Reprocessing data to form QALYs

Mapping the clinical chronic obstructive pulmonary disease questionnaire onto generic preference-based EQ-5D values

OBJECTIVES

To develop a model to predict EuroQol five-dimensional questionnaire (EQ-5D) values from clinical chronic obstructive pulmonary disease (COPD) questionnaire (CCQ) scores.

METHODS

We used data from three clinical trials (the Randomized Clinical Trial on Effectiveness of Integrated COPD Management in Primary Care [RECODE], the Assessment Of Going Home Under Early Assisted Discharge [GO-AHEAD], and the Health Status Guided COPD Care [MARCH]). Data were randomly split into an estimation sample and a validation sample. The conceptual similarity between patient-reported CCQ and preference-based EQ-5D scores was assessed using correlation and principal-component analysis. Different types of models were estimated with increasing complexity. We selected the final models on the basis of mean absolute error and root mean square error when comparing predicted and observed values from the same population (internal validity) and from different trial populations (external validity). We also developed models for different country-specific EQ-5D value sets.

RESULTS

The principal-component analysis showed that the CCQ domains functional state and mental state are associated with four dimensions of the EQ-5D. The EQ-5D dimension pain/discomfort formed a separate construct on which no CCQ item loaded. The mean observed EQ-5D values were not significantly different from the mean predicted EQ-5D values in internal validation samples but did significantly differ in external validation samples. The models underestimated EQ-5D values in milder health states and overestimated them in more severe health states. The predictive ability of the models was similar across different EQ-5D value sets.

CONCLUSIONS

The models can predict mean EQ-5D values that are similar to observed mean values in a similar population. The overestimating/underestimating of the low/high EQ-5D values, however, limits its use in Markov models. Therefore, mapping should be used cautiously.

Mapping from disease-specific measures to health-state utility values in individuals with migraine

OBJECTIVE

The objective of this study was to develop empirical algorithms that estimate health-state utility values from disease-specific quality-of-life scores in individuals with migraine.

METHODS

Data from a cross-sectional, multicountry study were used. Individuals with episodic and chronic migraine were randomly assigned to training or validation samples. Spearman's correlation coefficients between paired EuroQol five-dimensional (EQ-5D) questionnaire utility values and both Headache Impact Test (HIT-6) scores and Migraine-Specific Quality-of-Life Questionnaire version 2.1 (MSQ) domain scores (role restrictive, role preventive, and emotional function) were examined. Regression models were constructed to estimate EQ-5D questionnaire utility values from the HIT-6 score or the MSQ domain scores. Preferred algorithms were confirmed in the validation samples.

RESULTS

In episodic migraine, the preferred HIT-6 and MSQ algorithms explained 22% and 25% of the variance (R(2)) in the training samples, respectively, and had similar prediction errors (root mean square errors of 0.30). In chronic migraine, the preferred HIT-6 and MSQ algorithms explained 36% and 45% of the variance in the training samples, respectively, and had similar prediction errors (root mean square errors 0.31 and 0.29). In episodic and chronic migraine, no statistically significant differences were observed between the mean observed and the mean estimated EQ-5D questionnaire utility values for the preferred HIT-6 and MSQ algorithms in the validation samples.

CONCLUSIONS

The relationship between the EQ-5D questionnaire and the HIT-6 or the MSQ is adequate to use regression equations to estimate EQ-5D questionnaire utility values. The preferred HIT-6 and MSQ algorithms will be useful in estimating health-state utilities in migraine trials in which no preference-based measure is present.

Impact of arthroscopy of the hip for femoroacetabular impingement on quality of life at a mean follow-up of 3.2 years

The benefit of arthroscopy of the hip in the treatment of femoroacetabular impingement (FAI) in terms of quality of life (QoL) has not been reported. We prospectively collected data on 612 patients (257 women (42%) and 355 men (58%)) with a mean age at the time of surgery of 36.7 years (14 to 75) who underwent arthroscopy of the hip for FAI under the care of a single surgeon. The minimum follow-up was one year (mean 3.2 years (1 to 7)). The responses to the modified Harris hip score were translated using the Rosser Index Matrix in order to provide a QoL score. The mean QoL score increased from 0.946 (-1.486 to 0.995) to 0.974 (0.7 to 1) at one year after surgery (p < 0.001). The mean QoL score in men was significantly higher than in women, both before and one year after surgery (both p < 0.001). However, the mean change in the QoL score was not statistically different between men and women (0.02 (-0.21 to 0.27) and 0.04 (-0.16 to 0.87), respectively; p = 0.12). Linear regression analysis revealed that the significant predictors of a change in QoL score were pre-operative QoL score (p < 0.001) and gender (p = 0.04). The lower the pre-operative score, the higher the gain in QoL post-operatively (ρ = -0.66; p < 0.001). One year after surgery the QoL scores in the 612 patients had improved in 469 (76.6%), remained unchanged in 88 (14.4%) and had deteriorated in 55 (9.0%).

Is total hip arthroplasty after hip arthrodesis as good as primary arthroplasty?

BACKGROUND

Conversion of hip arthrodesis to a THA reportedly provides a reasonable solution, improving function, reducing back and knee pain, and slowing degeneration of neighboring joints associated with a hip fusion. Patients generally are satisfied with conversion despite the fact that range of mobility, muscle strength, leg-length discrepancy (LLD), persistence of limp, and need for assistive walking aids generally are worse than those for conventional primary THA.

QUESTIONS/PURPOSES

We compared THA after hip arthrodesis and primary THA to determine whether these procedures would be associated with similar functional scores, maintenance of scores with time, complications and failures, survivorship of the arthroplasty, and patient satisfaction.

PATIENTS AND METHODS

We retrospectively matched 48 patients undergoing conversion of a fused hip to a THA between January 1980 and January 2000, with 50 patients receiving a primary THA during the same period. We prospectively followed all patients between January 2000 and January 2010. The changes in function and pain after THA were compared between the two cohorts using the Harris hip score (HHS) and the Rosser Index Matrix (RIM). The Oxford hip score (OHS) and the SF-36 also were used to assess quality of life (QOL) during followup. Complications were collected and survivorship of the THA was evaluated. Patient satisfaction was assessed using the Robertsson and Dunbar questionnaire. The minimum followup was 10 years (mean, 17 years; range, 10-29 years).

RESULTS

At last followup, hip function and health-related QOL were similar for patients having conversion of hip arthrodesis to THA and for patients having a routine THA. Scores diminished overall in the two groups between 2000 and 2010, but without a difference for the HHS, RIM QOL, and OHS in the study cohort. The rate of complications, THA survival, and patient satisfaction were similar in both groups.

CONCLUSIONS

Conversion of hip arthrodesis to a THA provides substantial improvement of hip function and health-related QOL, with an acceptable rate of complications, good expectancy of survival for the arthroplasty, and high level of patient satisfaction comparable to those of primary THA.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

A review of studies mapping (or cross walking) non-preference based measures of health to generic preference-based measures

Clinical studies use a wide variety of health status measures to measure health related quality of life, many of which cannot be used in cost-effectiveness analysis using cost per quality adjusted life year (QALY). Mapping is one solution that is gaining popularity as it enables health state utility values to be predicted for use in cost per QALY analysis when no preference-based measure has been included in the study. This paper presents a systematic review of current practice in mapping between non-preference based measures and generic preference-based measures, addressing feasibility and validity, circumstances under which it should be considered and lessons for future mapping studies. This review found 30 studies reporting 119 different models. Performance of the mappings functions in terms of goodness-of-fit and prediction was variable and unable to be generalised across instruments. Where generic measures are not regarded as appropriate for a condition, mapping does not solve this problem. Most testing in the literature occurs at the individual level yet the main purpose of these functions is to predict mean values for subgroups of patients, hence more testing is required.

Quality of life in different age groups after metal-on-metal hip resurfacing arthroplasty

Hip resurfacing arthroplasty is known to improve quality of life (QoL) and allow increased activity levels in young patients. It is, however, traditionally offered to the younger age group of patients, largely those aged under 60 years. We studied 42 consecutive patients (42 hips) aged 60 years or over (mean age 64) and 41 consecutive patients (42 hips) under this age (mean age 49), all of whom had undergone a metal-on-metal hip resurfacing arthroplasty. A modified Harris hip score was translated to QoL scores using the Rosser Index Matrix immediately pre-operatively, and at six weeks, six months, one year and four years after surgery. We found a significant improvement in QoL for both groups (p <0.0001) but no difference between the two groups. The maximum improvement was reached one year after surgery. Implant survival at four years was also similar (97.6% for group I and 100% for group II). We thus conclude that in carefully selected active patients aged 60 years and over, hip resurfacing arthroplasty provides significant and equal QoL improvement as it does for those under this age with similar implant survival. For this reason, age alone should not influence a surgeon's decision to proceed with a hip resurfacing arthroplasty.

The first stage of developing preference-based measures: constructing a health-state classification using Rasch analysis

OBJECTIVE

To set out the methodological process for using Rasch analysis alongside classical psychometric methods in the development of a health-state classification that is amenable to valuation.

METHODS

The overactive bladder questionnaire is used to illustrate a five step process for deriving a reduced health-state classification from an existing non-preference-based health-related quality-of-life instrument. Step I uses factor analysis to establish instrument dimensions, step II excludes items that do not meet the initial validation process and step III uses criteria based on Rasch analysis and other psychometric testing to select the final items for the health-state classification. In step IV, item levels are examined and Rasch analysis is used to explore the possibility of reducing the number of item levels. Step V repeats steps I-IV on alternative data sets in order to validate the selection of items for the health-state classification.

RESULTS

The techniques described enable the construction of a five-dimension health-state classification, the OAB-5D, amenable to valuation tasks that will allow the derivation of preference weights.

CONCLUSIONS

The health-related quality of life of patients with conditions like overactive bladder can be valued and quality adjustment weights estimated for calculation of quality-adjusted life years.

Valuing health States for use in cost-effectiveness analysis

This article reviews the general issues in valuing health states for use in cost-effectiveness analysis and the specific issues considered by the National Institute for Health and Clinical Excellence (NICE) in its recent review of the methods of technology appraisal. The general issues are how to describe health, how to value health and who should provide the values for health. The specific issues considered by NICE included whether and what should be the reference-case instrument, what to do when there are no data using the reference-case measure, what to do when the reference-case measure is not suitable and how to judge when it is not suitable, how to review and synthesize data, and how to incorporate health-state utility values into cost-effectiveness models.

Using the effect size to model change in preference values from descriptive health status

OBJECTIVES

This pilot study describes a modelling approach to translate group-level changes in health status into changes in preference values, by using the effect size (ES) to summarize group-level improvement.

METHODS

ESs are the standardized mean difference between treatment groups in standard deviation (SD) units. Vignettes depicting varying severity in SD decrements on the SF-12 mental health summary scale, with corresponding symptom severity profiles, were valued by a convenience sample of general practitioners (n = 42) using the rating scale (RS) and time trade-off methods. Translation factors between ES differences and change in preference value were developed for five mental disorders, such that ES from published meta-analyses could be transformed into predicted changes in preference values.

RESULTS

An ES difference in health status was associated with an average 0.171-0.204 difference in preference value using the RS, and 0.104-0.158 using the time trade off.

CONCLUSIONS

This observed relationship may be particular to the specific versions of the measures employed in the present study. With further development using different raters and preference measures, this approach may expand the evidence base available for modelling preference change for economic analyses from existing data.

Estimating a preference-based single index for the Impact of Weight on Quality of Life-Lite (IWQOL-Lite) instrument from the SF-6D

OBJECTIVE

To facilitate economic evaluations of interventions for treating obesity, we estimated a preference-based single index for the Impact of Weight on Quality of Life-Lite (IWQOL-lite) instrument by mapping it onto the SF-6D preference-based index.

METHODS

A heterogeneous sample of 1972 individuals, composed of community volunteers and participants in weight loss programs, clinical trials, and gastric bypass studies, completed the IWQOL-lite, an obesity-specific measure of health-related quality of life (HRQOL), and the SF-36, a generic measure of HRQOL converted into the preference-based SF-6D. Models of the relationship between the IWQOL-lite and SF-6D of increasing complexity were estimated by regression analyses.

RESULTS

The best fitting model for predicting SF-6D index scores entered levels for each item as independent variables (R2 =0.530 in the cross-validation sample, with a mean absolute error of 0.0976). This model (1) makes fewer assumptions than those using total score, dimension scores or item scores as dependent variables and (2) provides a robust unbiased estimate of a preference-based index from IWQOL-Lite data where a preference-based measure was not used. The addition of age and body mass index (BMI) led to a slight improvement in the model.

CONCLUSIONS

It is possible to facilitate economic evaluations using results obtained from disease-specific instruments using this approach. A weakness of this approach is that there may be aspects of the condition that have not been properly reflected in the SF-6D index. It is, however, useful when a preference-based measure has not been administered and when it would be impractical to conduct a full valuation survey.

Reducing the burden of affective disorders: is evidence-based health care affordable?

BACKGROUND

Affective disorders remain the leading cause of disability burden despite the availability of efficacious treatment. A wider dissemination of evidence-based health care is likely to impact this burden, however the affordability of such a strategy at the population level is unknown. This study calculated the cost-effectiveness of evidence-based health care for depression, dysthymia and bipolar disorder in the Australian population, and determined whether it was affordable, based on current mental health-related expenditure and outcomes for these disorders.

METHODS

Cost-effectiveness was expressed in costs per years lived with disability (YLDs) averted, a population health summary measure of disability burden. Data from the Australian National Survey of Mental Health and Wellbeing, in conjunction with published randomized trials and direct cost estimates, were used to estimate the 1-year costs and YLDs averted by current health care services, and costs and outcomes for an optimal strategy of evidence-based health care.

RESULTS

Current direct mental health-related health care costs for affective disorders in Australia were 615 million dollars (1997-98 Australian dollars). This treatment averted just under 30,000 YLDs giving a cost-effectiveness ratio of 20,633 dollars per YLD. Outcome could be increased by nearly 50% at similar cost with implementation of an evidence-based package of optimal treatment, halving the cost-effectiveness ratio to 10,737 dollars per YLD.

LIMITATIONS

The method to estimate YLDs averted from the literature requires replication. The costs of implementing evidence-based health care have not been estimated.

CONCLUSIONS

Evidence-based health care for affective disorders should be encouraged on both efficacy and efficiency grounds.

Cost-utility analysis of total hip arthroplasties. Technology assessment of surgical procedures by mailed questionnaires

A retrospective study comparing 700 consecutive total hip arthroplasties, utilizing four types of implants, was performed. Questionnaires based on hip scores were sent to 593 living patients. Useful responses were received from 363 (61%) patients. Hip scores and quality-adjusted life-years were calculated. Multiple regression analysis, controlling for all possible biases, demonstrated one cementless implant as superior to all others. We believe that the use of mailed questionnaires is a simple and convenient system of follow-up, saving patients the need for outpatient clinic visits. The validity of such replies, however, has yet to be established.

Hybrid hip arthroplasty in the younger patient. Quality of life

In a hybrid hip arthroplasty, the acetabular component is uncemented. Without screw fixation, early stability depends on a press-fit. The demands placed on it by the younger patient may therefore be important. Eighty patients under the age of 70 before and after hybrid or Charnley hip arthroplasty were studied. Scores for disability and distress were used to generate quality-of-life (QOL) scores using the Rosser Index Matrix immediately before and at 1 year after surgery. All patients increased their QOL scores (P < .00006). Both groups had similar QOL scores before surgery (P = .596). At 1 year, patients with the hybrid prosthesis had slightly higher scores (P = .015). Changes in QOL scores were, however, very similar (P = .697). The use of a hybrid prosthesis does not impair early outcome.

Predicting Quality of Well-being scores from the SF-36: results from the Beaver Dam Health Outcomes Study

BACKGROUND

The SF-36 and the Quality of Well-being index (QWB) both quantify health status, yet have very different methodologic etiologies. The authors sought to develop an empirical equation allowing prediction of the QWB from the SF-36.

DATA

They used empirical observations of SF-36 profiles and QWB scores collected in interviews of 1,430 persons during the Beaver Dam Health Outcomes Study, a community-based population study of health status, and 57 persons from a renal dialysis clinic.

METHOD

The eight scales of the SF-36, their squares, and all pairwise cross-products, were used as candidate variables in stepwise and best-subsets regressions to predict QWB scores using 1,356 interviews reported in a previous paper. The resulting equation was cross-validated on the remaining 74 cases and using the renal dialysis patients.

RESULTS

A six-variable regression equation drawing on five of the SF-36 components predicted 56.9% of the observed QWB variance. The equation achieved an R2 of 49.5% on cross-validation using Beaver Dam participants and an R2 of 58.7% with the renal dialysis patients. An approximation for computing confidence intervals for predicted QWB mean scores is given.

CONCLUSION

SF-36 data may be used to predict mean QWB scores for groups of patients, and thus may be useful to modelers who are secondary users of health status profile data. The equation may also be used to provide an overall health utility summary score to represent SF-36 profile data so long as the profiles are not severely limited by floor or ceiling effects of the SF-36 scales. The results of this study provide a quantitative link between two important measures of health status.

Estimating the dollar value of health outcomes from drug-abuse interventions

OBJECTIVES

People who abuse drugs suffer from a host of medical problems that impose costs on both the abusers and society as a whole. Drug-abuse treatment and other interventions can help alleviate these medical problems, leading to health status improvements for chronic drug users and reduced social costs. The authors' dual purpose here is to (1) propose a theoretically rigorous yet easy-to-apply methodology for estimating the health-related costs of drug abuse and (2) demonstrate the methodology by estimating the potential dollar value of avoiding adverse health consequences as a result of successful drug-abuse interventions.

METHODS

The authors' proposed multiattribute quality-adjusted life year methodology for estimating the value of avoiding morbidity and mortality involves eight steps to be followed sequentially. The framework is based on developing a common unit of well-being (i.e., quality-adjusted life year) that can be applied to all types of health conditions. If all health states can be denominated in this common unit, then the process of valuation is straightforward and consistent across all types of illnesses and diseases. The methodology is relatively inexpensive to execute because the estimation procedures are not complicated technically and the data demands are modest. Also, this approach incorporates elements from several disciplines, including psychology, epidemiology, medicine, and economics. Finally, the proposed methodology is flexible enough to cover a wide range of illnesses and diseases so that consistent and comparable estimates can be generated.

RESULTS

The authors estimate the dollar value of avoiding acute hepatitis B, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS), hypertension, bacterial pneumonia, sexually transmitted diseases, and tuberculosis for a white male aged 32 years. The authors' results illustrate that estimated avoided morbidity values can vary significantly across the range of health consequences associated with drug abuse. At the upper end of the range, the value of avoiding only the morbidity associated with a single case of HIV/AIDS is approximately $157,811 for the period beginning with transmission of HIV, through late-stage HIV and AIDS, and ending just before death.

CONCLUSIONS

People who abuse drugs suffer from many medical problems in addition to their addiction. The proposed approach for estimating the dollar value of avoiding adverse health consequences provides policy analysts, evaluators, and researchers a method to calculate theoretically based benefit estimates for use in a benefit-cost analysis of drug-abuse interventions.

The use of condition specific outcome measures in economic appraisal

Despite growing concern over the use of health utility measures in economic evaluations of health care programmes, economists have been reluctant to use the wealth of knowledge contained within studies using condition specific outcome measures (CSOMs). Problems with the measurement properties of many CSOMs means that the scope for their use in economic appraisal is extremely limited. This paper examines the potential uses of CSOMs in economics, namely: to provide valid descriptive material, to provide scales for comparing the effectiveness of interventions and to 'validate' the descriptive accuracy of economic measures of benefit. It is argued that valid descriptive information is essential for economic appraisal, no matter which method of evaluation is used. Generic measures have been criticised for being too narrow and insensitive to the consequences of specific conditions. CSOMs offer a rich source of information to produce quality adjusted life years (QALYs) but two potential methods, one of mapping health states from one scale to a QALY classification (such as Rosser), and the other, developing 'exchange rates' between scales are unsatisfactory. A more rigorous approach would necessitate a major research programme of revaluing existing CSOMs using preference based methods. Another interesting avenue of research would be to use the information from CSOMs to construct health scenarios for valuation. Given the current state of development of outcome measures, it seems advisable to use CSOMs alongside economic measures in trials. Such a strategy would help demonstrate the usefulness of economic measures to clinicians and to reconcile the two measures.

Quality of Life Measurements in Eating Disorders, Angina, and Transplant Candidates: Are They Comparable?

The measurement of health-related quality of life has attracted much attention and is now a component of most big clinical trials. As we evaluate and choose between treatments and make judgements about priorities in health care, it is important that the equivalent data are available for different patient groups.

Measuring outcome in low-priority plastic surgery patients using Quality of Life indices

292 patients with a variety of "low-priority" conditions completed the Health Measurement Questionnaire self-report instrument (HMQ) on admission for surgery, and again 6 months post-operation. Comparison of the two questionnaires permitted the change in Quality of Life (QoL) to be measured. Overall, of the respondents, 73% gained benefit from surgery in terms of improvement in QoL. The largest gains were in the breast surgery group, but there were individual patients in all groups who gained substantial improvement in QoL. The results suggest that the HMQ is a useful method of measuring benefit in patients admitted for low priority plastic surgery procedures.

Measuring the impact of menopausal symptoms on quality of life

OBJECTIVE

To examine the impact of menopausal symptoms on the overall quality of life of women.

DESIGN

Data collection with a questionnaire administered by an interviewer, incorporating two different quality of life measurement techniques (time trade off and rating scale).

SETTING

Specialist menopause clinic and two general practices in Oxford.

SUBJECTS

63 women aged 45-60 years recruited opportunistically during a clinic or appointment with a general practitioner; no exclusion criteria.

RESULTS

Subjects gave very low quality of life ratings for health states with menopausal symptoms. The time trade off method of measuring preferences for these health states (on a scale from 0 to 1, where preference for full health is given as 1) yielded utility values of 0.64 for severe menopausal symptoms and 0.85 for mild symptoms. The rating scale measurement technique yielded even lower values: utilities of 0.30 and 0.65 were obtained for severe and mild symptoms respectively. Kappa scores indicated that the two methods produced results that were poorly related but not contradictory. Comparison of quality of life ratings before and after treatment with hormone replacement therapy showed significant improvements: with the rating scale measurement technique mean increases in utility values after the relief of severe and mild menopausal symptoms were 0.56 and 0.18 respectively.

CONCLUSIONS

Quality of life may be severely compromised in women with menopausal symptoms, and perceived improvements in quality of life in users of hormone replacement therapy seem to be substantial. This emphasises the need to include quality of life measurements when assessing outcomes of hormone replacement therapy. Several limitations may exist with widely applied measurement techniques, calling for the development of appropriate and well validated instruments for measuring quality of life associated with reduced health states.

Convergent validity of two measures of the quality of life

In the paper, a test of convergent validity is undertaken for two methods of quality of life assessment, one based on a shortened version of the Health Measurement Questionnaire and the other based on professional clinical judgement. The Nottingham Health Profile is used as the comparator, and the data derive from a sample of colorectal cancer patients. Criteria for convergent validity are established and both methods yield outcomes broadly consistent with such criteria.

The role of economic evaluation in setting priorities for elective surgery

Problems with waiting lists have long affected the National Health Service. The priority given by clinicians to the elective surgery conditions usually found on waiting lists is low, but the publicity surrounding the waiting lists ensures that the priority accorded elective surgery in the political arena is much higher. Waiting list initiatives have provided additional resources for the purpose of reducing the number of patients waiting for elective surgery. It is suggested that economic evaluation should form one of a package of tools used by those setting priorities within elective surgery, but that the evidence provided by previously conducted economic evaluations of elective surgery is not of sufficient quality for purchasing authorities to use as a basis for priority setting.

Epoetin: a pharmacoeconomic review of its use in chronic renal failure and its effects on quality of life

Epoetin (recombinant human erythropoietin) is an effective treatment for the anaemia of patients with chronic renal failure. It is well tolerated, and the risk of adverse effects that are caused by too rapid a correction of anaemia, for example hypertension, can be reduced in most cases by lower starting dosage regimens. Epoetin improves the quality of life of anaemic patients with end-stage renal disease (ESRD), and significant improvements in most parameters of the Kidney Disease Questionnaire, the Sickness Impact Profile and the Nottingham Health Profile have been reported by patients. However, acquisition costs of epoetin are high, thereby adding a considerable cost to ESRD therapy despite a reduction in blood transfusion requirements. Notwithstanding, although cost-effectiveness studies have indicated that epoetin is associated with higher costs of therapy, cost-benefit analysis indicates that these costs can be reduced markedly with low-dose regimens and may be completely recovered if patients regain employment.

Quality of life measures in health care. III: Resource allocation

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