Showing papers by "Maastricht University published in 1998"
TL;DR: Cognitive load theory has been designed to provide guidelines intended to assist in the presentation of information in a manner that encourages learner activities that optimize intellectual performance as discussed by the authors, which assumes a limited capacity working memory that includes partially independent subcomponents to deal with auditory/verbal material and visual/2- or 3-dimensional information as well as an effectively unlimited long-term memory, holding schemas that vary in their degree of automation.
Abstract: Cognitive load theory has been designed to provide guidelines intended to assist in the presentation of information in a manner that encourages learner activities that optimize intellectual performance. The theory assumes a limited capacity working memory that includes partially independent subcomponents to deal with auditory/verbal material and visual/2- or 3-dimensional information as well as an effectively unlimited long-term memory, holding schemas that vary in their degree of automation. These structures and functions of human cognitive architecture have been used to design a variety of novel instructional procedures based on the assumption that working memory load should be reduced and schema construction encouraged. This paper reviews the theory and the instructional designs generated by it.
4,886 citations
TL;DR: In this paper, the authors describe how technical change is locked into dominant technological regimes, and present a perspective, called strategic niche management, on how to expedite a transition into a new regime.
Abstract: The unsustainability of the present trajctories of technical change in sectors such as transport and agriculture is widely recognized. It is far from clear, however, how a transition to more sustainable modes of development may be achieved. Sustainable technologies that fulful important user requirements in terms of performance and price are most often not available on the market. Ideas of what might be more sustainable technologies exist, but the long development times, uncertainty about market demand and social gains, and the need for change at different levels in organization, technology, infastructure and the wider social and institutional context-provide a great barrier. This raises the question of how the potential of more sustainable technologies and modes of development may be exploited. In this article we describe how technical change is locked into dominant technological regimes, and present a perspective, called strategic niche management, on how to expedite a transition into a new regime. The perspective consists of the creation and/or management of nichesfor promising technologies.
2,511 citations
TL;DR: The aim of this study was to obtain consensus among experts about a set of generic core items for quality assessment of randomized clinical trials (RCTs) and the final criteria list (the Delphi list) was satisfactory to all participants.
2,150 citations
TL;DR: The basic mechanisms underlying the loss of membrane asymmetry during apoptosis are described and the novel annexin V-binding assay is discussed, an extension to the current available methods.
Abstract: Apoptosis is a programmed, physiological mode of cell death that plays an important role in tissue homeostasis. Understanding of the basic mechanisms that underlie apoptosis will point to potentially new targets of therapeutic treatment of diseases that show an imbalance between cell proliferation and cell loss. In order to conduct such research, techniques and tools to reliably identify and enumerate death by apoptosis are essential. This review focuses on a novel technique to detect apoptosis by targeting for the loss of phospholipid asymmetry of the plasma membrane. It was recently shown that loss of plasma membrane asymmetry is an early event in apoptosis, independent of the cell type, resulting in the exposure of phosphatidylserine (PS) residues at the outer plasma membrane leaflet. Annexin V was shown to interact strongly and specifically with PS and can be used to detect apoptosis by targeting for the loss of plasma membrane asymmetry. Labeled annexin V can be applied both in flow cytometry and in light microscopy in both vital and fixed material by using appropriate protocols. The annexin V method is an extension to the current available methods. This review describes the basic mechanisms underlying the loss of membrane asymmetry during apoptosis and discusses the novel annexin V-binding assay. Cytometry 31:1–9, 1998. © 1998 Wiley-Liss, Inc.
1,848 citations
TL;DR: An international group of back pain researchers considered recommendations for standardized measures in clinical outcomes research in patients with back pain and recommended a short, 6‐item questionnaire and a somewhat expanded, more precise battery of questionnaires, which would facilitate scientific advances in clinical care.
Abstract: Study Design. An international group of back pain researchers considered recommendations for standardized measures in clinical outcomes research in patients with back pain. Objectives. To promote more standardization. Summary of outcome measurement in clinical trials and other types of outcomes research, including meta-analyses, cost-effectiveness analyses, and multicenter studies. Summary of Background Data. Better standardization of outcome measurement would facilitate comparison of results among studies, and more complete reporting of relevant outcomes. Because back pain is rarely fatal or completely cured, outcome assessment is complex and involves multiple dimensions. These include symptoms, function, general well-being, work disability, and satisfaction with care. Methods. The panel considered several factors in recommending a standard battery of outcome measures. These included reliability, validity, responsiveness, and practicality of the measures. In addition, compatibility with widely used and promoted batteries such as the American Academy of Orthopaedic Surgeons Lumbar Cluster were considered to minimize the need for changes when these instruments are used. Results. First, a six-item set was proposed, which is sufficiently brief that it could be used in routine care settings for quality improvement and for research purposes. An expanded outcome set, which would provide more precise measurement for research purposes, includes measures of severity and frequency of symptoms, either the Roland or the Oswestry Disability Scale, either the SF-12 or the EuroQol measure of general health status, a question about satisfaction with symptoms, three types of disability days, and an optional single item on overall satisfaction with medical care. Conclusion. Standardized measurement of outcomes would facilitate scientific advances in clinical care. A short, 6-item questionnaire and a somewhat expanded, more precise battery of questionnaires can be recommended. Although many considerations support such recommendations, more data on responsiveness and the minimally important change in scores are needed for most of the instruments.
1,226 citations
TL;DR: In this paper, the relationship between store image, store satisfaction and store loyalty is examined and a distinction is made between true store loyalty and spurious store loyalty, manifest and latent satisfaction with the store.
Abstract: In this article the relationship between store image, store satisfaction and store loyalty is examined. A distinction is made between true store loyalty and spurious store loyalty and manifest and latent satisfaction with the store. We hypothesise that the positive relationship between manifest store satisfaction and store loyalty is stronger than the positive relationship between latent store satisfaction and store loyalty. Furthermore, we hypothesise a direct as well as an indirect effect through satisfaction of store image on store loyalty. Second, the relationship between store image and store loyalty is mediated by store satisfaction. We do not find evidence for a direct effect of store image on store loyalty.
1,204 citations
TL;DR: The objective of the study was to further unravel the prognostic significance of body weight changes in patients with COPD and to quantify the relationship between the baseline ...
Abstract: The objective of the study was to further unravel the prognostic significance of body weight changes in patients with COPD. Two survival analyses were performed: (1) a retrospective study, including 400 patients with COPD none of whom had received nutritional therapy; (2) a post hoc analysis of a prospective study, including 203 patients with COPD who had participated in a randomized placebo-controlled trial. There was no overlap between the patient groups. Baseline characteristics of all patients were collected on admission to a pulmonary rehabilitation center in stable clinical condition. In the prospective randomized placebo-controlled trial, the physiologic effects of nutritional therapy alone (n = 71) or in combination with anabolic steroid treatment (n = 67) after 8 wk was studied in patients with COPD prestratified into a depleted group and a nondepleted group. Mortality was assessed as overall mortality. The Cox proportional hazards model was used to quantify the relationship between the baseline ...
1,016 citations
TL;DR: The one-year incidence of multimorbidity was related to increasing age, public health insurance, and the presence of prevalent diseases at baseline, and statistical clustering of diseases was stronger than expected, especially among the younger subjects.
970 citations
TL;DR: Alcohol consumption is associated with a linear increase in breast cancer incidence in women over the range of consumption reported by most women, and reducing alcohol consumption is a potential means to reduce breast cancer risk.
Abstract: Objective. - To assess the risk of invasive breast cancer associated with total and beverage-specific alcohol consumption and to evaluate whether dietary and nondietary factors modify the association. Data Sources. - We included in these analyses 6 prospective studies that had at least 200 incident breast cancer cases, assessed long-term intake of food and nutrients, and used a validated diet assessment instrument. The studies were conducted in Canada, the Netherlands, Sweden, and the United States. Alcohol intake was estimated by food frequency questionnaires in each study. The studies included a total of 322 647 women evaluated for up to 11 years, including 4335 participants with a diagnosis of incident invasive breast cancer. Data Extraction. - Pooled analysis of primary data using analyses consistent with each study's original design and the random-effects model for the overall pooled analyses. Data Synthesis. - For alcohol intakes less than 60 g/d (reported by >99% of participants), risk increased linearly with increasing intake; the pooled multivariate relative risk for an increment of 10 g/d of alcohol (about 0.75-1 drink) was 1.09 (95% confidence interval [CI], 1.04-1.13; P for heterogeneity among studies, .71). The multivariate- adjusted relative risk for total alcohol intakes of 30 to less than 60 g/d (about 2-5 drinks) vs nondrinkers was 1.41 (95% CI, 1.18-1.69). Limited data suggested that alcohol intakes of at least 60 g/d were not associated with further increased risk. The specific type of alcoholic beverage did not strongly influence risk estimates. The association between alcohol intake and breast cancer was not modified by other factors. Conclusions. - Alcohol consumption is associated with a linear increase in breast cancer incidence in women over the range of consumption reported by most women. Among women who consume alcohol regularly, reducing alcohol consumption is a potential means to reduce breast cancer risk.
892 citations
TL;DR: Intervention Mapping is a framework for health education intervention development that is composed of five steps: creating a matrix of proximal program objectives, selecting theory-based intervention methods and practical strategies, designing and organizing a program, specifying adoption and implementation plans, and generating program evaluation plans.
Abstract: The practice of health education involves three major program-planning activities: needs assessment, program development, and evaluation Over the past 20 years, significant enhancements have been made to the conceptual base and practice of health education Models that outline explicit procedures and detailed conceptualization of community assessment and evaluation have been developed Other advancements include the application of theory to health education and promotion program development and implementation However, there remains a need for more explicit specification of the processes by which one uses theory and empirical findings to develop interventions This article presents the origins, purpose, and description of Intervention Mapping, a framework for health education intervention development Intervention Mapping is composed of five steps: (1) creating a matrix of proximal program objectives, (2) selecting theory-based intervention methods and practical strategies, (3) designing and organizing a program, (4) specifying adoption and implementation plans, and (5) generating program evaluation plans
880 citations
TL;DR: In this article, the authors used a methodology robust to recent criticisms of standard long-horizon event study tests to show that bidders in mergers underperform while bidder in tender o¼ers overperform in the three years after the acquisition.
TL;DR: In this article, the authors investigated how image, perceived service quality and satisfaction determine loyalty in a retail bank setting at the global construct level, as well as the level of construct dimensions.
Abstract: This article investigates how image, perceived service quality and satisfaction determine loyalty in a retail bank setting at the global construct level, as well as the level of construct dimensions. At the global level the results of a large‐scale empirical study reveal that image is indirectly related to bank loyalty via perceived quality. In turn, service quality is both directly and indirectly related to bank loyalty via satisfaction. The latter has a direct effect on bank loyalty. At the level of the dimensions underlying aforementioned constructs, it becomes clear that reliability (a quality dimension) and position in the market (an image dimension) are relatively important drivers of retail bank loyalty.
TL;DR: This article examined the effect of human and social capital upon firm dissolution with data from a population of Dutch accounting firms for the period 1880-1990 and found that human capital was captured by firm-l...
Abstract: This study examined the effect of human and social capital upon firm dissolution with data from a population of Dutch accounting firms for the period 1880–1990. Human capital was captured by firm-l...
TL;DR: A combination of the design and generation of millions to billions of different ligands, together with phage display for the isolation of binding ligands and with functional assays for identifying (and possibly selecting) bio-active ligands will provide a powerful tool for drug and target discovery well into the next decade.
TL;DR: In this paper, a theoretical framework for service loyalty consisting of three dimensions: preference loyalty, price indifference loyalty, and dissatisfaction response is developed, and the role of service quality and switching costs as antecedents to these types of service loyalty is investigated.
Abstract: In the services marketing literature it has been argued that the concept of service loyalty needs further conceptual and empirical investigation. In this paper a theoretical framework for service loyalty consisting of three dimensions: preference loyalty; price indifference loyalty; and dissatisfaction response is developed. We subsequently focus on the role of service quality and switching costs as antecedents to these types of service loyalty. The results of an empirical study of a large sample of customers from five different service industries provide support for service loyalty as a three‐dimensional construct. Moreover, we find that the influence of service quality on service loyalty varies significantly per industry and that, hence, findings from one industry cannot be generalised to other industries. Furthermore, we establish that in industries characterised by relatively low switching costs, customers will be less loyal as compared to service industries with relatively high switching costs.
University of California, San Francisco1, Washington University in St. Louis2, Mayo Clinic3, Maastricht University4, University of Washington5, University of Michigan6, Johns Hopkins University7, Emory University8, University of Gothenburg9, National Institute for Occupational Safety and Health10, University of California, Berkeley11, Harvard University12, University of Massachusetts Medical School13
TL;DR: Criteria for the classification of carpal tunnel syndrome for use in epidemiologic studies were developed by means of a consensus process and reached agreement on several conceptual issues.
Abstract: Criteria for the classification of carpal tunnel syndrome for use in epidemiologic studies were developed by means of a consensus process. Twelve medical researchers with experience in conducting epidemiologic studies of carpal tunnel syndrome participated in the process. The group reached agreement on several conceptual issues. First, there is no perfect gold standard for carpal tunnel syndrome. The combination of electrodiagnostic study findings and symptom characteristics will provide the most accurate information for classification of carpal tunnel syndrome. Second, use of only electrodiagnostic study findings is not recommended. Finally, in the absence of electrodiagnostic studies, specific combinations of symptom characteristics and physical examination findings may be useful in some settings but are likely to result in greater misclassification of disease status.
TL;DR: In this article, the authors identify theoretical antecedents and consequences of commitment in relationships in a services context and reveal that affective commitment is related to trust in the partner's honesty and benevolence, quality of the outcome of the service process, and customer satisfaction with the service being delivered.
Abstract: As with all relationships, it is commonly agreed on that partners in business must have a high degree of commitment towards their relationship. If commitment is lacking, the relationship will soon come to an end. Affective commitment, that is commitment based on attraction between partners, is to be preferred over calculative commitment. The latter form of commitment is based on constant weighing of the benefits of a relationship with a partner against the costs of that relationship. Relationships based solely on calculative commitment are also most likely not to last for an extended time. This paper identifies theoretical antecedents and consequences of commitment in relationships in a services context. The results of an empirical study reveal that affective commitment is related to trust in the partner’s honesty and benevolence, quality of the outcome of the service process, and customer satisfaction with the service being delivered. The quality of the service process has an indirect effect on affective commitment, as it is related to satisfaction. Furthermore, it is shown that affectively committed customers have a much stronger intention to stay in a relationship with a service provider than calculatively committed customers.
TL;DR: A systematic literature review was made of studies on patient priorities with regard to primary health care and aspects most often included were "informativeness", "humaneness" and "competence/accuracy".
TL;DR: In this article, the authors investigated whether the timing and incidence of a relapse of atrial fibrillation during the first month after cardioversion indicate the presence of electrical remodeling and whether this could be influenced by prevention of intracellular calcium overload during AF.
TL;DR: LV pressure-volume analysis showed that ventricular pacing reduced LV function to a similar extent after 15 minutes and 6 months of pacing, and local cardiac load regulates local cardiac mass of both myocytes and collagen.
Abstract: Background—Asynchronous electrical activation, induced by ventricular pacing, causes regional differences in workload, which is lower in early- than in late-activated regions. Because the myocardium usually adapts its mass and structure to altered workload, we investigated whether ventricular pacing leads to inhomogeneous hypertrophy and whether such adaptation, if any, affects global left ventricular (LV) pump function. Methods and Results—Eight dogs were paced at physiological heart rate for 6 months (AV sequential, AV interval 25 ms, ventricular electrode at the base of the LV free wall). Five dogs were sham operated and served as controls. Ventricular pacing increased QRS duration from 47.2±10.6 to 113±16.5 ms acutely and to 133.8±25.2 ms after 6 months. Two-dimensional echocardiographic measurements showed that LV cavity and wall volume increased significantly by 27±15% and 15±17%, respectively. The early-activated LV free wall became significantly (17±17%) thinner, whereas the late-activated septum ...
TL;DR: The model predicts that binge eating might be successfully treated with cue exposure and response prevention, and a series of predictions about clinical and non-clinical issues is derived from the model.
TL;DR: In this article, the authors define what qualitative research is about and discuss some of the difficulties involved in coming up with a clear definition of the qualitative paradigm and suggest a number of issues relating to theory and practice that warrant the existence of a new journal devoted to qualitative market research.
Abstract: Discusses a number of important issues pertaining to the domain of qualitative market research. Attempts to define what qualitative research is about and discuss some of the difficulties involved in coming up with a clear definition of the qualitative paradigm. Suggests a number of issues relating to theory and practice that warrant the existence of a new journal devoted specifically to qualitative market research. Concludes with a discussion of validity and reliability in the context of qualitative research.
TL;DR: This essay attempts to review developments with particular emphasis on the structure of lipid-binding domains of blood coagulation proteins, and the variable effect of phospholipid composition on the interaction with these proteins.
TL;DR: A contribution from UCP2 (or UCP3) to variation in metabolic rate in young Pima Indians which may contribute to overall body fat content later in life is suggested.
Abstract: The UCP2-UCP3 gene cluster maps to chromosome 11q13 in humans, and polymorphisms in these genes may contribute to obesity through effects on energy metabolism. DNA sequencing of UCP2 and UCP3 revealed three polymorphisms informative for association studies: an Ala-->Val substitution in exon 4 of UCP2, a 45 bp insertion/deletion in the 3'-untranslated region of exon 8 of UCP2 and a C-->T silent polymorphism in exon 3 of UCP3. Initially, 82 young (mean age = 30 +/- 7 years), unrelated, full-blooded, non-diabetic Pima Indians were typed for these polymorphisms by direct sequencing. The three sites were in linkage disequilibrium ( P 45 years of age were considered, heterozygotes (subjects with the highest sleeping metabolic rate) had the lowest BMI (P = 0.04). The location of the insertion/deletion polymorphism suggested a role in mRNA stability; however, it appeared to have no effect on skeletal muscle UCP2 mRNA levels in a subset of 23 randomly chosen Pima Indians. In conclusion, these results suggest a contribution from UCP2 (or UCP3) to variation in metabolic rate in young Pima Indians which may contribute to overall body fat content later in life.
TL;DR: Based on levels-of-evidence criteria, there is strong evidence to suggest that PFM exercises are effective in reducing the symptoms of SUI and there is little consistency in the studies of electrical stimulation, but when the results are combined there are strong evidence that electrostimulation is superior to sham Electrostimulation, and limited evidence that there is no difference between electrostimulations and other physical therapies.
Abstract: Objective
To assess the efficacy of physical therapies for first-line use in the treatment and prevention of stress urinary incontinence (SUI) in women, using a systematic review of randomized clinical trials (RCTs).
Materials and methods
A computer-aided and manual search for published RCTs investigating treatment and prevention of SUI using physical therapies, e.g. pelvic floor muscle (PFM) exercises, with or without other treatment modalities, was carried out. The methodological quality of the included trials was assessed using criteria based on generally accepted principles of interventional research.
Results
Twenty-four RCTs (22 treatment and two prevention) were identified; the methodological quality of the studies included was moderate and 11 RCTs were of sufficient quality to be included in further analysis. Based on levels-of-evidence criteria, there is strong evidence to suggest that PFM exercises are effective in reducing the symptoms of SUI. There is limited evidence for the efficacy of high-intensity vs a low-intensity regimen of PFM exercises. Despite significant effects of biofeedback after testing as an adjunct to PFM exercises, there is no evidence that PFM exercises with biofeedback are more effective than PFM exercises alone. There is little consistency (of stimulation types and parameters) in the studies of electrical stimulation, but when the results are combined there is strong evidence to suggest that electrostimulation is superior to sham electrostimulation, and limited evidence that there is no difference between electrostimulation and other physical therapies. In the prevention of SUI the efficacy of PFM exercises, with or without other adjuncts, is uncertain.
Conclusions
More research of high methodological quality is required to further evaluate the effects of physical therapies used to treat and prevent SUI.
TL;DR: This paper deals with some ideas which could form a basis for an IA research agenda for the next 5–10 years and focuses on the above commonalities as points of departure for exploring challenges for the future.
Abstract: There is increasing recognition and credibility for the rapidly evolving field of Integrated Assessment (IA). Within the setting of the political arena it is accepted that IA can be supportive in the long-term policy planning process, while in the scientific arena more and more scientists do realise the complementary value of IA research. One of the best indicators for this increased recognition is the establishment of the European Forum on Integrated Environmental Assessment (EFIEA) by the European Commission DGXII. In spite of this growing appreciation for IA, the methodological basis of IA is still narrow, and lags behind the high expectations from the outside world. Broadening the basis of the methodologies underlying IA should therefore be one of the top priorities of the IA community. This paper deals with some ideas which could form a basis for an IA research agenda for the next 5–10 years. One of the problems of IA is still the many definitions and interpretations that circulate (Weyant et al. [118], Rotmans and Dowlatabadi [100], Parson [85–87], Ravetz [91], Jaeger et al. [49]). Notwithstanding this diversity, these definitions have two elements in common, i.e., interdisciplinarity and decision support. These two common elements make Integrated Assessment difficult to plan and even harder to conduct. Instead of coming up with another definition of IA, we simply focus on the above commonalities as points of departure for exploring challenges for the future. Thus irrespective of whatever definition is taken, IA can be described as
TL;DR: It is concluded that addition of relatively low amounts of Caf to CES improves performance and that postexercise urinary Caf concentration remained low.
Abstract: The effect of addition of different dosages of caffeine (Caf) to a carbohydrate-electrolyte solution (CES) on metabolism, Caf excretion, and performance was examined. Subjects (n = 15) ingested 8 m...
TL;DR: In this article, the authors used the ASE model to predict the transition from pre-contemplation to transition from contemplation to quitting and found that smokers who progressed from preparation had higher self-efficacy expectations than those who did not progress.
Abstract: Cross-sectional studies integrating motivational stages with expectancy value models have suggested that contemplating smokers perceive more advantages of quitting and social support than precontemplators. Moreover, smokers preparing to quit were found to differ from precontemplators and contemplators by having higher self-efficacy expectations. Using the ASE model, the present study confirmed the findings of these cross-sectional studies. The longitudinal design of this study, however, facilitated prediction of transitions that smokers made during a 10-month follow-up. Smokers who progressed from precontemplation perceived more advantages of quitting than those who remained in precontemplation. Smokers regressed from contemplation perceived fewer advantages of quitting than those who did not regress. Finally, smokers who progressed from preparation had higher self-efficacy expectations than those who did not progress. In sum, the present study provided longitudinal support for the o-pattern, whi...
TL;DR: The results confirm that computer-generated individualized feedback can be effective in inducing recommended dietary changes and that iterative feedback can increase the longer term impact of computertailored nutrition education on fat reduction.
Abstract: A randomized trial was conducted to study the impact of individualized computer-generated nutrition information and additional effects of iterative feedback on changes in intake of fat, fruits, and vegetables. Respondents in the experimental group received computer-generated feedback letters tailored to their dietary intake, intentions, attitudes, self-efficacy expectations, and self-rated behavior. After the first feedback letter, half of the experimental group received additional iterative feedback tailored to changes in behavior and intentions. The control group received a single general nutrition information letter in a format similar to the tailored letters. Computer-tailored feedback had a significantly greater impact on fat reduction and fruit and vegetable intake than did general information. Iterative computer-tailored feedback had an additional impact on fat intake. The results confirm that computer-generated individualized feedback can be effective in inducing recommended dietary changes and that iterative feedback can increase the longer term impact of computer-tailored nutrition education on fat reduction.
TL;DR: The high fraction of basal and parabasal cells contributing to the proliferation compartment of normal human conducting-airway epithelium supports the theory that cells at or near the basement membrane are likely to be progenitor cells.
Abstract: Two roles have been suggested for basal cells on the basis of studies performed with laboratory animals: (1) anchoring of the tracheobronchial epithelium; and (2) being the epithelial stem cell. Parabasal cells located just above the basal cells have also been shown to contribute to cell renewal. However, a systematic study of the composition and proliferation of basal and parabasal cells in normal human lungs is lacking. The aims of this study were to determine in normal human conducting-airway epithelium: (1) the number of basal and parabasal cells; and (2) the contribution of basal and parabasal cells to the proliferation fraction. Samples of histologically normal tissue, free of pulmonary disease, were taken from seven lungs obtained by autopsy. Immunohistochemical staining was performed with the primary antibody MIB-1 as a proliferation marker and the antikeratin antibody 34betaE12 as a marker for basal and parabasal cells. In the largest conducting airways (diameter >= 4 mm), the percentages of basal and parabasal cells were 31% and 7%, respectively; the contribution to the proliferation compartment was 51% for basal and 33% for parabasal cells. In the smallest airways (diameter < 0.5 mm), 6% of epithelial cells were basal cells, with a 30% contribution to the proliferation compartment, whereas parabasal cells were absent. The high fraction of basal and parabasal cells contributing to the proliferation compartment of normal human conducting-airway epithelium supports the theory that cells at or near the basement membrane are likely to be progenitor cells.