal contributions) variables must be specified if the data are to be universally applicable. Once these questions are answered, tympanometric measures with computer-based instruments will be rapid and informative. Enough data do not yet exist to incorporate multiple-frequency tympanometry into screening programs. Future research will need to address the efficacy of more complex tympanometric screening procedures. It is possible that the 226-Hz screening procedure will prove most efficient in school-aged children, the majority of whom whould be identified as having middle-ear effusion by the present procedure, or in the case of ossicular-chain abnormality, would have a significant hearing loss.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Impedance Tests↗
PubMedDate not supplied

Hope and related variables in Italian cancer patients.

Hope, long considered an essential element for life, has been shown to be important among cancer patients in coping, perceived control over the illness, and psychologic adjustment to the illness. The purpose of this study was (a) to describe the level of hope in Italian cancer patients; (b) to compare the levels of hope during and after hospitalization; (c) to determine whether hope was correlated with quality of life and several symptoms; and (d) to determine whether the variables from the international literature also pertain to Italian cancer patients. A descriptive correlational design using repeated measures was chosen to study 80 Italian cancer patients during hospitalization and then at home. The following instruments were used: a Sociodemographic Questionnaire, the Hope Related Variable Questionnaire, the Nowotny Hope Scale, the Rotterdam Symptom Checklist, and the Hospital Anxiety and Depression Scale. Overall, patients were moderately hopeful and the level of hopefulness was similar in the hospital and at home. Hope was positively correlated with quality of life, self-esteem, coping, adjustment to the illness, well-being, comfort in the hospital, satisfaction with information received, relationship with, and support from family, healthcare professional, and friends. Hope was negatively correlated with anxiety, depression, and boredom during hospitalization. Time since diagnosis, illness stage, and knowing or not knowing the diagnosis and treatment were not correlated with hope. Similarities and differences with the international literature are discussed, and implications for caring for Italian cancer patients are drawn.

Adaptation, Psychological↗
PubMed2002

The variable stiffness colonoscope: assessment of efficacy by magnetic endoscope imaging.

BACKGROUND: Variable-stiffness colonoscopes combine the flexibility of pediatric instruments for negotiation of the sigmoid colon with the ability to stiffen the insertion tube to prevent or control looping after straightening. Previous studies have found wide variation in the efficacy of the stiffening mechanism. Thus, two studies were conducted to assess the potential benefit of the stiffening device and its optimal use. METHODS: In study 1, the effect of routinely stiffening the straightened variable-stiffness colonoscopes in the mid-descending colon was determined in 82 patients. Two insertions were performed (mid-descending colon to cecum) in each patient with and without application of the stiffening device (randomized). The time to negotiate the proximal colon (mid-descending to cecum), time to pass the variable-stiffness colonoscopes across the splenic flexure into the transverse colon, time to pass the right colon, and ancillary maneuvers used were recorded for each insertion. In study 2, consecutive patients, excluding any with previous colonic resection, were examined by using standard adult variable-stiffness colonoscopes. Real-time views of the procedure with magnetic endoscope imaging were recorded for all examinations, but procedures were randomized to be done either with (n = 88), or without (n = 87) the endoscopist viewing the magnetic endoscope imaging display. Whenever stiffening was applied, the anatomic location of the colonoscope tip and stiffness efficacy were recorded. RESULTS: In study 1, time taken to negotiate the proximal colon (p = 0.0041) and time to negotiate the splenic flexure (p = 0.006) were significantly shorter and ancillary maneuvers performed were fewer (p = 0.0014) with the stiffening device activated. In study 2, stiffening was used with similar frequency in patients examined with and without the magnetic endoscope imaging view, most commonly for passing the splenic flexure (71%), but also in the transverse colon (12%), right colon (9%), and sigmoid/descending colon (8%). Stiffening was significantly more effective when used in combination with magnetic endoscope imaging (69% with imager vs. 45% without imager; p = 0.0102). CONCLUSIONS: Overall, the variable-stiffness device used was effective in controlling looping 57% of the time. Activating maximum stiffness appears to be effective once the sigmoid colon has been negotiated and the colonoscope straightened with the tip in the proximal colon, reducing the number of ancillary maneuvers and shortening the insertion time through the proximal colon. Routine magnetic endoscope imaging further enhances the efficacy of the variable-stiffness colonoscopes by helping to identify the optimal time for stiffening.

Colon↗
PubMed1983

Effects of ethanol on enforced spatial variability in the 8-arm radial maze.

Previous work has indicated that ethanol is a potent stereotypy-inducing agent. At least this is the case for spontaneously emitted instrumental behavior. The present experiments were undertaken to determine if spatial variability could be generated by drugged rats when it was enforced by reward contingencies. With a reward nonreplacement rule in force, four arms of an 8-arm radial maze were baited on every trial. Rats injected with 0, 0.75, 1.5, or 2.0 g/kg ethanol were required to run to the same set of arms from trial-to-trial and session-to-session. Efficient performance depended upon their running to the correct set of arms as well as meeting a "win-shift" demand which proscribed returning to previously visited arms during a given trial. Although all groups were eventually able to run to the correct set of arms, alcohol, especially at higher doses, promoted repetition. The inability to refrain from reentering arms prevented many alcohol-injected animals from obtaining the four rewards in the allotted time. In Phase 2 of Experiment 1, the baited arms were rotated 45 degrees. Now the formerly empty arms contained pellets and rewards were withdrawn from the previously correct arms. Adjustment to this shift was rapid for 0 and 0.75 g/kg groups, but an increasingly severe perseveration was observed across the higher ethanol groups. Experiment 2 reproduced the results of Experiment 1 under different circumstances. While trained as before to run to a specific set of four arms in Phase 1, Phase 2 presented the rats with rewards in all eight arms of the maze. With higher doses of alcohol an increasing persistence in running to the original four arms was observed. Saline-injected animals, on the other hand, rapidly doubled the number of pellets taken. Taken together, and in view of earlier findings, the results suggest that alcohol interacts with previous training as well as recent choices with the result that spatial dispersion is restricted in spite of explicitly opposing reward contingencies.

Animals↗
PubMed1992

Auditing quality control procedures in a chemical pathology laboratory--a multiple regression analysis.

We undertook a retrospective analysis of the monthly test rejection rates and the monthly external quality assessment scheme performance indices for our laboratory's two automated analysers, and examined the association of these variables with measures of laboratory workload, manpower, staff training, instrument servicing, seasonal and temporal factors and changes of calibration, method and assigned internal quality control values. Using multiple linear regression and stepwise multiple linear regression, we found that test rejection rates differed significantly between instruments, and were highest on the instrument performing the widest variety and lowest volume of tests. On that instrument, rejection rates were significantly associated with the introduction of new staff and laboratory manpower levels, and also showed a highly significant trend upwards over the study period, independent of the effects of the other variables examined. External quality assessment scheme performance indices showed small trends over the study period. They were not related to the test rejection rates on either analyser but also showed a significant association with the introduction of new staff and a small but significant association with laboratory workload. We conclude that the training and introduction of new staff and decreased laboratory manpower levels may significantly increase the level of test rejection, and adherence to appropriate quality control protocols effectively maintains the quality of the laboratory's results, but may not be completely successful in filtering out the effects of some assignable causes of variation in test results. It is suggested that clinical laboratories use the statistical approach adopted here to identify factors which may be adversely affecting quality performance and running costs and to provide evidence that quality control procedures are both cost- and quality-effective.

Clinical Laboratory Techniques↗
PubMed2004

[Recent developments in kinetic perimetry].

The manual kinetic perimetry using Goldmann instrument is still widely used and remains a "gold standard" in examining patients with any kind of advanced visual field loss and impaired co-operability. Nevertheless, Goldmann instrument has several disadvantages, such as examiner dependence, response variability, lack of standardization of parameters, poor repeatability. The latest development in kinetic perimetry, which was realized at the University Eye Hospital in Tuebingen (Germany) is semi-automated kinetic perimetry (SKP), using Octopus 101 instrument (Interzeag/Haag-Streit, Koeniz-Bern, Switzerland). It is an examiner-independent, standardized and reproducible method. Additionally, obtained results can be corrected for the mean individual reaction time. This paper will briefly present characteristic, advantages and application of SKP in clinical practice.

Eye Diseases↗
PubMed2005

The role of powered instrumentation in rhinoplasty and septoplasty.

Rhinoplasty and septoplasty are commonly performed surgical procedures that have as many variables in execution as the number of surgeons that perform them. Initially, these procedures were performed using manual instrumentation. Recently, however, powered instruments have been used to perform portions of the two procedures. Powered oscillating rasps have been described for reducing dorsal bony humps during rhinoplasty, and it has been suggested that powered osteotomes may reduce tissue trauma when performing nasal osteotomies. Powered burrs have also been used for taking down dorsal bony humps and refining boney irregularities. Although septal spurs have traditionally been excised manually, powered instrumentation has proved useful in this area as well. This article reviews the indications for using powered instrumentation in rhinoplasty and septoplasty.

Humans↗
PubMed1997

Sources of systematic bias in the measurement of water by the coulometric and volumetric Karl Fischer methods.

The sources of systematic bias in the measurement of moisture by the volumetric and coulometric Karl Fischer methods were assessed. Using water-saturated octanol as a moisture standard, the measurement accuracy of five coulometric instruments was evaluated. Six possible sources of systematic bias were examined: accuracy of the moisture standard, nonadjustable instrumental bias, operator-adjustable instrumental bias, solvent composition, cell design, and sample composition. The published water content of water-saturated octanol was confirmed by the method of standard additions. The nonadjustable instrumental bias consisted of two types, one that was variable and was observed at water levels below 200 micrograms of water, and one that represented a constant percentage of the total water over the tested range from 40 to 400 micrograms of water. The adjustable instrumental parameters, if set incorrectly, may cause a small but significant negative bias (< 7%). Solvent composition as a function of both solvent type and titration vessel design can introduce a negative bias of up to 10%. Finally, the nature of the sample introduces a negative bias as demonstrated by the results obtained from titrating water in four different oil samples. Under optimum conditions, different amounts of water were measured in each oil using different Karl Fischer titration procedures and five different instruments.

Electrochemistry↗
PubMed2001

Sociodemographic predictors of self-rated health in patients with diabetes of short duration.

AIMS: To examine the impact of gender and socioeconomic factors on health-related quality of life (HRQoL) one year and eight years after diabetes diagnosis. METHODS: Two national incidence cohorts who contracted diabetes between the ages of 15 and 34 years (n=554) and matched control groups from the general population of Sweden (n=1,029) were surveyed. Data on HRQoL, diabetes treatment, marital status, education, social class, and employment were collected via a questionnaire mailed to the younger cohort (aged 16-35) one year after diagnosis and to the older cohort (aged 23-42) eight years after diagnosis. Response rates were 73% among people with diabetes and 68% among the controls. Multivariable linear regression models were used to analyse the impact of gender and socioeconomic factors on HRQoL in the diabetic and control groups. The dependent variable was the "general health perceptions" score of the SWED-QUAL instrument, which corresponds to the "global self-rated health" concept. RESULTS: A model including all the sociodemographic variables explained 6% of the variance in self-rated health one year after diabetes diagnosis and 13% of the variance eight years after diagnosis. In the control groups, the level of explanation was 2-3%. Female gender was an independent predictor of poor self-rated health in the older diabetic cohort, but not in the younger cohort. CONCLUSIONS: Gender and socioeconomic factors were more closely associated with self-rated health eight years after diabetes diagnosis than one year after diagnosis, indicating early sociodemographic stratification in the health of the diabetic populations studied.

Adolescent↗
PubMed2002

Continuous monitoring of ultrafine, fine, and coarse particles in a residence for 18 months in 1999-2000.

Continuous monitors were employed for 18 months in an occupied townhouse to measure ultrafine, fine, and coarse particles; air change rates; wind speed and direction; temperature; and relative humidity (RH). A main objective was to document short-term and long-term variation in indoor air concentrations of size-resolved particles (0.01-20 microm) caused by (1) diumal and seasonal variation of outdoor air concentrations and meteorological variables, (2) indoor sources such as cooking and using candles, and (3) activities affecting air change rates such as opening windows and using fans. A second objective was to test and compare available instruments for their suitability in providing real-time estimates of particle levels and ancillary variables. Despite different measuring principles, the instruments employed in this study agreed reasonably well for particles less than 10 microm in diameter. The three instruments measuring fine and coarse particles (aerodynamic diameter between 0.3 and 20 microm) agreed to within 30% in their overall estimates of total volume. Two of these instruments employed optical scattering, and the third used an aerodynamic acceleration principle. However, several lines of evidence indicated that the instrument employing aerodynamic acceleration overestimated concentrations for particle diameters greater than 10 microm. A fourth instrument measuring ultrafine and accumulation-mode particles (0.01-1 microm) was operated with two different inlets providing somewhat different particle size ranges. The two inlets agreed in the ultrafine region (< 0.1 microm) but diverged increasingly for larger particles (up to 0.445 microm). Indoor sources affecting ultrafine particle concentrations were observed 22% of the time, and sources affecting fine and coarse particle concentrations were observed 12 and 15% of the time, respectively. When an indoor source was operating, particle concentrations for different sizes ranged from 2 to 20 times the average concentrations when no indoor source was apparent. Indoor sources, such as cooking with natural gas, and simple physical activities, such as walking, accounted for a majority (50-90%) of the ultrafine and coarse particle concentrations, whereas outdoor sources were more important for accumulation-mode particles between 0.1 and 1 microm in diameter. Averaged for the entire year and including no periods when indoor sources were apparent, the number distribution was bimodal, with a peak at approximately 10 nm (possibly smaller), a shallow minimum at approximately 14 nm, and a second broad peak at approximately 68 nm. The volume distribution was also bimodal, with a broad peak at approximately 200 nm, a minimum at approximately 1.2 microm, and then an upward slope again through the remaining size fractions. A database was created on a 5-min averaging time basis. It contains more than 90,000 measurements by two of the instruments and approximately 30,000 by the two optical scattering instruments. About 4500 hour-long average air change rates were also calculated throughout the year using a dedicated gas chromatograph with electron capture detection (GC/ECD). At high air change rates [> 0.8 air changes per hour (hr(-1))], particle concentrations were either elevated (when no source was present) or depressed (when an indoor source was operating) by factors of up to 2 compared with low air change rates.

Air Movements↗
PubMed1996

Intrasubject variability of objective voice measures.

Recent advances in the diagnosis and treatment of voice disorders necessitate the need for accurate and reliable objective voice measurements. There are many instruments commonly used to analyze voice data. Many, if not most, of these instruments have not been adequately tested for reliability or consistency. This study evaluates the intrasubject variability of the objective voice measurements from two commonly used voice analysis instruments. The study also presents data correlating subjective mood states, room temperatures, sleep times of the subject, time since last meal, and hydration levels to the various acoustic measures. Several weak but significant correlations were obtained and are discussed. Guidelines for the appropriate use of these instruments are described.

Adult↗
PubMed1996

Perioperative blood loss: the effect of valproate.

The purpose of this investigation was to determine the effect of the use of valproate (VPA) on bleeding and requirement for replacement blood products in patients undergoing major surgical procedures. One hundred thirty-nine patients had posterior spinal fusion performed by 1 of 3 surgeons at our institution from 1987 to 1993. The clinical status of the patient, pre- and postoperative laboratory values, type and extent of instrumentation, surgeon performing the procedure, and medications (including VPA) were variables considered. The outcome measures were intra- and postoperative blood loss and number of blood products used. Intraoperative blood loss was correlated with the method of instrumentation, platelet count, and the surgeon performing the procedure. Postoperative blood loss was correlated with the diagnosis of cerebral palsy. By hierachical stepwise regression analysis, the only outcome measure correlated with VPA was the number of blood products used.

Adolescent↗
PubMed2004

Herrnstein's hyperbolic matching equation and behavioral pharmacology: review and critique.

Behavioral pharmacologists have enlisted Herrnstein's (1970) hyperbolic matching equation to understand the behavioral effects of drugs. Herrnstein's hyperbola describes the relation between absolute response rate and reinforcement rate. The equation has two fitted parameters. The parameter k represents the asymptotic response rate, and the parameter r(e) represents the reinforcement rate necessary to obtain half the asymptotic response rate. According to one interpretation of the equation, changes in k should reflect changes in response or motoric variables, and changes in r(e) should reflect changes in reinforcer or motivational variables, or changes in reinforcement from sources extraneous to the instrumental response. We review research that has applied Herrnstein's equation to distinguish the motoric from the motivational effects of drugs, and to identify additional independent variables responsible for drug effects, such as extraneous reinforcement. The validity of inferences about drug effects depends on the consistency of how k and r(e) respond to environmental manipulations: k should change only with response or motoric variables, and r(e) should change with reinforcer or motivational variables and with the rate of extraneous reinforcement. Empirical tests of these predictions, however, have produced inconsistent results. The review suggests that Herrnstein's theory has not fulfilled its promise of identifying the behavioral mechanisms of drug action. Modifications to the equation, known as bias and sensitivity, may explain some of these inconsistent results, and the modified equation may have utility in behavioral pharmacology.

Animals↗
PubMed1999

American Indian working women: correlates of subclinical depression among American Indian women.

The purpose of this study was to examine the extent to which role conflict, life satisfaction, self-esteem, instrumentality, expressiveness, age and education predicts ambulatory depression among a community based sample of urban American Indian working women. The convenience sample consisted of a total of 148 Midwestern American Indian working women, ranging in age from 18 to 65 years. Participants completed five instruments assessing gender-related traits of instrumentality and expressiveness, self-esteem, depression, life satisfaction, role conflict, and socio-demographic information. A forced entry stepwise multiple regression was conducted which included all the designated predictor variables. The significant negative Beta in Step 1 indicated that women scoring on the Masculinity (instrumentality) sub-scale were less likely to have a high depression score. The prediction of depression by the Masculinity sub-scale was no longer significant after the life satisfaction and self-esteem variables were added to the equation in Step 2. There was a significant inverse relationship for life satisfaction and self-esteem in predicting the criterion variable, depression. Thirty-two percent of the variance in the prediction of the dependent variable (depression scores) was accounted for by the six variables. In counselling urban American Indian women, supporting instrumentality, enhancing self-esteem and life satisfaction, can positively impact on ambulatory dysphoria.

Adolescent↗
PubMed1992

An evaluation of the Periotest system. Part I: Examiner reliability and repeatability of readings. Dental Implant Clinical Group (Planning Committee).

The clinical success of endosseous dental implants is related to the extent of osseointegration. Many of the presently used methods of evaluating osseointegration are highly subjective. The Periotest is claimed to offer a more objective means to assess osseointegration and supporting bone stability of implants by means of microcomputer-controlled percussion. Investigators involved in a clinical study on dental implants being conducted by the Dental Implant Clinical Research Group participated in a two-part in vitro evaluation of the Periotest system. The first part, with which this article is concerned, involved each of 35 investigators taking three readings for each of 16 models designed to simulate an implant in place in the oral cavity and to cover most of the effective measuring range of the instrument. The Periotest system generally demonstrated a high degree of reliability and repeatability, with higher variability associated with specific model samples. Further evaluation of the Periotest as a research instrument will be conducted within the clinical environment of the Dental Implant Clinical Research Group study.

Dental Implants↗
PubMed2005

Development of implantable devices for continuous ambulatory monitoring of central hemodynamic values in heart failure patients.

BACKGROUND: Care and management of patients with congestive heart failure (CHF) is a major health-care challenge. The value of acute hemodynamic data in assessing heart failure has been questioned in some studies, while more intensive hemodynamic monitoring has been reported to improve patient care in others. A series of patient studies are reported here that were conducted to identify device requirements and verify the feasibility of continuous hemodynamic monitoring in CHF patients and devices for remote transfer and use of these data. METHODS AND RESULTS: The results of four separate studies in 68 CHF patients who received systems for chronic hemodynamic monitoring between 1992 and the present are reviewed. One early study was with five patients followed for 7-16 months and another study was with nine patients followed for 4-22 months. A third study included 21 patients followed up to 39 months, and the fourth study included 32 patients implanted in 1998-99 with many of them still in follow-up. These studies support the technical feasibility of implanted devices and the external instrumentation required to transfer and manage the collected data. They also support the long-term stability and accuracy of these systems. Three additional acute studies conducted with 30 patients and chronic data from 53 of the 68 patients with the implanted systems are presented that support the feature included in the newer monitors--the ability to reliably estimate pulmonary artery diastolic pressures from the right ventricular pressure signal. CONCLUSIONS: Development of implantable technology to measure several hemodynamic variables in ambulatory CHF patients is feasible. External instrumentation needed to remotely acquire data from the implanted devices has been verified. The potential to eliminate the uncertainties associated with the use of acute, invasive hemodynamics and the ability to evaluate long-term ambulatory hemodynamic patterns is provided. These findings set the stage for determining the potential clinical value of these systems in impacting the care of chronic CHF patients.

Electrocardiography, Ambulatory↗
PubMed2005

Managing variability in the summary and comparison of gait data.

Variability in quantitative gait data arises from many potential sources, including natural temporal dynamics of neuromotor control, pathologies of the neurological or musculoskeletal systems, the effects of aging, as well as variations in the external environment, assistive devices, instrumentation or data collection methodologies. In light of this variability, unidimensional, cycle-based gait variables such as stride period should be viewed as random variables and prototypical single-cycle kinematic or kinetic curves ought to be considered as random functions of time. Within this framework, we exemplify some practical solutions to a number of commonly encountered analytical challenges in dealing with gait variability. On the topic of univariate gait variables, robust estimation is proposed as a means of coping with contaminated gait data, and the summary of non-normally distributed gait data is demonstrated by way of empirical examples. On the summary of gait curves, we discuss methods to manage undesirable phase variation and non-robust spread estimates. To overcome the limitations of conventional comparisons among curve landmarks or parameters, we propose as a viable alternative, the combination of curve registration, robust estimation, and formal statistical testing of curves as coherent units. On the basis of these discussions, we provide heuristic guidelines for the summary of gait variables and the comparison of gait curves.

Journal Article↗