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PubMed1994

The effect of stannous fluoride on dentinal hypersensitivity.

Many agents have shown varying degrees of effectiveness on pain resulting from exposed dentine. One which has shown some promising results is stannous fluoride (SnF2). The purpose of the following paper is twofold: to review and summarise the clinical literature pertaining to the relative effectiveness of solutions or gels containing SnF2 in controlling pain associated with dentinal hypersensitivity; and to statistically re-evaluate these studies in combination, in order to develop recommendations for the optimal use of SnF2 for hypersensitivity. Seven blinded clinical studies were identified and reviewed. Five of these compared 0.4 per cent SnF2 gel solution to an identical placebo. One compared a 0.4 per cent SnF2 gel solution and a 0.717 per cent F solution to an aqueous placebo. The final study compared a 0.717 per cent F solution to an aqueous placebo. Statistical power analysis and a combined meta-analysis were used to ensure adequate internal consistency and to contribute to an overall consensus of the efficacy across time. It was concluded that the 0.717 per cent F solution provides a virtually immediate and definable effect, which seems to continue for several months. This effect was present in all subjects used in the study. This solution was applied directly to the sensitive area for one minute and allowed to remain for 3-5 minutes. An additional one minute application was applied if needed. The effect of the 0.4 per cent SnF2 gel appears to be more gradual, perhaps involving a different mechanism of action. This solution requires approximately two to four weeks of continuous treatment to be effective. It was concluded that an effective strategy involving the use of stannous fluoride gel includes the application of the 0.717 per cent F solution in the office, effectively providing immediate relief. The patient would then use the 0.4 per cent SnF2 gel at home in order to achieve the long-term effect. In order to control episodic pain while the gel is developing its effect, a small amount of the 0.717 per cent F solution could be given to the patient for occasional symptomatic application.

Dentin Sensitivity↗

PubMedDate not supplied

Correction of QT values to allow for increases in heart rate in conscious Beagle dogs in toxicology assessment.

INTRODUCTION: Estimation of a direct effect of drugs on the duration of the electrocardiogram (ECG) QT interval can be confused by drug-induced increases in heart rate (HR). The objective of this assessment was to identify a correction formula that adequately corrects QT over a wide range of HRs. METHODS: Paired recordings of HR and QT interval measurements were obtained from 177 conscious Beagle dogs from both sexes in 9 toxicology studies. ECGs used for this evaluation were collected in either control vehicle-treated dogs, or from dogs prior to the first dose of a daily dosing regimen. Where more than one recording was available per dog, only one was used in the analyses. The assessments were made based on the lowest and highest pre-dose HR for each dog. Correction factors according to [Bazett, H.C. (1920). An analysis of the time relationships or time-relations of electrocardiograms. Heart 7:353-380], [Sagie, A., Larson, M.G., Goldberg, R.J., Bengtson, J.R., & Levy, D. (1992). An improved method for adjusting the QT interval for heart rate (the Framingham heart study). American Journal of Cardiology 70:797-801], [Fridericia, L.S. (1920). Die sytolendauer in elektrokardiogramm bei normalen menschen und bei herzkranken. Acta Medica Scandinavica 53:469-505.], [Todt, H., Krumpl, G., Krejcy, K. & Raberger, G. (1992). Mode of QT correction for heart rate: implications for the detection of inhomogeneous repolarization after myocardial infarction. American Heart Journal 124(3):602-609.] and [Van de Water, A., Verheyen, J., Xhonneux, R., & Reneman, R.S. (1989). An improved method to correct the QT interval of the electrocardiogram for changes in heart rate. Journal of Pharmacological Methods 22:207-217.] were applied to these QT intervals and plotted against HR. Linear regression statistical analyses using a single or multiple (i.e., baseline, sex and study) parameters model was then applied to trend lines. RESULTS: Although two correction factors ([Todt, H., Krumpl, G., Krejcy, K. & Raberger, G. (1992). Mode of QT correction for heart rate: implications for the detection of inhomogeneous repolarization after myocardial infarction. American Heart Journal 124(3):602-609.] and [Van de Water, A., Verheyen, J., Xhonneux, R., & Reneman, R.S. (1989). An improved method to correct the QT interval of the electrocardiogram for changes in heart rate. Journal of Pharmacological Methods 22:207-217.]) adequately corrected QT for changes in HR [i.e., slope of QTc versus HR not statistically significantly different from zero (p>0.05)] that of Van de Water showed a statistically superior correction. Although the method of analyses accounted for baseline, sex and study it was independently demonstrated that sex did not influence the outcome of the evaluations. Furthermore, higher HRs (i.e., maximum HRs for each dog) were better corrected than the lower HRs. In addition, statistical power analysis applied to these data showed that group sizes of 4-8 could, with 80% chance, detect a 10-5% change, respectively, in appropriately corrected QT. DISCUSSION: Overall, the data suggest that an evaluation of the most appropriate correction factor should be applied to each laboratory using their own data collected by their own method in their particular strain of dog.

Animals↗

PubMed1991

Lack of effect of a high-fat meal on the volume of distribution of theophylline in humans.

The pharmacokinetics of intravenously administered theophylline were studied in five healthy nonsmokers. Each subject received 5 mg/kg of theophylline as aminophylline after an overnight fast and again after a standard high-fat meal. Although there was wide between-day variation in the elimination rate constant in three of the five subjects, no statistically significant differences were observed in area under the time-versus-concentration curve, maximum serum theophylline concentration, elimination rate constant, or apparent volume of distribution between the two treatments. A statistical power analysis indicated that if differences in volume of distribution and maximum serum theophylline concentration occur in the general population, the mean differences are less less than 15% and 20%, respectively. This suggests that alterations in intravascular drug distribution resulting from eating a high-fat meal do not contribute importantly to previously reported effects of food on serum theophylline concentrations after oral dosing.

Adult↗

PubMed2006

Does bisphenol A induce superfeminization in Marisa cornuarietis? Part II: toxicity test results and requirements for statistical power analyses.

This study presents results of the effects of bisphenol A (BPA) on adult egg production, egg hatchability, egg development rates and juvenile growth rates in the freshwater gastropod, Marisa cornuarietis. We observed no adult mortality, substantial inter-snail variability in reproductive output, and no effects of BPA on reproduction during 12 weeks of exposure to 0, 0.1, 1.0, 16, 160 or 640 microg/L BPA. We observed no effects of BPA on egg hatchability or timing of egg hatching. Juveniles showed good growth in the control and all treatments, and there were no significant effects of BPA on this endpoint. Our results do not support previous claims of enhanced reproduction in Marisa cornuarietis in response to exposure to BPA. Statistical power analysis indicated high levels of inter-snail variability in the measured endpoints and highlighted the need for sufficient replication when testing treatment effects on reproduction in M. cornuarietis with adequate power.

Animals↗

PubMedDate not supplied

Challenges and lessons learned since implementation of the safety pharmacology guidance ICH S7A.

The International Conference on Harmonization, Topic S7A guidance (ICH S7A) on safety pharmacology for human pharmaceuticals has been in effect for 3 years in Europe, the United States and Japan. Surveys of the pharmaceutical industry, regulatory agencies and the audience attending the 4th Annual Meeting of the Safety Pharmacology Society have helped identify and address areas of controversy, as well as those challenges that have emerged since implementation of the guidance worldwide. Overall, ICH S7A has been successfully implemented. The guidance provides for "Good Laboratory Practice" compliant "safety pharmacology core battery" of studies that are generally performed prior to first administration to humans. The approach is science-driven and specifies the use of robust and sophisticated in vitro and/or in vivo assays. There are, however, some areas that require further refinement/clarification such as the specifics of study design including the selection of dose/concentration, choice of species, modeling of the temporal pharmacodynamic changes in relation to pharmacokinetic profile of parent drug and major metabolites, use of an appropriate sample size, statistical power analysis as a means of demonstrating the sensitivity of the model system, testing of human-specific metabolites and demonstrating not only the model's sensitivity, but also its specificity for predicting adverse events in humans. There was also discussion of when these studies are needed in relation to the clinical development plan. Representatives from the pharmaceutical industry and regulatory agencies see the implementation of ICH S7A as a major step forward towards identifying the risk to Phase 1 and 2 volunteers and patients. It remains to be seen, however, whether and in what ways the ICH S7A-based strategy will contribute to the modification of the integrated risk assessment during the latter stages of clinical development or once drugs have been introduced to the marketplace.

Animals↗

PubMed2001

Bladder neck circulation by Doppler ultrasonography in postmenopausal women with urinary stress incontinence.

OBJECTIVE: To investigate the effect of hormone replacement therapy (HRT) on bladder neck circulation in postmenopausal women with genuine urinary stress incontinence (USI). METHODS: A total of 227 women were enrolled in the study, including 114 postmenopausal women with USI (n = 57) or without USI (n = 57) and 113 premenopausal women with USI (n = 55) or without USI (n = 58). The bladder neck circulation was measured in 31 postmenopausal women with USI and in 12 without USI, all of whom received 0.625 mg conjugated equine estrogen plus 5 mg medroxyprogesterone acetate daily for 6 months. Bladder neck blood flow data detected by perineal color Doppler ultrasonography and weekly urinary diary data were collected before HRT and then 3 and 6 months after beginning HRT. Two-way analysis of variance and repeated measures of variance were used for statistical analysis. Power analysis was done by a two-sided test with a significance level at.05. RESULTS: The pulsatility index (PI) was significantly higher in the postmenopausal than in the premenopausal women. The postmenopausal women with USI had the highest PI level. The presence of USI did not change the PI values in the premenopausal women. After 3 months of HRT, the PI levels decreased significantly (P <.001) in the postmenopausal women with USI. The subjective improvement of USI appeared after 3 months of HRT. CONCLUSION: The blood flow around the bladder neck in women can be measured by perineal color Doppler ultrasonography. Hormone replacement therapy increases the blood flow around the bladder neck in postmenopausal women with USI. The clinical improvement of USI can be seen with HRT after 3 months.

Female↗

PubMed1996

Influence of criteria on the results of in vitro evaluation of microleakage.

OBJECTIVES: The aim of this study was to compare and explain the statistical methods employed to evaluate the in vitro sealing efficiency of adhesive restorative systems. METHODS: Two hundred and sixty sound freshly extracted human premolars were randomly divided into 13 groups. Standardized cavities were prepared, and the teeth were restored with 13 restorative systems. The teeth were thermocycled, immersed in dye, embedded in resin and sectioned. Five evaluation criteria were recorded: mean, median and mode of the data measured on each tooth, maximum dye penetration measurements on each tooth, and percentage of teeth in each group without any dye penetration. For each parameter, one-way ANOVAs and Duncan a posteriori tests were used to compare the 13 systems. RESULTS: The number of non-statistically different subgroups, pointed out by Duncan tests, was greater when the selected criterion was the maximum dye penetration (6 subgroups) or the percentage of teeth without any penetration (5 subgroups) than when the criterion was the median (3 subgroups), the mode or the mean (4 subgroups). The positioning of the 13 adhesive restorative systems established from the five criteria was different. Equivalent adhesion strategies revealing different experimental results indicate that other factors contribute to the final effectiveness of a particular system: clinical approach with respect to the formation of an elastic bonding layer, and shrinkage, physical and rheological properties of resin composite. SIGNIFICANCE: The results of these in vitro studies of dye penetration must be considered as comparisons and not as absolute conclusions. The maximum dye penetration measured on each tooth, which complies with the aim of the in vitro evaluation of sealing efficiency defined by Pashley (1990) and allows powerful statistical analysis of results, seems to be the best evaluation criterion.

Analysis of Variance↗

PubMed1997

In vitro cytotoxicity of dental adhesive systems under simulated pulpal pressure.

OBJECTIVES: Most of the devices used to evaluate the cytotoxicity of resin-based composites in vitro use a dentin barrier test. However, it is difficult to obtain the number of freshly extracted teeth, all on the same day, that is necessary for powerful statistical analysis. Tooth cryopreservation provides a way to build up a supply of teeth. This in vitro study compared cryopreserved teeth and freshly extracted teeth in an evaluation of the cytotoxicity of resin-based composites. In addition, this study also evaluated the effects of pulsatile pressure and the importance of dentin permeability on the cytotoxic response to bonding resins. METHODS: Forty freshly extracted and forty cryopreserved third molars were used. A standardized Class I cavity was prepared within the dentin. The hydraulic conductance of each tooth was recorded. The cavities were filled either with Scotchbond Multi-Purpose Plus and Z 100 (3M Dental Products) or with Optibond and Herculite (Kerr). A plexiglas device was designed to permit 24 h long contact between culture medium and the roof of the pulp chamber while a pulsatile pulpal pressure was simulated. The viability of L 929 cells cultured with a control medium and evaluated by an MTT assay was compared to that of L 929 cells cultured with medium which remained for 24 h in contact with the pulp chamber of restored teeth. A three-way ANOVA was used to compare the cytotoxicity among the different groups. A simple least-squares linear regression was used to seek a relationship between the hydraulic conductance of dentin and the cytotoxicity of composite restorative materials. RESULTS: No significant differences in cytotoxicity were found between the freshly extracted teeth and the cryopreserved teeth (p = 0.53). The cytotoxicity of the resin adhesives was statistically higher when a pulsatile pulpal pressure was simulated (p = 0.04). A significant relationship was found between the hydraulic conductance of dentin and the cytotoxicity of resin-based composites (p = 0.02). SIGNIFICANCE: Cryopreserved teeth can be used for in vitro evaluation of the cytotoxicity of resin adhesives. Pulsatile pulpal pressure simulations increased the in vitro cytotoxicity of the tested materials.

Adult↗

PubMed2002

Some design issues in a community intervention trial.

We present statistical considerations for the design of a 20-community randomized trial. The community intervention aims at multiple cancer prevention health behaviors including reducing dietary fat, increasing fruit and vegetable intake, smoking cessation, and increasing colorectal cancer screening. To better measure the overall impact of the intervention, individual endpoints as well as a global test of multiple endpoints are used. The statistical power analysis takes into account the heterogeneity between communities, the correlation between health behaviors over time, and the correlation between multiple endpoints. The study is being conducted in a relatively confined geographic area. Several measures have been taken to account for potential contamination. These include collecting information in baseline and follow-up surveys on intervention dose and conducting surveys in three similar communities in another part of the state.

Adolescent↗

PubMed1988

Focal brain ischemia in the rat: methods for reproducible neocortical infarction using tandem occlusion of the distal middle cerebral and ipsilateral common carotid arteries.

This article describes a 3-year experience with focal neocortical ischemia in three rat strains. Multiple groups of adult Wistar (n = 50), Fisher 344 (n = 31), and spontaneously hypertensive (n = 72) rats were subjected to permanent occlusion of the distal middle cerebral (MCA) and ipsilateral common carotid arteries (CCA). Twenty-four hours later the animals were killed, and frozen brain sections were stained with hematoxylin and eosin to demarcate infarcted tissue. The infarct volume for each section was quantified with an image analyzer, and the total infarct volume was calculated with an iterative program that summed all interval volumes. Neocortical infarct volume was the largest and most reproducible in the spontaneously hypertensive rats (SHR). Statistical power analysis to project the numbers of animals necessary to detect a 25 or 50% change in infarct volume with alpha = 0.05 and beta = 0.2 revealed that only the SHR model was practical in terms of requisite animals: i.e., less than 10 animals per group. Tandem occlusion of the distal MCA and ipsilateral CCA in the SHR strain provides a surgically simple method for causing large neocortical infarcts with reproducible topography and volume. The interanimal variability in infarct volume that occurs even in the SHR strain dictates that randomized, concomitant controls are necessary in each study to ensure the accurate assessment of experimental manipulations or pharmacologic therapies.

Animals↗

PubMed2005

The sensitivity of mussel-watch programmes to detect temporal trends in the bio-availability of metals. A case study of the Saronicos Gulf of Greece.

Statistical power analysis has been used to determine the sensitivity of the mussel-watch programme in Hellenic seas, with particular focus placed on the data obtained for metal content in mussels from the Saronicos Gulf during the period 1985-1997. Sample collection was carried out quarterly. Soft tissues of 60-100 similarly sized mussels (Mytilus galloprovincialis) were pooled into six composite samples and analysed by Atomic Absorption Spectroscopy (AAS). The study concludes that the resolution of monitoring programmes employed thus far is sufficiently high to detect temporal trends related to changes in contaminant levels caused either by drastic environmental control (such as those imposed on point-source pollutants) or by sudden increases in contaminant load. However, the detection of more subtle trends, which may be expected in the near future as a result of global pollution-control policies, is likely to require the adoption of much more sensitive programmes. In addition, the review of up-to-date knowledge on metal biology in mussels suggests that factors related to growth and reproduction should be taken into account to remarkably increase the resolution of mussel-watch programmes. Indicative maximum values for components of error to be complied with during routine monitoring are suggested.

Animals↗

PubMed1990

Unilateral carotid artery ligation in the Mongolian gerbil as a model for testing infarction-reducing therapies.

This study evaluates infarct size measurement as an indicator of cerebral ischaemia outcome in a placebo-controlled trial of potential cerebral protection in the unilateral carotid artery ligation in the Mongolian gerbil. Ibuprofen was used in an effort to manipulate infarct size as this agent has been shown to reduce ischaemia in myocardial infarction. Using measurements obtained through an infarct-sizing technique and a statistical power analysis of the method, the sample sizes needed to obtain significant results were projected for this model. In this case, it was not possible to demonstrate an effect of ibuprofen on infarct size although a tendency towards larger infarct size in ibuprofen-treated compared with placebo-treated gerbils was observed (36.1 +/- 10.1% versus 30.0 +/- 17.5%). The sample sizes needed to find significant changes in infarct size indicate that this model finds a practical use in studying therapies which will alter infarct size by at least 50%. For example, to detect a 30% change in infarct size, 33 successfully infarcted gerbils per group would be needed, but a 50% change would require a more tenable 13 infarcted gerbils per group. However, given the 40% infarction rate of occluded gerbils seen in this study, almost 33 gerbils per group would be required to detect a 50% change. In addition, somatosensory evoked potential was compared with neurological examination as a predictor of infarction. It would be helpful to be able to pre-screen for infarcted gerbils immediately after occlusion in order to direct infarcted gerbils into control and treated groups. Somatosensory evoked potential successfully predicted infarction with a 90% accuracy in 21 gerbils compared with neurological evaluation which was 100% accurate. But the somatosensory evoked potential prediction was made within 15 min of occlusion as opposed to the 6 h of observation during which the neurological evaluation was made.

Animals↗

PubMed1998

The relationship between parental occupation and bone cancer risk in offspring.

BACKGROUND: Bone cancers in children are serious and highly fatal conditions, yet relatively little is known about their causes or methods of prevention. METHODS: The relationship between parental occupation and bone cancer in offspring was explored in a case-control study. Cases were identified from the Ontario Cancer Registry; population-based controls were matched on sex and age. Data were collected from their parents through the use of a mailed self-administered questionnaire. RESULTS: The odds ratio estimates (OR) for bone cancer were elevated for fathers in the social sciences (OR = 2.5, 95% confidence interval [CI]: 0.7-8.4). Risk of Ewing's sarcoma was significantly high among children with fathers in social sciences (OR = 6.2, 95% CI: 1.6-24.5) and mothers in teaching (OR = 3.1, 95% CI: 1.1-8.7) or farming (OR = 7.8, 95% CI: 1.9-31.7). Osteosarcoma risk was increased for fathers in farming (OR = 2.1, 95% CI: 0.8-5.7), and mothers in managerial and administrative work (OR = 2.3, 95% CI: 0.6-8.1), and product fabricating, assembling, and repairing (OR = 2.0, 95% CI: 0.6-7.2). CONCLUSIONS: Certain methodological problems plague studies of bone cancer in children (e.g. small studies, low statistical power, analysis of multiple occupational categories, difficulty in identifying specific carcinogenic agents). These associations require further investigation, especially as elevated risks have been reported previously for agricultural occupations.

Adult↗

PubMed2006

Farm Scale Evaluations of spring-sown genetically modified herbicide-tolerant crops: a statistical assessment.

Primary results from the Farm Scale Evaluations (FSEs) of spring-sown genetically modified herbicide-tolerant crops were published in 2003. We provide a statistical assessment of the results for count data, addressing issues of sample size (n), efficiency, power, statistical significance, variability and model selection. Treatment effects were consistent between rare and abundant species. Coefficients of variation averaged 73% but varied widely. High variability in vegetation indicators was usually offset by large n and treatment effects, whilst invertebrate indicators often had smaller n and lower variability; overall, achieved power was broadly consistent across indicators. Inferences about treatment effects were robust to model misspecification, justifying the statistical model adopted. As expected, increases in n would improve detectability of effects whilst, for example, halving n would have resulted in a loss of significant results of about the same order. 40% of the 531 published analyses had greater than 80% power to detect a 1.5-fold effect; reducing n by one-third would most likely halve the number of analyses meeting this criterion. Overall, the data collected vindicated the initial statistical power analysis and the planned replication. The FSEs provide a valuable database of variability and estimates of power under various sample size scenarios to aid planning of more efficient future studies.

Agriculture↗

PubMed2006

Antimicrobial therapy using a local drug delivery system (Arestin) in the treatment of peri-implantitis. I: Microbiological outcomes.

OBJECTIVES: To assess the microbiological outcome of local administration of minocycline hydrochloride microspheres 1 mg (Arestin) in cases with peri-implantitis and with a follow-up period of 12 months. MATERIAL AND METHODS: After debridement, and local administration of chlorhexidine gel, peri-implantitis cases were treated with local administration of minocycline microspheres (Arestin). The DNA-DNA checkerboard hybridization method was used to detect bacterial presence during the first 360 days of therapy. RESULTS: At Day 10, lower bacterial loads for 6/40 individual bacteria including Actinomyces gerensceriae (P<0.1), Actinomyces israelii (P<0.01), Actinomyces naeslundi type 1 (P<0.01) and type 2 (P<0.03), Actinomyces odontolyticus (P<0.01), Porphyromonas gingivalis (P<0.01) and Treponema socranskii (P<0.01) were found. At Day 360 only the levels of Actinobacillus actinomycetemcomitans were lower than at baseline (mean difference: 1x10(5); SE difference: 0.34x10(5), 95% CI: 0.2x10(5) to 1.2x10(5); P<0.03). Six implants were lost between Days 90 and 270. The microbiota was successfully controlled in 48%, and with definitive failures (implant loss and major increase in bacterial levels) in 32% of subjects. CONCLUSIONS: At study endpoint, the impact of Arestin on A. actinomycetemcomitans was greater than the impact on other pathogens. Up to Day 180 reductions in levels of Tannerella forsythia, P. gingivalis, and Treponema denticola were also found. Failures in treatment could not be associated with the presence of specific pathogens or by the total bacterial load at baseline. Statistical power analysis suggested that a case control study would require approximately 200 subjects.

Adult↗

PubMed2003

Simulated human diving and heart rate: making the most of the diving response as a laboratory exercise.

Laboratory exercises in which students examine the human diving response are widely used in high school and college biology courses despite the experience of some instructors that the response is unreliably produced in the classroom. Our experience with this exercise demonstrates that the bradycardia associated with the diving response is a robust effect that can easily be measured by students without any sophisticated measurement technology. We discuss measures that maximize the success of the exercise by reducing individual variation, designing experiments that are minimally affected by change in the response over time, collecting data in appropriate time increments, and applying the most powerful statistical analysis. Emphasis is placed on pedagogical opportunities for using this exercise to teach general principles of physiology, experimental design, and data analysis. Data collected by students, background information for instructors, a discussion of the relevance of the diving reflex to humans, suggestions for additional experiments, and thought questions with sample answers are included.

Apnea↗

PubMed2001

Antidepressive response to sleep deprivation in unipolar depression is not associated with dopamine D3 receptor genotype.

The psychostimulant theory of antidepressive sleep deprivation (SD) proposes a contribution of dopamine D3 receptors (DRD3) in the limbic system to the antidepressant effects of SD. Neuroendocrinological studies suggest a positive correlation of clinical response to SD and cortisol secretion. We hypothesized that the clinical response to SD and amount of cortisol secretion upon SD is associated with the 1-1 genotype of the Bal1 polymorphism of DRD3 on exon 1. In this study, aiming at evaluating the feasibility of screening large patient samples, 52 inpatients (19 males/33 females) with unipolar depression and a score of 18 or more on the 21-item Hamilton Depression Rating Scale were treated with 1 night of total SD. We found that 31% of our patients responded to SD. There was no association between response to SD and the genotype of the DRD3 Bal1 polymorphism (p < 0.879). There was also no association between increase in cortisol secretion after SD and DRD3 genotypes (p < 1.000) in a subgroup of patients. Statistical power analysis ruled out a major effect of the DRD3 Bal1 polymorphism on clinical response to SD. These results suggest that the DRD3 Bal1 polymorphism is not a promising lead to be followed up in larger patient samples.

Adult↗

PubMedDate not supplied

The validity of QALYs: an experimental test of constant proportional tradeoff and utility independence.

Pliskin, Shepard, and Weinstein identified three preference conditions that ensure that quality-adjusted life years (QALYs) represent preferences over gambles over chronic health profiles. This paper presents an experimental test of the descriptive validity of two of these preference assumptions: utility independence and constant proportional tradeoff. Eighty students at the Stockholm School of Economics and 92 students at Erasmus University Rotterdam participated in the experiment. The results of the experiment support the descriptive validity of constant proportional tradeoff: both within groups and between groups constant proportional tradeoff could not be rejected. The results are less supportive of the descriptive validity of utility independence. Within-groups utility independence was rejected. Between-groups utility independence could not be rejected, but this may have been due to a lack of statistical power. Analysis of the individual responses revealed that without adjustment for imprecision of preference, 39 respondents (22.8%) satisfied constant proportional tradeoff. Twenty-three respondents (13.4%) satisfied utility independence without adjustment for imprecision of preference. However, because of the relative unfamiliarity of the respondents with both the health states to be evaluated and the methods of health-state-utility measurement, it is likely that the respondents' preferences were imprecise. Adjusted for imprecision of preference, the upper estimates of the proportions of respondents who satisfied constant proportional tradeoff and utility independence, respectively, were 90.1% (155 respondents) and 75.6% (130 respondents). Pliskin et al. further derived that if an individual's preferences satisfy both constant proportional tradeoff and utility independence, then these preferences can be represented by a more general, risk-adjusted QALY model. Without adjustment for imprecision of preference, ten respondents (5.8%) satisfied both constant proportional tradeoff and utility independence. Adjusted for imprecision of preference, the upper estimate of the proportion of respondents who satisfied both constant proportional tradeoff and utility independence was 68.6% (118 respondents). The results of this study indicate that constant proportional tradeoff holds approximately. The evidence is much weaker for utility independence, however. This has important implications for the use of QALY-type measures in medical decision making.

Activities of Daily Living↗