Abstract: Overview The authors propose updated and revised nomenclature, definitions and classification for tooth surface lesions. Their objective is standardization, clarity and clinical utility for the dental practitioner. The article presents a schema of the pathodynamic mechanisms in the formation of tooth surface lesions—three basic physical and chemical mechanisms, their interactions and their dental manifestations. Conclusions and Clinical Implications The use of precise definitions will assist the practitioner in determining the etiology of various tooth surface lesions. Understanding the pathodynamic mechanisms and their many possible interactions, as set forth in the schema, will enable the practitioner to make an accurate differential diagnosis and to provide effective prevention and treatment. It also will assist dentists in communicating more effectively with their colleagues as well as with their patients. In addition, the schema helps identify areas in which future research is indicated.

Abstract: In this event history analysis of the 1990-1991 Schools and Staffing Survey and the 1992 Teacher Follow-up Survey, a retrospective person-year database was constructed to examine teacher attrition over the course of the teaching career. Consistent with prior research, higher teacher salaries reduced attrition, but only slightly so. Teacher attrition was no higher in socially disadvantaged schools, but poor behavioral climates did lead to greater attrition. Despite strong evidence on the effects of teacher tracking on satisfaction and efficacy, there was no evidence of higher rates of attrition among teachers who taught predominantly low-track classes. In general, school- and district-level effects were much weaker than individual-level effects.

Abstract: This volume provides a state-of-the-art treatment of research on language attrition, the non-pathological loss of a language through lack of exposure. It combines a review of past and present research with in-depth treatments of specific theoretical and methodological issues and reports on individual studies. Special prominence is given to the identification of problematic areas in attrition research, with a view to pointing out possible solutions. The book specifically addresses itself to those who wish to acquaint themselves with the research area of language attrition, providing them with both a thorough overview of the field and a basis on which to build their own research. The combination of experience and an innovative outlook present in this collection, however, make it a valuable source for those familiar with attrition as well. Especially useful to both beginners and veterans is the extensive annotated bibliography.

Abstract: The determinants of students’ propensity to drop out of university are analysed using individual records of the 1993 leaving cohort of students. The data set comprises about 100,000 individuals and allows a much more thorough analysis of student wastage than has been possible in the past. The main reasons for attrition, academic failure (‘involuntary’ attrition) and ‘voluntary’ dropout, are modelled. The results highlight, inter alia, the importance of matching and peer group effects, both of which have been found to be important determinants of student outcomes in the US but which have been subject to little empirical scrutiny for the UK.

Abstract: Attrition, or loss of participants over the course of a study, presents a significant threat to the integrity of a longitudinal research study and theory development resulting from the study. Although there has been a recent resurgence of interest in attrition, it is an underreported and understudied phenomenon despite its potential to introduce bias. Internal and external validity, reliability, and statistical validity are all impacted by a small sample and, most likely, a non-randomness in the study sample. Development of a theory of attrition will assist researchers in development of sampling strategies that will enhance the quality of their data in longitudinal designs. An ecological theoretical model of research participation is proposed and described.

Abstract: Objective. To examine the demographic, illness, and quality of care determinants of service attrition in a pediatric obesity program, and to elucidate factors that may promote families’ return to care. Design. Cross-sectional survey with semi-structured interviews. Setting. A regional children’s hospital in the United States. Study participants. Caregivers of 163 patients, consecutively enrolled in a pediatric obesity treatment program between January 1998 and September 2000, were contacted by telephone and offered participation in a survey of clinical care experiences. A total of 120 (74%) families participated. Main outcome measures. Service attrition as defined as premature discontinuation of treatment before completing phase I of a multi-phase treatment program. Results. Multivariate results indicated that service attrition was associated with both insurance status and perceived quality of care. Patients with government-subsidized insurance were more likely to defect from services than those with commercial insurance. Perceived quality of care was highly associated with attrition after controlling for demographic and health parameters. Caregiver-reported reasons for service attrition included difficulty with adequate insurance coverage (53%), the child’s desire to leave the program (50%), and the program taking too much time (32%). The most frequent suggestions to facilitate families’ return to the program were: (i) assistance with insurance coverage; (ii) following up with families; and (iii) increasing engagement with the child. Conclusions. This study found few demographic differences between patients completing the program and those defecting from services. Both families completing the program and those discontinuing prematurely rated the overall quality of the program as high. However, lower quality of care was related to increased service attrition even after controlling for the effects of demographic and health parameters. Although a considerable number of patients discontinued services, very few reported that they would not return to the program. The results provide further support for ongoing audit and examination of families’ care perceptions in preventing attrition and promoting service recovery.

Abstract: This paper provides an assessment of the nature of attrition in the HILDA Survey sample between wave 1 and wave 2. More specifically, the paper presents summary statistics on the levels of response achieved in wave 2, reports on observable differences between wave 1 respondents who did not respond in wave 2 and those that did, and examines briefly the impact of attrition on population estimates.

Abstract: This paper describes some simple simulation models of vocabulary attrition. The attrition process is modelled using a random autonomous Boolean network model, and some parallels with real attrition data are drawn. The paper argues that applying a complex systems approach to attrition can provide some important insights, which suggest that real attrition data may need to be treated with caution. It concludes that simulation methods - a technique that is not widely used in applied linguistic research - may be able to throw interesting new light on attrition, and provide a way of examining some of the assumptions that we take for granted in attrition experiments with human subjects.

Abstract: Panel data often provide an understanding of household behavior not possible with cross-sectional information alone. However, a disturbing feature of such data is that there can be substantial, nonrandom attrition and many analysts share the concern that this inhibits the ability to make accurate inferences. The author examines attrition in the KwaZulu–Natal Income Dynamics Study 1993–1998, assesses the extent of attrition bias for a specific empirical example, and proposes and implements a selection correction methodology using quality of first round interview variables as identifying instruments. The results show that attrition does lead to statistical bias in the “behavioral” coefficients in estimation of household-level expenditure functions. Since it is typically difficult to determine the bias for a particular analysis a priori, and such bias is by its nature model-specific, it behooves researchers using panel data to evaluate the effects of attrition in their analyses.

Abstract: Panel data often provide an understanding of household behavior not possible with cross-sectional information alone. However, a disturbing feature of such data is that there can be substantial, nonrandom attrition and many analysts share the concern that this inhibits the ability to make accurate inferences. The author examines attrition in the KwaZulu-Natal Income Dynamics Study 1993-1998, assesses the extent of attrition bias for a specific empirical example, and proposes and implements a selection correction methodology using quality of first round interview variables as identifying instruments. The results show that attrition does lead to statistical bias in the "behavioral" coefficients in estimation of household-level expenditure functions. Since it is typically difficult to determine the bias for a particular analysis a priori, and such bias is by its nature model-specific, it behooves researchers using panel data to evaluate the effects of attrition in their analyses.

Abstract: Attrition among medical students is a concern for the institution, the individual, and the profession. Disenrollment has an impact on the institution, in terms of academic reputation and resources expended, and the individual, in terms of self-esteem, personal finances, and opportunity costs. This study summarizes the results of an epidemiologic study of student attrition conducted at the only federal medical school in the United States--the Uniformed Services University of the Health Sciences in Bethesda, Maryland--and describes the association between demographic and selected quantitative variables for those students who graduated or remained enrolled and those who disenrolled. Both sex (female) and a decelerated curriculum were predictive of attrition in this medical student population. The records of the students who left Uniformed Services University of the Health Sciences without graduating were examined to ascertain the presence of noncognitive issues surrounding disenrollment; over one-half of the students who disenrolled left voluntarily and for nonacademic reasons.

Abstract: This volume provides a state-of-the-art treatment of research on language attrition, the non-pathological loss of a language through lack of exposure. It combines a review of past and present research with in-depth treatments of specific theoretical and methodological issues and reports on individual studies. Special prominence is given to the identification of problematic areas in attrition research, with a view to pointing out possible solutions. The book specifically addresses itself to those who wish to acquaint themselves with the research area of language attrition, providing them with both a thorough overview of the field and a basis on which to build their own research. The combination of experience and an innovative outlook present in this collection, however, make it a valuable source for those familiar with attrition as well. Especially useful to both beginners and veterans is the extensive annotated bibliography.

Abstract: Short panel data sets constructed by matching individuals across monthly files of the Current Population Survey (CPS) have been used to study a wide range of questions in labor economics. But because the CPS does not follow movers, these panels exhibit significant attrition, which may lead to bias in longitudinal estimates. The Survey of Income and Program Participation (SIPP) uses essentially the same sampling frame and design as the CPS, but makes substantial efforts to follow movers. We therefore use the SIPP to construct “data-based” rather than “model-based” corrections for bias from selective attrition. The approach is applied to two questions that have been studied with CPS data – union wage differentials and the male marriage wage premium. The evidence suggests that in many applications the advantages of using matched CPS panels to obtain longitudinal estimates are likely to far outweigh the disadvantages from attrition biases, although we should allow for the possibility that attrition bias leads the longitudinal estimates to be understated.

Abstract: This paper examines the impact of attrition among the women of the National Longitudinal Survey of Youth 1979 (NLSY79) and children in the NLSY79 Mother-Child Supplement (NLSY79-C). Attrition among the children is nonrandom with respect to mother’s marital status, grandfather’ s completed schooling, and family income. These differences that are related to the probability of attrition do not appear to impact estimates of the effects of family income or maternal employment early in the child’s life on either PPVT or BPI standard scores. However, the women who are not interviewed in any child-supplement year and the children for whom supplemental information is never collected appear to be the most disadvantaged. The omission of these children from the NLSY79-C may impact estimates of family characteristics on child outcomes, but because there are relatively few such children, the effects of their omission are likely to be small.

Abstract: OBJECTIVE: Patient dropout (attrition) can bias and threaten validity of databank-based studies. Although there are several databanks of rheumatoid arthritis (RA) in operation, this phenomenon has not been well studied. METHODS: We studied the attrition patterns of patients with RA in 11 long-running databanks where patients were followed using semiannual Health Assessment Questionnaires. Attrition rates were calculated as the proportion of living patients who were in active followup at the cutoff date. Mantel-Haenszel methods and Weibull regression were used to model the relationship between attrition and age, sex, race, education, disease duration, functional disability, and other characteristics. RESULTS: Overall, 6346 patients with RA were recruited into the study cohorts and followed for 32,823 person-years with 65,649 observations. The crude attrition rate was 3.8% per cycle. Rates were lowest in community-based databanks. Smaller size of the centers, inner-city location, and university clinic settings were associated with worse attrition. In multivariable analyses, younger age, lower levels of education, and non-Caucasian race predicted attrition. Level of disability and disease duration were not associated with attrition. Conclusion. In terms of person-years of followup and observation-points, this may be the largest study on attrition to date. While it is possible to have very high overall retention rates, certain types of databanks (smaller, inner-city-based, and university-based) are more likely to be biased due to selective retention of older, more educated Caucasian patients.

Abstract: Introduction: Although numerous articles have been published documenting parachute injuries, a search of the medical literature revealed none that detail casualty, attrition, and surgery rates for airborne operations conducted into actual combat. This study examines observed airborne casualty, attrition, and surgery rates in U.S. Army Rangers during combat operations in order to identify risk factors attributed to static-line parachute injuries and provide a comparison to estimated attrition rates. Methods: Data were recorded on standardized manual casualty cards and tracking forms while treatment was provided during two missions into Afghanistan during Operation Enduring Freedom and two missions into Iraq during Operation Iraqi Freedom, and then consolidated onto an electronic database for further analysis. Results: There were 4 airborne missions totaling 634 jumpers that resulted in 83 injuries sustained by 76 Rangers (12%). Of those, 27 Rangers (4%) were unable to continue the mission and were subsequently evacuated. There were 11 Rangers (2%) who required surgery following evacuation. The overall observed attrition rate differed from the estimated rate (p = 0.04). Although observed attrition rates did not differ from estimations in Afghanistan (p = 0.75), attrition rates in Iraq were greater than estimated rates (p = 0.02) and observed rates in Afghanistan (p = 0.05). Discussion: Many factors impact casualty, attrition, and injury patterns. Terrain and equipment load were notable associations analyzed in this study. Conclusions: Medical, logistical, and operational personnel can optimize support for airborne forces through improved estimation of casualty, attrition, and surgical rates. Risk factors associated with military parachuting can potentially provide further accuracy in estimating attrition and are recommended for integration into current models.

Abstract: OBJECTIVE To determine whether micro-computed tomography (micro-CT) could be used to reconstruct ancient dental anatomy accurately and differentiate the enamel from the dentin, as well as to verify whether micro-CT could detect tooth disorders such as attrition or caries accurately. METHODS Micro-CT imaging was performed, using a cone-beam micro-CT specimen scanner, on a 500-year-old human tooth found in a burial jar in the Cardomom Mountains in southwestern Cambodia. RESULTS The occlusal surface of the tooth showed marked attrition, with the dentin extending close to the enamel layer on the crown. In addition to this, micro-CT images depicted calculus on the buccal surface and a cervical root caries lesion present on the distal surface. The sclerotic zone of the carious lesion (located deep in the destroyed dentin) and the dentin were effectively differentiated through excellent resolution and superior tissue contrast of the volume data set. Axial slices from apical to coronal show the carious lesion extending vertically along the dentin-enamel junction with an intact outer enamel surface. CONCLUSION Micro-CT is a reproducible, nondestructive and highly accurate technique that can be successfully applied to the study of ancient teeth.

Abstract: High attrition from a selective school is an especially unexpected institutional outcome: Students and schools invest significant resources to ensure a match. This study examines the departure process underlying students’ decisions to leave college, based on a case study of attrition at a major selective urban American university. The analysis is based on in-depth interviews designed to identify the qualitative aspects of attrition as a process that leads to students’ ultimate decisions to disenroll. The results suggest that intervention may most profitably lie in the communication and interaction networks established between students and university personnel. When working successfully, such networks can enable discussion that informs students’ decisions about whether to leave or to stay. The departure process discovered at this university may possess characteristics that can inform retention policy at other institutions of higher education in both urban and nonurban settings.