Production of IL-1 alpha and IL-1 beta by human skin equivalents parasitized by Sarcoptes scabiei

Human skin equivalents (HSEs) were used as a model to investigate interleukin (IL)-1 alpha and IL-1 beta secretions by keratinocytes stimulated by Sarcoptes scabiei (SS). SS mites burrowed into the stratum corneum when placed on the surface of cultured HSEs. Mites lived for 14 days. Mites and mite products induced cells in the HSEs to secrete IL-1 alpha and IL-1 beta within 16 hr. Scabies mites induced production of greater amounts of IL-1 alpha than IL-1 beta. Hepatocyte growth factor in the culture medium at 3 and 30 ng/ml upregulated the secretions of both IL-1 alpha and IL-1 beta by mite-infested skin equivalents, whereas 10 ng/ml of IL-6 upregulated production of only IL-1 beta. Therefore, these cytokines were important immunomodulating factors influencing keratinocyte secretion of IL-1 alpha and IL-1 beta in vitro. The results of this study provide the first evidence that keratinocytes (possibly fibroblasts) in the skin produce these cytokines in response to scabies mites or other ectoparasitic arthropods. Because IL-1 alpha and IL-1 beta are potent inducers of inflammation and keratinocytes are among the first effector cells to encounter scabies mites and their products, these cells may be key initiators of the inflammatory/immune reaction to scabies.     

The influence of induced abortion on Taiwanese fertility

Data on the outcomes of more than 15,000 pregnancies originating between May 1966 and February 1969 were analyzed. The accuracy of the data was evaluated, rates of induced abortion and stillbirth were reported, and the demographic effect of induced abortion was estimated. The demographic effect was defined as the percentage increase in fertility that would have occurred in the absence of induced abortion, assuming no compensating change in alternative fertility control practices. Our principal findings were as follows: 1. We were unable to determine the completeness with which induced abortion was reported in the Registration Study. During the three years covered by the study, rates of induced abortion increased by 54 percent, reflecting a trend in the incidence or in the reporting of events or in both. We concluded that, in any case, the data for the final year of the study, 1968, were more complete than for the earlier two years. 2. Age-specific rates of induced abortion for 1968 displayed a strong urban-rural gradient, being much higher in the city areas than in the rural areas. Within each urban--rural stratum, the rates increases monotonically with age and reached maximum values in the age group 40 and older (553, 436, and 374 per 1,000 pregnancies for city, urban, and rural areas, respectively). 3. Estimates of the demographic effect indicated that, in the absence of induced abortion, the TFR for all Taiwan would have been 12 percent higher in 1968. Under the same assumption, it was estimated that the TFR would have been higher by 16 percent in city areas, 11 percent in urban areas, and 9 percent in rural areas. This urbanization gradient implies that induced abortion contributed to urban-rural fertility differentials. We estimated that about one-third of those differentials were due to induced abortion. 4. Estimates of the demographic effect were also made after adjusting the rates of induced abortion for an assumed level of underreporting of 50 percent. The adjusted estimate of the demographic effect for all Taiwan in 1968 was 19 percent.     

Cardiac transplantation in perspective for the future. Survival, complications, rehabilitation, and cost

Two hundred twenty-seven cardiac transplant procedures have been performed in 206 patients from January, 1968, to April, 1981. Postoperative survival rates, calculated by the actuarial method for program years 1968 to 1973 (66 patients), are 44%, 33%, 27%, 21%, and 18% at 1, 2, 3, 4, and 5 years after transplantation, respectively. Postoperative survival rates for program years 1974 to 1981 (140 patients) are 63%, 55%, 51, 44%, and 39% at 1, 2, 3, 4, and 5 years after transplantation, respectively. This increase results primarily from improvement in survival achieved in the first 3 postoperative months (59% +/- 7%, 1968 to 1973, versus 80% +/- 40%, 1974 to 1980), reflecting improved patient management. Infection remains the primary cause of death following transplantation (76/131 patients, 58%), followed by acute rejection (24/181, 18.3%), graft arteriosclerosis (14/131, 10.7%), and malignancy (6/131, 4.6%). The development of graft arteriosclerosis has been examined in 85 one-year survivors studied by annual coronary arteriograms. Coronary lesions of varying severity have developed in 21 patients. HLA-A2 incompatibility was associated with a higher incidence of graft arteriosclerosis than was apparent for all other A locus incompatibilities (p less than 0.0003). Lymphoma has been shown to be associated with younger recipient age, a primary disease diagnosis of idiopathic cardiomyopathy, and retransplantation. One hundred six patients have survived at least 1 year after transplantation; 97% were in NYHA Class 1 at that time interval and 82% returned to employment or activity of choice. The longest survival time is new 11 years, 3 months. Cardiac transplantation can be considered "reasonable and therapeutic treatment to extend life" in selected individuals.     

General practitioner attitudes toward mandatory reporting of doctor-patient sexual abuse

AIM: To explore general practitioner attitudes toward mandatory reporting of doctor-patient sexual abuse. METHODS: Anonymous questionnaire mailed to a randomised sample of 217 New Zealand general practitioners. Attitudes toward mandatory reporting of doctor-patient sexual contact, seductive or sexually demeaning behaviour were appraised including an indication of whom the perceived appropriate reporting body should be. RESULTS: Forty-seven per cent of respondents supported the notion of mandatory reporting for doctor-patient sexual contact, 42% for sexually demeaning behaviour and 35% for seductive verbal behaviour. These respondents indicated that the most appropriate body to report to was a Doctor's Health Advisory Service. CONCLUSION: There was a lack of strong consensus on mandatory reporting of doctor-patient sexual abuse.     

Contrast sensitivity in patients with silicone intraocular lenses

Meningococcal clone ET-15/37, which appeared as a new one in the Czech Republic in 1993, caused an emergency epidemiological and clinical situation in invasive meningococcal disease, characterized by a high fatality rate (20%) compared to the "normal" fatality rate due to "non ET-15/37" strains. Morbidity rate increased since the first year of the new clone occurrence and reached the peak in 1995. This clone has spread all over the country and investigation of the epidemiological markers of Neisseria meningitidis allowed to quickly recognize the emergency situation and subsequently to provide a targeted vaccination with A + C polysaccharide meningococcal vaccine which prevented the spread of the disease caused by Neisseria meningitidis C. The most frequent phenotype of ET-15/37 clone was C:2a:P1.2(P1.5) and its percentage achieved 80% of group C Neisseria meningitidis strains tested. This antigenic shift of Neisseria meningitidis was associated with the age shift in invasive meningococcal disease morbidity: teenagers started to be the most affected age group and later age group of 1-4 olds followed with high morbidity rates. In 1995 B variant of ET-15/37 clone, B:2a:P1.2(P1.5), appeared, causing a high fatality rate, too. Some data are indicative of a possible decrease in the invasive meningococcal disease incidence in the Czech Republic; nevertheless, the active surveillance and detailed investigation of meningococci have to be continued. After four years following the vaccination and chemoprophylaxis strategy recommended in the Guidelines, set up by the National Reference Laboratory for Meningococcal Infections in 1993, it is possible to conclude, that there have been practically no secondary cases of invasive meningococcal disease in the Czech Republic.     

Primary retroperitoneal germ cell tumours: excision via a thoracoabdominal extraperitoneal approach

BACKGROUND: Primary retroperitoneal germ cell tumours usually present as a large abdominal mass in young men. The testes are normal on examination and ultrasonography but there are usually raised serum levels of human chorionic gonadotrophin and/or alpha-fetoprotein. METHODS: Fourteen men (median age 33 years) with primary retroperitoneal germ cell tumours were treated by chemotherapy followed by surgical resection of the primary tumour and metastases via a thoracoabdominal extraperitoneal approach. RESULTS: There was minimal morbidity. The survival rate was 13 of 14 and the disease-free survival rate was 11 of 14 after a median follow-up of 15 months. CONCLUSION: The thoracoabdominal extraperitoneal approach for the removal of retroperitoneal germ cell tumours and their metastases after chemotherapy improves tumour clearance, morbidity and recovery time compared with the transperitoneal anterior approach.     

Long term results of treatment of carcinoma of cervix

In this survey of 602 patients treated for carcinoma of the uterine cervix during the period 1944--1968 (with a 100 per cent follow-up) survival rates at 5, 10, 15 and 20 years after radiotherapy were 41, 28, 18 and 11 per cent. The crude five-year cure rate of over 70 per cent for Stage I and 58 per cent for Stage II cases and an overall five-year survival rate of 42 per cent for all stages compares favourably with results published from other institutions in the United Kingdom.     

Transgenic insertional mutagenesis. Applications to inner-ear genetics

STUDY OBJECTIVE: Despite significant declines since the late 1960s, coronary mortality remains the leading cause of death for African Americans. African Americans in the US South suffer higher rates of cardiovascular disease than African Americans in other regions; yet the mortality experiences of rural-dwelling African Americans, most of whom live in the South, have not been described in detail. This study examined urban-rural differentials in coronary mortality trends among African Americans for the period 1968-86. SETTING: The United States South, comprising 16 states and the District of Columbia. STUDY POPULATION: African American men and women aged 35-74 years. DESIGN: Analysis of urban-rural differentials in temporal trends in coronary mortality for a 19 year study period. All counties in the US South were grouped into five categories: greater metropolitan, lesser metropolitan, adjacent to metropolitan, semirural, and isolated rural. Annual age adjusted mortality rates were calculated for each urban status group. In 1968, observed excesses in coronary mortality were 29% for men and 45% for women, compared with isolated rural areas. Metropolitan areas experienced greater declines in mortality than rural areas, so by 1986 the urban-rural differentials in coronary mortality were 3% for men and 11% for women. CONCLUSIONS: Harsh living conditions in rural areas of the South precluded important coronary risk factors and contributed to lower mortality rates compared with urban areas during the 1960s. The dramatic transformation from an agriculturally based economy to manufacturing and services employment over the course of the study period contributed to improved living conditions which promoted coronary mortality declines in all areas of the South; however, the most favourable economic and mortality trends occurred in metropolitan areas.     

Natural history of scoliosis in spastic cerebral palsy

BACKGROUND: Although the frequent occurrence of scoliosis in patients who have spastic cerebral palsy is well known and surgical treatment has often been recommended for these patients, little is known about the natural history of scoliosis in this population. We aimed to clarify the natural history of scoliosis from childhood through to adulthood and provide objective data on proper surgical indications for such patients. METHODS: The participants were 37 institutionalised patients with severe spastic cerebral palsy and scoliosis. All the participants had a series of radiographs taken, starting at a mean age of 7.8 years; they were followed up for an average of 17.3 years. We retrospectively reviewed radiographs and assessed the effect of five factors on progression of scoliosis: sex, degree of spasticity, initial physical capability, pattern of spinal curve, and location of curve. FINDINGS: Scoliosis usually started before the age of 10 years and progressed rapidly during the growth period. In many cases, even after growth had ended, continuous progression was seen. The mean magnitude of the curves at final examination was 55 degrees (Cobb angle). In 11 (85%) of 13 patients who had a spinal curve of more than 40 degrees before age 15 years, the scoliosis progressed to more than 60 degrees by the time of the final examination. Meanwhile, in only three (13%) of 24 patients who had a curve of less than 40 degrees at age 15 years, did the scoliosis progress to more than 60 degrees. Severe scoliosis (> or = 60 degrees) developed predominantly in those who had total body involvement (67%), were bedridden (100%), or had throacolumbar curves (57%). INTERPRETATION: The risk factors for progression of scoliosis in spastic cerebral palsy are: having a spinal curve of 40 degrees before age 15 years; having total body involvement; being bedridden; and having a thoracolumbar curve. Patients with these risk factors might benefit from early surgical intervention to prevent progression to severe scoliosis.     

Epidemiology of genital prolapse: observations from the Oxford Family Planning Association Study

OBJECTIVE: To explore the epidemiology of uterovaginal and post-hysterectomy prolapse. DESIGN: Cohort study. SETTING: Seventeen large family planning clinics in England and Scotland. POPULATION: 17,032 women who attended family planning clinics between 1968 and 1974, aged between 25 and 39 years at study entry. METHODS: Annual follow up by interview, postal or telephone questionnaire until July 1994. Further details on all hospital admissions were obtained from the hospital discharge summaries. All women were flagged at time of recruitment in the NHS central registers. MAIN OUTCOME MEASURE: In-patient admission with diagnosis of prolapse (ICD codes 8th Revision 623.0-623-9). RESULTS: The incidence of hospital admission with prolapse is 2.04 per 1000 person-years of risk. Age, parity, calendar period and weight were significantly associated with risk of an inpatient admission with prolapse after adjustment for principal confounding factors. Significant trends were observed with regard to smoking status and obesity (Quetelet Index) at entry to the study and risk of prolapse. Social class, oral contraceptive use and height were not significantly associated with risk of prolapse. The incidence of prolapse which required surgical correction following hysterectomy was 3.6 per 1000 person-years of risk. The cumulative risk rises from 1% three years after a hysterectomy to 5% 15 years after hysterectomy. The risk of prolapse following hysterectomy is 5.5 times higher (95% CI 3.1-9.7) in women whose initial hysterectomy was for genital prolapse as opposed to other reasons. CONCLUSION: Among the potential risk factors that were investigated, parity shows much the strongest relation to prolapse.     

Bilateral non-Hodgkin''s lymphoma of the breast mimicking mastitis

We recently encountered a case of recurrent non-Hodgkin's lymphoma manifested after a long period of quiescence as bilateral involvement of the breasts. This 37-year-old woman had stage IVA nodular poorly differentiated lymphocytic lymphoma diagnosed 9 years previously and was followed up without treatment. She was lost to follow-up after 4 years but had been in good health until seen with malaise and fever and pain, swelling, and erythema involving both breasts. Biopsies of lymph node and bone marrow showed a high-grade non-Hodgkin's lymphoma (lymphoblastic lymphoma) of B cell origin with central nervous system involvement. Combination chemotherapy produced a dramatic remission, but the patient died of Pseudomonas septicemia.     

Seasonal patterns of deaths in Matlab, Bangladesh

BACKGROUND: Deaths exhibit a seasonal pattern in most parts of the world. Analyses of deaths for the years 1972-1974 from the vital registration system of Matlab, Bangladesh, published in this journal 17 years ago, showed sinusoidal seasonal patterns. As death rates have declined in other nations, the seasonal pattern is attenuated. Death rates have declined substantially in Bangladesh in the past two decades. Thus, the present study examines monthly counts of deaths from Matlab data for a period 15 years later and tests the hypothesis of a decrease or shift in seasonality over time. METHODS: Trigonometric regression models were fit to monthly data by age and cause of death from the Matlab vital registration system for the years 1982-1990. A total of 20,328 death records were available for analyses. RESULTS: In the recent period significant sinusoidal seasonal patterns are found in all but one of the age and cause of death groups. Total deaths peak in the winter as do neonatal deaths but post-neonatal and child deaths are maximum in April and July respectively. Among cause groups, injury deaths (mostly attributed to drowning) show the greatest seasonal swing. The time of peak has only shifted for one age group--neonates--since the 1972-1974 period. The magnitude of the seasonal swing has declined significantly only for the neonatal age group and injury cause of death group. CONCLUSION: Marked seasonal patterns of deaths persist in the Matlab area of Bangladesh even as the level of mortality has declined.     

Contribution to the history of gerontology in Germany in the 2nd half of our century

In this paper some trends of gerontology during the last 45 years in Germany are described. A survey of the development of gerontology in the former GDR is followed by an analysis of the "Zeitschrift für Alternsforschung" from 1980-1990. The main result is the predominance of publications on the care system since the middle of the 1980s. With regard to the development of gerontology in the western part of Germany, an analysis of publications in the "Zeitsschrift für Gerontologie" from 1968-1991 shows changes in the main topics during this period. Until the middle of the 1970s there was a predominance of publications in the field of: intelligence, learning, memory and perception. The emphasis of publications from 1977-1985 was on stress and coping. In the middle of the 1980s there was an increasing interest in the analysis of social network and competence in the elderly. The paper discusses these trends of gerontological research in the eastern and western parts of Germany.     

Meningococcal disease in childhood--a regional study in Ireland

A retrospective study of microbiology laboratory records of culture-confirmed cases of meningococcal disease in children under 14 years of age, admitted to four Dublin hospitals, was conducted for the period 1981-1991 inclusive. The study aimed to describe the epidemiology of meningococcal disease in childhood and to assess the potential of meningococcal group A and C vaccine in preventing disease. There were 406 cases of meningococcal disease of which 319 (78.6%) were in children under 5 years of age. The meningitis to septicaemia ratio was almost 4:1 (320 vs. 86 cases). Of the 406 cases, 216 (53.2%) cases occurred during the period November to March. The age-specific annual incidence rates for the Eastern Health Board region served was 64.2 per 100,000 under 1 year of age and 24.6 per 100,000 under 5 years of age. A relative increase in disease caused by meningococcal serogroup C was observed during the period of the study. Only 15% all cases could have been prevented by a policy of universal meningococcal group A and C immunisation at 2 years of age. Such a policy, therefore, is not recommended. A vaccine for preventing disease caused by meningococcal group B is urgently required.     

The eradication of a large scabies outbreak using community-wide health education

The successful experience in eradicating a large outbreak of scabies in an underdeveloped Arabic village community in Western Galilee of about 3,000 people is reviewed. In this village the number of cases of scabies increased over a five-year period to a maximum of 22 per cent of the entire village population, representing 66 per cent of all the families. A seven-person health team with a strong background in health education was entrusted with the task of eradicating scabies in the community. A plan, conceived and carried out by the team, consisted of four phases: data gathering, information giving, treatment, and evaluation and summary. The goal of eradicating scabies in this community was achieved. The strategy of the campaign emphasized the following points: the entire community was the target group and was involved maximally throughout the campaign; the professional responsibility was concentrated in the hands of the team.     

Potential human and economic cost-savings attributable to vision testing policies for driver license renewal, 1989-1991

PURPOSE: This study assessed the impact of vision-related relicensing policies on traffic fatalities in the United States. There is a limited empirical basis for state vision testing policies for relicensing. Furthermore, it is uncertain whether contemporary vision standards for driver licensing achieve their implicit goal of protecting the public's health, or inappropriately restrict the mobility of competent drivers. METHODS: The 48 contiguous states and the District of Columbia were the "subjects" in this investigation. During the study period (1989 to 1991), 10 states did not require vision testing for driver license renewal. Multiple regression modeling was used to assess the impact of vision-related relicensing policies on traffic safety and to estimate the number of avoidable vehicle occupant fatalities and corresponding economic costs associated with traffic crashes involving older drivers (> or = 60 years). The primary data source for this investigation was the Fatal Accident Reporting System (FARS) database. RESULTS: Vision-related relicensing policies were significantly associated (p < 0.05) with lower vehicle occupant fatality rates of older drivers. According to the final regression model, approximately 222 fewer vehicle occupant fatalities (-12.2%) associated with older drivers would be expected for the 3-year period if mandatory vision testing policies had been in effect in 8 of the 10 states without such policies. Conservatively, those avoidable deaths represent an estimated $31 million in avoidable economic costs. CONCLUSIONS: State-level mandatory vision testing for relicensure may enhance traffic safety and reduce the economic burden of fatal crashes. Vision testing requirements should be maintained by jurisdictions with such requirements, and jurisdictions without such requirements should consider the potential traffic safety benefits of vision testing for driver license renewal.     

Opposing national stroke mortality trends in Poland and for African Americans and whites in the United States, 1968 to 1994

BACKGROUND AND PURPOSE: The United States (US) has experienced declines in stroke mortality in contrast to the increases reported for Poland. As part of the Poland and US Agreement on Cardiovascular and Cardiopulmonary Research, stroke mortality trends in Polish and US subpopulations were compared in the context of cross-population differences in competing causes of death and determinants of stroke. METHODS: Age-adjusted annual stroke, cardiovascular disease (CVD), non-CVD, and all-cause mortality rates were determined for men and women aged 35 to 64 and 65 to 74 years from 1968 to 1994 for African Americans and US whites and in Poland. Mean annual percent changes of mortality rates were estimated during 1968 to 1980 and 1981 to 1994 with the use of piecewise log-linear regression. RESULTS: US stroke mortality rates declined 3.7% to 4.8% annually during 1968 to 1980 and 2.0% to 3.1% during 1981 to 1994, with similar declines in each ethnic, gender, and age group. Polish rates increased 3.3% to 5.5% annually for all age-gender groups in Poland during 1968 to 1980. Polish men aged 35 to 64 experienced increasing rates during 1981 to 1994 (1.6% annually), while Polish women and older men experienced slight declines or little change. Only Polish men aged 35 to 64 years exhibited increases in stroke, CVD, and non-CVD mortality rates during both time intervals. CONCLUSIONS: Poland and the US experienced opposing stroke mortality rate trends between 1968 and 1994. These national and ethnic trends occurring in just one generation suggest major effects of lifestyle, socioenvironmental, and/or medical care determinants.     

Biliary strictures in hepatic transplantation: treatment with self-expanding Z stents

Excellent and good results following different operations for TOS are close to 80%, using simple statistics, where results included many patients followed up for only a few months. Using life-table methods, the success rate is 6% to 9% less, close to 70%, at 5 years. The results were virtually identical for anterior and middle scalenectomy, transaxillary first rib resection, and combined supraclavicular scalenectomy and first rib resection. Secondary success, the results of reoperation on patients in whom the first operation failed, improved the results of the primary operation 15% and 17%, respectively, for transaxillary rib resection and anterior and middle scalenectomy. When the initial operation was combined rib resection and scalenectomy, fewer patients underwent reoperation, as only neurolysis could be performed, and the results improved only 3%. A significant variable in results was etiology: Work-related injuries versus non-work-related accidents, usually auto accidents. Results of three independent studies showed better success rates by 13% to 15%, in patients who had non-work-related auto accidents, as compared with work-related injuries.     

Applying the realized probability of dying to cancer survival

Age comparisons of survival in cancer cohorts generally utilize relative survival rates, which are based on indicators of the probability of survival for a given number of years after diagnosis. Cancer relative survival rates for the same number of years tend to decline as age at diagnosis increases. However, the same number of years of survival reflects higher relative longevity at older ages than at younger ages. The realized probability of dying (RPD) is a survival measure that expresses individual survival time after diagnosis relative to the survival distribution of an age-, race-, and sex-specific reference population, in effect weighing individual survival time more heavily as age at diagnosis increases. The purpose of this study was to apply the RPD as a survival measure in cancer epidemiology. Two cohorts of cancer patients, white males with prostate cancer and white females with breast cancer, aged 55 years and over at diagnosis, were followed for 15 years. Although older subjects survived less time after diagnosis than younger subjects, they achieved more favorable RPD values. We present survival analysis methods for analyzing the RPD in this population, an approach not previously used with this measure. The implications for use of the RPD in cancer epidemiology are discussed.     

Number and timing failures among legitimate births in the United States: 1968, 1969 and 1972

More than one in 10 legitimate births that occurred in the United States during 1968, 1969, and 1972 were not wanted at all, and more than one-quarter of the births were timing failures. A substantial reduction in unwanted childbearing took place between 1968 and 1972. The proportion of legitimate births reported by their mothers to be unwanted ever declined from 13 percent in 1968 to eight percent in 1972. If, as reported in a number of cross-sectional surveys taken during this approximate period, there was a sharp reduction in wanted family size reported by married women, then these women would have remained at risk of having an unwanted birth for a longer period than when their wanted family size had been higher. Thus, these estimates of a decline in unwanted childbearing may be understated (although there was the countervailing trend of later age at marriage during these years). The decline in unwanted childbearing between 1968 and 1972 is only partially attributable to the shift toward lower birth orders that occurred. Declines in unwanted births occurred for almost all birth orders. There was no significant reduction in mistimed births. Because the decline in unwanted fertility during the study period was much greater for nonwhites than whites, the traditional racial differential in unwanted childbearing narrowed considerably between 1968 and 1972. In 1968, 12 percent of the white legitimate births were classified as not wanted, compared to 21 percent of the legitimate births to nonwhites. However, between 1968 and 1972, nonwhites experienced extremely sharp declines in unwanted childbearing. Thus, in 1972 only 9.5 percent of the legitimate births to nonwhites were reported as unwanted, compared to 8.1 percent of the white births. Mothers of higher parity were much more likely to report a birth as unwanted than those of lower parity. Mothers who had completed more schooling were less likely than poorly educated mothers to report births as unwanted. Income level seems unrelated to whether the birth is unwanted, but is inversely related to whether it is a timing failure. Births that resulted from premarital conceptions tended to be reported as timing failures. Viewed from the cross-sectional perspective of period rates of population change, the elimination of unwanted legitimate childbearing would have had a substantial effect on population growth in each of the study years even without decreasing marital mistimed births or illegitimate fertility. The data also suggest that eliminating unwanted marital childbearing could significantly reduce completed family size. However, this conclusion must be viewed with great caution, since we do not know the future variations in timing and spacing of births, and the extent to which the childbearing experience of the sampled mothers is representative of their birth cohorts.