Allowing for uncertainty in economic evaluations: qualitative sensitivity analysis

Sensitivity analysis allows analysts to explore the impact of uncertainty on their findings. It is an important part of any economic evaluation, and a lack of analysis is evidence of a poor quality study. Sensitivity analysis helps the analyst evaluate the reliability of conclusions for the context of the evaluation and can also facilitate consideration of the generalizability of results to other settings. The variety of one and multi-way sensitivity analyses offer simple and complementary approaches to evaluating the impact of uncertainty on the results and conclusions of economic evaluations. The paper begins with a brief discussion of the types of uncertainty that can arise in economic evaluation, and follows with suggestions of how to plan a justified sensitivity analysis. A number of specific techniques are worked through with examples, followed by a discussion of when it is best to use them. The main weakness associated with sensitivity analysis is the control that the analyst retains over three parts of the process: the choice of which variables to vary and which to treat as known or fixed; the amount of variation around the base value of the parameter that is considered clinically meaningful or policy-relevant; and the determination of what constitutes a sensitive or robust finding. It is therefore essential that the approach of the analyst is clear and justified. It is likely that the future will see further developments in the approaches and training of statistical analysis. But in the meantime, an increase in the number of evaluators undertaking a wider range of sensitivity analysis would improve the quality of evidence for, and outcomes of, decision-making.

Thromboprophylaxis following caesarean section--a comparison of the antithrombotic properties of three low molecular weight heparins--dalteparin, enoxaparin and tinzaparin

Pharmacological thromboprophylaxis is increasingly being used after caesarean section to prevent venous thromboembolism. Although a variety of low molecular weight heparins (LMWH) have been used no comparative study exists on their effects on the haemostatic system in this situation. Furthermore, their antithrombotic effect may be mediated through effects other than their inhibitory effect on activated factor X. We compared the plasma anti-factor Xa activity, plasma concentration of tissue factor pathway inhibitor (TFPI) and the reduction in plasma thrombin-antithrombin (TAT) complex concentration in 30 women randomised to receive either dalteparin 5,000 IU anti-Xa once daily (n = 10), enoxaparin 4,000 IU anti-Xa once daily (n = 10) or tinzaparin 50 IU/kg anti-Xa (average dose 3,650 anti-Xa units) once daily (n = 10) following caesarean section. Sampling occurred at 0, 1, 3, 6, 12 and 24 h relative to time of dosing. All preparations produced an increase in mean anti-Xa assay (p < 0.0001), a reduction in mean TAT (p < 0.05) and an increase in mean TFPI concentration (p <0.05). Analysis of variance (ANOVA) revealed a significant difference between the LMWHs in terms of mean anti-factor Xa activity (p < 0.005) and reduction in plasma TAT concentration (p < 0.005). Post hoc analysis indicated that the anti-Xa values of the groups receiving enoxaparin and dalteparin were significantly higher than those of the group receiving tinzaparin (p < 0.05), but not significantly different from each other. Post hoc analysis of the reduction in plasma TAT concentration showed the reduction to be significantly less in the group receiving enoxaparin compared to the dalteparin and tinzaparin groups (p < 0.05), which did not differ significantly from each other. There was no significant difference between treatment groups with regard to plasma concentration of TFPI. These findings demonstrate that LMWHs differ in their effects on haemostatic parameters including thrombin generation as assessed by TAT. The increase in TFPI may be an additional mediator of LMWH's antithrombotic effects. Although these findings demonstrate that LMWHs differ in their haemostatic effects, this does not necessarily infer a clinical difference between these agents.

Nerve pathology in the type 1 diabetic dog: effects of treatment with sulindac

The purpose of this study was to define pathological abnormalities in the peripheral nerve of a large animal model of long-duration type 1 diabetes and also to determine the effects of treatment with sulindac. Detailed morphometric studies were performed to define nerve fiber and endoneurial capillary pathology in 6 control dogs, 6 type 1 diabetic dogs treated with insulin, and 6 type 1 diabetic dogs treated with insulin and sulindac for 4 years. Myelinated fiber and regenerative cluster density showed a non-significant trend toward a reduction in diabetic compared to control animals, which was prevented by treatment with sulindac. Unmyelinated fiber density did not differ among groups. However, diabetic animals showed a non-significant trend toward an increase in axon diameter (p < 0.07), with a shift of the size frequency distribution towards larger axons, which was not prevented by treatment with sulindac. Endoneurial capillary density and luminal area showed a non-significant trend toward an increase in diabetic animals, which was prevented with sulindac treatment. Endoneurial capillary basement membrane area was significantly increased (p < 0.05) in diabetic animals, but was not prevented with sulindac treatment. We conclude that the type 1 diabetic dog demonstrates minor structural abnormalities in the nerve fibers and endoneurial capillaries of the sciatic nerve, and treatment with sulindac ameliorates some but not all of these abnormalities.

Safety of a new conjugate meningococcal C vaccine in infants

BACKGROUND

Group C conjugate meningococcal vaccines (Men C) were introduced into the UK primary immunisation schedule in November 1999. There has been extensive professional and public interest in their efficacy and safety.

AIM

To determine the occurrence of at least one uncommon adverse event in infants related to the administration of the Chiron Men C vaccine.

METHODS

A total of 2796 infants aged approximately 2 months were recruited into the study from areas in and around Sheffield and from Scotland. They were vaccinated with the Chiron Men C vaccine at 2, 3, and 4 months along with routine immunisations. Data on adverse events occurring one month after each dose were collected actively and prospectively and reviewed for possible relation to the vaccine.

RESULTS

There were no deaths. There were no serious adverse events considered definitely or probably caused by the vaccine. Four infants developed serious adverse events (hypotonia, screaming syndrome, maculopapular rash, and agitation, respectively) that were considered possibly related to the vaccine. All recovered completely. Adverse events were seen in 1804 children but were considered possibly related to the vaccine in only 49 (1.8%). On subsequent immunisation there were no recurrences of adverse events considered to be possibly related to the vaccine.

Immunity proteins: enzyme inhibitors that avoid the active site

Immunity proteins are high affinity inhibitors of colicins--SOS-induced toxins released by bacteria during times of stress. Recent work has shown that nuclease-specific immunity proteins are exosite inhibitors, binding adjacent to the enzyme active site and inhibiting colicin activity indirectly. Unusually, their binding sites comprise a near contiguous sequence that lies N-terminal to active site sequences, raising the possibility that immunity proteins bind colicins co-translationally. Exosite binding accounts for the extensive sequence diversity seen at the interfaces of colicin-immunity protein complexes, which is not only a selective advantage to colicin-producing bacteria, but also represents a powerful model system for studying specificity in protein-protein recognition.

Adverse metabolic and cardiovascular risk following treatment of acute lymphoblastic leukaemia in childhood; two case reports and a literature review

We report two patients who survived childhood acute lymphoblastic leukaemia (ALL) following treatment with chemotherapy, total body irradiation (TBI) and bone marrow transplantation (BMT). The first case presented with an acute cerebral infarction at 23 years of age and was found to have non-ketotic diabetes and gross mixed hyperlipidaemia; the second presented with non-ketotic diabetes, hypertension, proteinuria and dyslipidaemia at age 16 years. The association of glucose intolerance with other vascular risk factors in young adult survivors of BMT was recently highlighted in a follow-up study of 23 survivors of BMT [1], but none presented with such gross mixed hyperlipidaemia. The improving survival rates of childhood malignancy over the last two decades will present adult physicians with patients who have accelerated vascular risk at a young age who will require early treatment to modify it.

The use of chemotherapy to facilitate surgical resection in pleomorphic xanthoastrocytoma: experience in a single case

The use of noncytotoxic chemotherapy as an adjuvant treatment to permit resection of a pleomorphic xanthoastrocytoma (PXA) is described. A 6-year-old girl with a large right occipito-temporo-parietal lesion presented with signs and symptoms of raised intracranial pressure. An initial attempt at resection was halted because of excessive blood loss, and tumour embolisation was not feasible as no suitable vascular pedicle was identified. Two cycles of vincristine and carboplatin were given, and these decreased the vascularity of the tumour allowing subsequent complete macroscopic resection 9 weeks later. The use of chemotherapy to decrease the vascularity of the tumour by way of its antiangiogenic effects is discussed.

A double-blind, randomized comparison of the efficacy and safety of intramuscular injections of olanzapine, lorazepam, or placebo in treating acutely agitated patients diagnosed with bipolar mania

There are no rapid-acting intramuscular formulations of atypical antipsychotics available for quickly calming an agitated patient with bipolar disorder. In this study, 201 agitated patients with bipolar mania were randomly assigned to receive one to three injections of the atypical antipsychotic olanzapine (10 mg, first two injections; 5 mg, third injection), the benzodiazepine lorazepam (2 mg, first two injections; 1 mg, third injection), or placebo (placebo, first two injections; olanzapine, 10 mg, third injection) within a 24-hour period. Agitation was measured at baseline, every 30 minutes for the first 2 hours, and at 24 hours after the first injection using the Positive and Negative Syndrome Scale-Excited Component subscale and two additional agitation scales. At 2 hours after the first injection, patients treated with olanzapine showed a significantly greater reduction in scores on all agitation scales compared with patients treated with either placebo or lorazepam. At 24 hours after the first injection, olanzapine remained statistically superior to placebo in reducing agitation in patients with acute mania, whereas patients treated with lorazepam were not significantly different from those treated with placebo or olanzapine. Furthermore, no significant differences among the three treatment groups were observed in safety measures, including treatment-emergent extrapyramidal symptoms, the incidence of acute dystonia, or QTc interval changes. These findings suggest that intramuscular olanzapine is a safe and effective treatment for reducing acute agitation in patients with bipolar mania.

Pharmacokinetic/pharmacodynamic assessment of the effects of E4031, cisapride, terfenadine and terodiline on monophasic action potential duration in dog

1. Torsades de pointes (TDP) is a potentially fatal ventricular tachycardia associated with increases in QT interval and monophasic action potential duration (MAPD). TDP is a side-effect that has led to withdrawal of several drugs from the market (e.g. terfenadine and terodiline). 2. The potential of compounds to cause TDP was evaluated by monitoring their effects on MAPD in dog. Four compounds known to increase QT interval and cause TDP were investigated: terfenadine, terodiline, cisapride and E4031. On the basis that only free drug in the systemic circulation will elicit a pharmacological response target, free concentrations in plasma were selected to mimic the free drug exposures in man. Infusion regimens were designed that rapidly achieved and maintained target-free concentrations of these drugs in plasma and data on the relationship between free concentration and changes in MAPD were obtained for these compounds. 3. These data indicate that the free ED50 in plasma for terfenadine (1.9 nM), terodiline (76 nM), cisapride (11 nM) and E4031 (1.9 nM) closely correlate with the free concentration in man causing QT effects. For compounds that have shown TDP in the clinic (terfenadine, terodiline, cisapride) there is little differentiation between the dog ED50 and the efficacious free plasma concentrations in man (< 10-fold) reflecting their limited safety margins. These data underline the need to maximize the therapeutic ratio with respect to TDP in potential development candidates and the importance of using free drug concentrations in pharmacokinetic/pharmacodynamic studies.

Determination of the onset of crystallization of N1-2-(thiazolyl)sulfanilamide (sulfathiazole) by UV-Vis and calorimetry using an automated reaction platform; subsequent characterization of polymorphic forms using dispersive Raman spectroscopy

This work describes the use of UV/visible spectroscopy and calorimetry to follow the onset of crystallization of a commercially available compound, N(1)-2-(thiazolyl)sulfanilamide (sulfathiazole), during crystallization reactions performed using an automated reaction platform. Sulfathiazole has been the subject of numerous publications through which considerable confusion about the morphic form is apparent. This work does not attempt to investigate exhaustively the polymorph issue, but rather to exploit the use of the HEL auto-MATE for monitoring the onset of crystal formation. Real-time calorimetry and UV-Vis spectroscopy are compared as tools for determining the onset of crystallization. Subsequently, differential scanning calorimetry, dispersive Raman, and infrared spectroscopy analysis serve to identify the crystal forms generated by the HEL auto-MATE. A solvent-anti-solvent matrix and several bench-top crystallization experiments were performed to supplement the investigation in terms of generating the desired polymorphs.

How cuckoldry can decrease the opportunity for sexual selection: data and theory from a genetic parentage analysis of the sand goby, Pomatoschistus minutus

Alternative mating strategies are common in nature and are generally thought to increase the intensity of sexual selection. However, cuckoldry can theoretically decrease the opportunity for sexual selection, particularly in highly polygamous species. We address here the influence of sneaking (fertilization thievery) on the opportunity for sexual selection in the sand goby Pomatoschistus minutus, a marine fish species in which males build and defend nests. Our microsatellite-based analysis of the mating system in a natural sand goby population shows high rates of sneaking and multiple mating by males. Sneaker males had fertilized eggs in approximately 50% of the assayed nests, and multiple sneakers sometimes fertilized eggs from a single female. Successful males had received eggs from 2 to 6 females per nest (mean = 3.4). We developed a simple mathematical model showing that sneaking in this polygynous sand goby population almost certainly decreases the opportunity for sexual selection, an outcome that contrasts with the usual effects of cuckoldry in socially monogamous animals. These results highlight a more complex and interesting relationship between cuckoldry rates and the intensity of sexual selection than previously assumed in much of the literature on animal mating systems.

Large-scale chromatin decondensation and recondensation regulated by transcription from a natural promoter

We have examined the relationship between transcription and chromatin structure using a tandem array of the mouse mammary tumor virus (MMTV) promoter driving a ras reporter. The array was visualized as a distinctive fluorescent structure in live cells stably transformed with a green fluorescent protein (GFP)-tagged glucocorticoid receptor (GR), which localizes to the repeated MMTV elements after steroid hormone treatment. Also found at the array by immunofluorescence were two different steroid receptor coactivators (SRC1 and CBP) with acetyltransferase activity, a chromatin remodeler (BRG1), and two transcription factors (NFI and AP-2). Within 3 h after hormone addition, arrays visualized by GFP-GR or DNA fluorescent in situ hybridization (FISH) decondensed to varying degrees, in the most pronounced cases from a approximately 0.5-microm spot to form a fiber 1-10 microm long. Arrays later recondensed by 3-8 h of hormone treatment. The degree of decondensation was proportional to the amount of transcript produced by the array as detected by RNA FISH. Decondensation was blocked by two different drugs that inhibit polymerase II, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and alpha-amanitin. These observations demonstrate a role for polymerase in producing and maintaining decondensed chromatin. They also support fiber-packing models of higher order structure and suggest that transcription from a natural promoter may occur at much higher DNA-packing densities than reported previously.

Effects of haloperidol pretreatment on the smoking-induced EEG/mood activation response profile

This study examined the role of dopamine in modulating the CNS response to cigarette smoking. In a randomized, double-blind, repeated-measures design, quantitative electroencephalographic (EEG) changes and self-reports induced by the smoking of a single cigarette were assessed in 16 smokers following pretreatment with placebo and a dopamine antagonist, haloperidol (2 mg). Following placebo pretreatment, absolute (muV) and relative (%) amplitudes in slow-frequency bands (delta, theta, alpha1) were reduced and absolute and relative amplitudes in fast-frequency bands (alpha2, beta) were increased following cigarette smoking as compared to sham smoking. Haloperidol pretreatment inhibited the smoking-induced increase in absolute beta frequency. Self-ratings indicated that cigarette smoking induced increases in alertness, contentedness and calmness but not euphoria, and reduced cigarette cravings as compared to the sham smoking conditions. Smoking-induced, alpha2 increments were associated with increases in alertness and decreases in euphoria while beta increments were associated with increased calmness. Smoking-related self-ratings of mood and cigarette acceptability were not altered by haloperidol, but subjects were less content overall in the haloperidol condition as compared to placebo. Discussion of these results focuses on transmitter systems and their relationship to neuro-electric and behavioural activities associated with the smoking habit.

Effects of calorie and fluid intake on adverse events during hemodialysis

PURPOSE

To investigate the incidence of adverse events during hemodialysis treatments as a function of calories and fluid intake.

METHODS

The study period was August 3-26, 1999. Hemodialysis visits were studied. Twenty-three patients receiving hemodialysis during the 2nd shift on Tuesday, Thursday, and Saturday were studied. A total of 166 hemodialysis patient visits were studied. Data collected included: amount of fluid and food consumed, blood pressure levels, and mannitol use during each hemodialysis treatment; and any symptoms that occurred either during or after the dialysis treatment (hypotension, nausea, vomiting, diarrhea, cramping, and access problems).

RESULTS

Using regression analysis, calories and fluids were strong predictors of both hypotension (P =.003) and mannitol use (P =.000), but not of cramping or access problems. Patients were 3 times more likely to have hypotension if taking any fluids (P =.011). Patients consuming >200 calories were 2 times as likely to have hypotension (P =.058). Patients were 5 times more likely to use mannitol if taking any fluids (P =.005). Mannitol use increased significantly (P =.001) with those patients consuming >200 calories.

CONCLUSION

Patients who ate more than 200 calories and consumed more than 200 mL of fluid during hemodialysis had an increased incident of hypotensive events and increased use of mannitol.

Sural nerve fibre pathology in diabetic patients with mild neuropathy: relationship to pain, quantitative sensory testing and peripheral nerve electrophysiology

Nerve fibre pathology is poorly described in diabetic patients with mild neuropathy and has not been adequately related to clinical evaluation, quantitative sensory examination and neurophysiology. Sural nerve myelinated and unmyelinated fibre pathology was morphometrically quantified and related to the presence of pain and conventional measures of neuropathic severity in 15 diabetic patients with mild neuropathy and 14 control subjects. Diabetic patients demonstrated a significant (P < 0.01) reduction in myelinated fibre density, but no change in fibre/axonal area, or g-ratio, compared to control subjects. Unmyelinated fibre degeneration was evidenced by an increase in the percentage of unassociated Schwann cell profiles (P < 0.0001) and a reduction in axon density (P < 0.0008) in diabetic patients. This was associated with a significant reduction in unmyelinated axon diameter (P < 0.001) with a shift of the size frequency distribution to the left (P < 0.02). Neurophysiology, quantitative sensory testing and nerve fibre pathology failed to differentiate diabetic patients with painful and painless neuropathy and failed to correlate with any measure of unmyelinated fibre pathology.

The quality of care by private practitioners for sexually transmitted diseases in Uganda

One of the limited number of strategies available to reduce the spread of human immunodeficiency virus (HIV) infections in sub-Saharan Africa is the effective treatment of other, curable, sexually transmitted diseases (STDs). At present, a large proportion of people with STDs either treat themselves at home or seek treatment from private sector practitioners (PSPs) rather than use publicly funded services. A randomized controlled trial of the efficacy of a behavioural intervention with or without improved STD services is being carried out in Masaka, a rural area of south-western Uganda. The trial involves three groups, each covering six parishes. People living in one group of parishes receive information, education and communication activities (IEC) to increase public awareness regarding STDs and HIV/AIDS. The second group receives the same IEC interventions with improved treatment of STDs by both public and private service providers. The third group receives community development activities unrelated to HIV. In order to improve our understanding of how the quality of care provided by PSPs might be ameliorated, we interviewed 36 PSPs in the trial area, and made an assessment of the care they were providing. We also carried out six focus group discussions with patients to obtain their opinions on private services. PSPs in the intervention arm of the trial, who had attended meetings dealing with the syndromic management of STDs, referred to syndromes 82% of the time compared with 12% in the control arms, a mean difference of 70% (p < 0.001); stocked locally appropriate antibiotics 76% of the time compared with 52%, a mean difference of 24% (p < 0.001); and are more likely to prescribe appropriate drugs 82% of the time compared with 27%, a mean difference of 55% (p < 0.001). This small study suggests that PSPs can help improve the management of STDs.

Analysing spatially referenced public health data: a comparison of three methodological approaches

In the analysis of spatially referenced public health data, members of different disciplinary groups (geographers, epidemiologists and statisticians) tend to select different methodological approaches, usually those with which they are already familiar. This paper compares three such approaches in terms of their relative value and results. A single public health dataset, derived from a community survey, is analysed by using 'traditional' epidemiological methods, GIS and point pattern analysis. Since they adopt different 'models' for addressing the same research question, the three approaches produce some variation in the results for specific health-related variables. Taken overall, however, the results complement, rather than contradict or duplicate each other.

Cost and cost-effectiveness guidelines: which ones to use?

Given the increased awareness of the importance of cost-effectiveness in health care, there has been a growth in the number of published economic evaluations in recent years. Partly in response to concerns about deficiencies in the methodology of published studies, there has been a growth of interest in guidelines for economic evaluation. This paper reviews the various objectives of economic analyses, and then summarizes the existing groups of guidelines for cost and cost-effectiveness analyses. Finally, it compares and discusses the appropriate uses and limitations of the guidelines, with particular emphasis on those developed for applications in developing countries.

Surprising similarity of sneaking rates and genetic mating patterns in two populations of sand goby experiencing disparate sexual selection regimes

Molecular markers have proved extremely useful in resolving mating patterns within individual populations of a number of species, but little is known about how genetic mating systems might vary geographically within a species. Here we use microsatellite markers to compare patterns of sneaked fertilization and mating success in two populations of sand goby (Pomatoschistus minutus) that differ dramatically with respect to nest-site density and the documented nature and intensity of sexual selection. At the Tvärminne site in the Baltic Sea, the microsatellite genotypes of 17 nest-tending males and mean samples of more than 50 progeny per nest indicated that approximately 35% of the nests contained eggs that had been fertilized by sneaker males. Successful nest holders mated with an average of 3.0 females, and the distribution of mate numbers for these males did not differ significantly from the Poisson expectation. These genetically deduced mating-system parameters in the Tvärminne population are remarkably similar to those in sand gobies at a distant site adjoining the North Sea. Thus, pronounced differences in the ecological setting and sexual selection regimes in these two populations have not translated into evident differences in cuckoldry rates or other monitored patterns of male mating success. In this case, the ecological setting appears not to be predictive of alternative male mating strategies, a finding of relevance to sexual selection theory.