Follow-up methods for retrospective cohort studies in New Zealand

Objectives: To define a general methodology for maximising the success of follow-up processes for retrospective cohort studies in New Zealand, and to illustrate an approach to developing country-specific follow-up methodologies.
Methods: We recently conducted a cohort study of mortality and cancer incidence in New Zealand professional fire fighters. A number of methods were used to trace vital status, including matching with records of the New Zealand Health Information Service (NZHIS), pension records of Work and Income New Zealand (WINZ), and electronic electoral rolls. Non-electronic methods included use of paper electoral rolls and the records of the Registrar of Births Deaths and Marriages.
Results: 95% of the theoretical person-years of follow-up of the cohort were traced using these methods. In terms of numbers of cohort members traced to end of follow-up, the most useful tracing methods were fire fighter employment records, the NZHIS, WINZ, and the electronic electoral rolls.
Conclusions: The follow-up process used for the cohort study was highly successful. On the basis of this experience, we propose a generic, but flexible, model for follow-up of retrospective cohort studies in New Zealand. Similar models could be constructed for other countries.
Implications: Successful follow-up of cohort studies is possible in New Zealand using established methods. This should encourage the use of cohort studies for the investigation of epidemiological issues. Similar models for follow-up processes could be constructed for other countries.     

THE DEVELOPMENT OF A NEW ZEALAND TWIN REGISTER

Large-scale twin registers have been used in several countries for epidemiological studies of chronic diseases. They make possible an analysis of the health effects of environmental factors while genetic factors are controlled. A twin register comprising all live nuptial non-Maori twins born in 1926 to 1935 in New Zealand was developed. The total number of multiple births was 2765 (with 2750 twin births) giving a multiple birth ratio of 1.1 per cent of live births. About one third each of the twin pairs were mixed-sex, male and female pairs. After a multi-stage record search process 1998 pairs had been traced to an address or a death record and an additional 580 pairs had one twin traced. The neonatal mortality rate for the twins was about 8 per cent, much higher than the 2.4 per cent reported for all births in 1930. The current addresses of the twins were searched in electoral rolls and a total of 1428 pairs where both are alive have been located. It is planned to collect base-line environmental exposure data with an internationally agreed questionnaire and to follow-up the mortality of the twins in the future.     

Tracing 8,600 participants 36 years after recruitment at age seven for the Tasmanian Asthma Study

OBJECTIVE: To trace all participants 36 years after the original Tasmanian Asthma Study (TAS). METHODS: In 1968, the TAS investigated asthma in 8,583 children who were born in 1961. We attempted to trace these participants in 2002-04 using names, dates of birth and gender. Current addresses were sought by computer linkage to the Commonwealth Electoral Roll, the Medicare database and the Tasmanian marriage records. Computer linkage was conducted with the National Death Index (NDI). Siblings of participants were also linked to the Commonwealth Electoral Roll and those identified were sent a letter requesting the participant's address. The Australian Twin Registry (ATR) and the 1991-93 TAS substudy were used to locate participant addresses. RESULTS: After three rounds of electoral roll linkage, 56% of all cohort members were traced. Name changes were identified for 49% of the 3,477 females not initially matched to the electoral roll using linkage to marriage records. NDI linkage yielded a 0.7% match. Medicare linkage identified addresses for 27% of the 1,982 remaining participants. Writing to siblings located 60% of 1,661 participants. One hundred and eighty-three participants were matched to the 1991-93 TAS and 23 twins matched to the ATR. Overall, 81.5% of the cohort members were identified. CONCLUSIONS: With these methods, we have been able to trace a possible address for a large portion of the original participants, with the electoral roll linkage being the most useful. IMPLICATIONS: It is possible to trace Australians for follow-up studies using electronic linkage, although without unique identifiers it is labour and resource intensive and requires matching to several databases.     

The long history of health inequality in New Zealand: occupational class and lifespan in the late 1800s and early 1900s

Objective: As relatively little is known about how socioeconomic position might have affected health prior to the Second World War, we aimed to study lifespan by occupational class in two cohorts in New Zealand. Methods: The first study included men on the electoral rolls in Dunedin in the period 1893 to 1902. The second study used an established cohort of male military personnel who were recruited for the First World War. Linear regression was used to estimate lifespan by occupational class. Results: The first study of 259 men on the electoral rolls found no substantive lifespan differences between the high and low occupational class groups. But the second study of 2,406 military personnel found that men in the three highest occupational classes lived 3.5 years longer (95%CI: 0.3–6.8 years) than the three lowest classes (in the multivariable analysis adjusting for age in 1918 and rurality of occupation). Conclusions: We found no significant lifespan differences in one cohort, but a second cohort is the earliest demonstration to our knowledge of substantial differences in mortality by socioeconomic position in this country prior to the 1960s. Implications for public health: This study provides historical context to the long‐term efforts to address health inequalities in society.     

A Kaupapa Māori approach to a community cohort study of heart disease in New Zealand

Objective: To report the processes and protocols that were developed in the design and implementation of the Hauora Manawa Project, a cohort study of heart disease in New Zealand and to report the participation at baseline. Methods: This study utilised application of a Kaupapa Māori Methodology in gaining tribal and health community engagement, design of the project and random selection of participants from territorial electoral rolls, to obtain three cohorts: rural Māori, urban Māori and urban non‐Māori. Logistic regression was used to model response rates. Results: Time invested in gaining tribal and health community engagement assisted in the development and design of clear protocols and processes for the study. Response rates were 57.6%, 48.3% and 57.2%. Co‐operation rates (participation among those with whom contact was established) were 74.7%, 66.6% and 71.4%. Conclusions: Use of electoral rolls enables straightforward sampling but results in low response rates because electors have moved. Co‐operation rates highlight the acceptability of this research project to the participants; they indicate the strength of Kaupapa Māori Methodologies in engaging Māori participants and community. Implications: This study provides a model for conducting clinical/biomedical research projects that are compatible with cultural protocols and methodologies, in which the primary aim of the research was Māori health gain.     

Is testicular cancer an occupational disease of fire fighters?*

BACKGROUND: A previous investigation showed an increased risk of testicular cancer among fire fighters in Wellington City, New Zealand, during the 1980s. Other studies of fire fighters had not identified testicular cancer as an occupational disease. METHODS: This was an historical cohort study of mortality and cancer incidence in all paid New Zealand fire fighters, from 1977 to 1995. RESULTS: The only cancer for which this study provided evidence of an increased risk was testicular cancer, even after excluding cases from the previous investigation. The standardized incidence ratio for 1990-96 was 3.0 (95% confidence interval: 1.3-5.90). There was no evidence that fire fighters were at increased risk from any particular cause of death. CONCLUSIONS: This study confirmed that New Zealand fire fighters are at increased risk of testicular cancer, although the reason is unknown. Other incidence studies of cancer in fire fighters are needed to confirm this finding.     

Health effects of dental amalgam exposure: a retrospective cohort study

BACKGROUND: Whether dental amalgam fillings (containing mercury) are hazardous is a long-standing issue, with few epidemiological investigations. Allegations have particularly involved nervous system disorders, such as multiple sclerosis, Alzheimer's disease, and chronic fatigue syndrome. This retrospective cohort study, the largest of its kind, contained people in the New Zealand Defence Force (NZDF) between 1977 and 1997. The NZDF has its own dental service, providing all personnel with regular and consistent treatment. Comprehensive treatment records are maintained and archived. METHODS: Yearly dental treatment histories, including amalgam filling placements, were compiled from individual records. To minimize amalgam exposure misclassification the cohort was restricted to people who, at NZDF entry, were aged <26 years and had all their posterior teeth. The cohort was linked with morbidity records. Data were analysed with a proportional hazards model, using a time-varying exposure unit of 100 amalgam surface-years. RESULTS: The final cohort contained 20 000 people, 84% males. Associations with medical diagnostic categories, particularly disorders of the nervous system and kidney, were examined. Of conditions allegedly associated with amalgam, multiple sclerosis had an adjusted hazard ratio (HR) of 1.24 (95% CI: 0.99, 1.53, P = 0.06), but there was no association with chronic fatigue syndrome (HR = 0.98, 95% CI: 0.94, 1.03), or kidney diseases. There were insufficient cases for investigation of Alzheimer's or Parkinson's diseases. CONCLUSIONS: Results were generally reassuring, and provide only limited evidence of an association between amalgam and disease. Further follow-up of the cohort will permit investigation of diseases more common in the elderly.     

Just what the doctor ordered: Moving forward with electronic health records

Aim: To provide dietitians with information on the proposed introduction of electronic medical records in Australia and New Zealand and discuss potential benefits and challenges. Methods: An overview of the current status regarding electronic health (e‐health) records is given along with suggestions on how dietitians may like to become involved. Information was obtained by literature review and through contact with the National E‐Health Transition Authority in Australia and the National Health Information Technology Board in New Zealand. Results: Governments in both Australia and New Zealand are dedicated to the establishment of national electronic health record systems. Current issues in founding such a system include interoperability with existing systems, privacy concerns and the use of standardised terminologies. Conclusion: Integrated and practical e‐health records are an important part of an efficient and sustainable health system. Dietitians wishing to be involved can learn about the International Dietetics and Nutrition Terminology, actively seek and contribute to technology discussions in their workplace and register with available e‐health record initiatives.     

Current and future economic burden of osteoporosis in New Zealand

Background

Osteoporosis is recognized as a serious health condition in developed as well as developing countries. There are no accurate estimates of the extent of the burden of osteoporosis in New Zealand. The purpose of this study was to estimate the economic burden of osteoporosis in New Zealand using data from international studies and population and health services information from New Zealand.

Objective

To estimate the number of osteoporotic fractures and cost of treatment and management of osteoporosis and osteoporotic fractures to the health system in New Zealand in 2007 and to project the future burden in 2013 and 2020.

Methods

Hospitalizations for hip fractures were combined with New Zealand census data and estimates from previous studies to estimate the expected number of osteoporotic vertebral, humeral, pelvic and other sites fractures in 2007. Health services usage and costs were estimated by combining data from New Zealand hospitals, the New Zealand Health Survey on the number of people diagnosed with osteoporosis, and the New Zealand Health Information Service (NZHIS) on pharmaceutical treatments. All prices are in New Zealand dollars ($NZ), year 2007 values. Losses in QALYs resulting from osteoporotic fractures were used to indicate the impact on morbidity and mortality. The lost QALYs and economic cost associated with osteoporosis were projected to 2013 and 2020 using population projections from the New Zealand census.

Results

There were an estimated 84 354 osteoporotic fractures in New Zealand in 2007, including 3803 hip and 27994 vertebral fractures. Osteoporosis resulted in a loss of 11249 QALYs. The total direct cost of osteoporosis was $NZ330 million, including $NZ212 million to treat the fractures, $NZ85 million for care after fractures and $NZ34 million for treatment and management of the estimated 70 631 people diagnosed with osteoporosis. Sensitivity analysis suggested the results were robust to assumptions regarding the number of fractures receiving medical treatment. Hospitalization costs represented a significant component of total costs. The cost of treatment and management of osteoporosis is expected to increase to over $NZ391 million in 2013 and $NZ458 million in 2020, with the number of QALYs lost increasing to 13 205 in 2013 and 15 176 in 2020.

Conclusions

Osteoporosis and osteoporotic fractures create a significant burden on the health system in New Zealand. This study highlights the significant scope of the burden of osteoporosis and the potential gains that might be made from introducing interventions to mitigate the burden.     

Locating members of a cohort identified retrospectively from limited data in 50-year-old records: successful approaches employed by the Hanford Thyroid Disease Study

PURPOSE: Long-term follow-up studies sometimes rely on retrospective identification of the cohort to be followed. Few such studies have been conducted, however, that rely on very old source records, perhaps because of concern that identification and location of a cohort based on very old records would not be feasible. METHODS: The Hanford Thyroid Disease Study (HTDS), conducted in the 1990s, identified 5199 cohort members using Washington state birth records from 1940-1946. The limited information contained therein was used to trace cohort members to the present day, nearly 50 years later. RESULTS: We found the best strategy to locate individuals efficiently is to use a combination of methods and resources in a phased approach, beginning with readily available and easy-to-use sources of information before employing more time-intensive strategies that are costly and rely on information that is difficult to obtain. Motor vehicle licensing records and directories were the most useful individual sources of information. Using this approach, the HTDS successfully located 94% of the 5199 cohort members identified. CONCLUSIONS: It is feasible to successfully trace and locate a very high proportion of individuals identified from very old records that contain little information.     

Faster self-reported speed of eating is related to higher body mass index in a nationwide survey of middle-aged women

This study is the first nationwide population survey to explore the association between speed of eating and degree of obesity. The objective was to cross-sectionally examine the relationship between self-reported speed of eating and body mass index (BMI; calculated as kg/m²) in a nationally representative sample of New Zealand women. In May 2009, a sample of 2,500 New Zealand women aged 40 to 50 years was randomly selected from the nationwide electoral rolls. A 66% participation rate was achieved. Potential participants were mailed a self-administered questionnaire containing questions on self-reported speed of eating, demographics, health conditions, menopause status, physical activity, height, and weight. Univariate models were used to examine the associations between demographic, health and behavioral variables, and BMI, while a multivariate model was developed to investigate the relationship between self-reported speed of eating and BMI. After adjusting for age, smoking status, menopause status, thyroid condition, ethnicity, socioeconomic status, and physical activity, BMI statistically significantly increased by 2.8% (95% confidence interval: 1.5% to 4.1%; P<0.001) for each category increase in self-reported speed of eating. Although the direction of causality requires confirmation in longitudinal and randomized intervention studies, the results suggest that faster eating is associated with higher BMI in middle-aged women.     

Increasing geographical inequalities in health in New Zealand, 1980-2001

BACKGROUND: Recent studies have noted widening health inequalities between rich and poor areas in a number of OECD countries. This paper examines whether health in New Zealand has become more geographically polarized during the period 1980-2001, a time of rapid social and economic changes in New Zealand society. METHODS: Mortality records for each year between 1980 and 2001 were extracted for consistent geographical areas: the 21 District Health Boards operating in New Zealand in 2001 and used to calculate male and female life expectancies for each area. The geographical inequalities in life expectancy were measured by calculating the slope index of inequality for each year between 1980 and 2001. RESULTS: Although overall life expectancy has increased during the period of study, New Zealand has experienced increased spatial polarization in health, with a particularly sharp rise in inequality during the late 1980s and early 1990s. Since the mid-1990s regional inequality has remained at stable but high levels. The polarization in mortality was mirrored by a growth in income inequality during the 1980s and 1990s. CONCLUSIONS: Health inequalities as expressed geographically in New Zealand have reached historically high levels and show little sign of abating. In order to tackle health inequalities, a greater commitment by the New Zealand government to a more redistributive social and economic agenda is required. Furthermore, issues of differentiated and health selective migration, emigration, and immigration need to be addressed as if these are important they should matter more for New Zealand than for almost any other developed nation-state.     

Tracking Australian health and medical research expenditure with a PubMed bibliometric method

Objective: To assess Australian health and medical research (HMR) investment returns by measuring the trends in HMR expenditure and PubMed publications by Australian authors. Methods: Bibliometric analysis collating Australian HMR expenditure reported by the Australian Institute of Health and Welfare and Australian HMR publications indexed in PubMed. Similar methods were applied to data from the United Kingdom and New Zealand. Results: From financial year 2000/01 through 2011/12, HMR investment increased by 232% from $1.49 to $4.94 billion (current prices adjusted for inflation), while PubMed publications increased by 123% from 10,696 to 23,818. The average HMR investment required for a single PubMed publication rose by 49% from $139,304 in 2000/01 to $207,364 in 2011/12. Quality analyses showed an increase in systematic reviews, cohort studies and clinical trials, and a decrease in publications in PubMed's core clinical journal collection. Comparisons with New Zealand and the United Kingdom showed that Australia has had the greatest overall percentage increase in gross publication numbers and publications per capita. Conclusions: Our analyses confirm that increased HMR expenditure is associated with an increase in HMR publications in PubMed. Implications: Tracking HMR investment outcomes using this method could be useful for future policy and funding decisions at a federal and specific institution level.     

School milk and risk of colorectal cancer: a national case-control study

To determine whether school milk consumption in childhood decreased the risk of adult colorectal cancer, the authors conducted a national population-based, case-control study of 562 cases and 571 controls. The authors identified new cases of colorectal cancer in 2007 among people aged 30-69 years from the New Zealand Cancer Registry. Controls were randomly selected from the electoral rolls and frequency matched to cases in 5-year age groups. Participation in school milk programs was associated with a reduced odds ratio for colorectal cancer (odds ratio (OR) = 0.70, 95% confidence interval (CI): 0.51, 0.96). Odds ratios decreased with increasing numbers of bottles of milk drunk compared with no school milk (for 1-799 bottles, OR = 1.04, 95% CI: 0.66, 1.67; for 800-1,199 bottles, OR = 0.81, 95% CI: 0.51, 1.29; for 1,200-1,599 bottles, OR = 0.62, 95% CI: 0.41, 0.93; for 1,600-1,799 bottles, OR = 0.57, 95% CI: 0.37, 0.90; and for 1,800 or more bottles, OR = 0.62, 95% CI: 0.41, 0.96). Participation in school milk programs in New Zealand was associated with a 2.1% reduction (95% CI: 0.7, 3.5) in the odds ratio for colorectal cancer for every 100 half-pint bottles drunk (1 half-pint bottle = 284 mL).     

Resource management in New Zealand hospitals: the RUS (resource utilization system) system--an illustration of its applications

This study demonstrates a potential application in the planning and policy area of a resource management system (known as the Resource Utilisation System (RUS)) first introduced into New Zealand in 1987 and now becoming the definitive resource management tool in the New Zealand public hospital sector. A retrospective cohort of 193 individuals (mean age 60.2 years, 73% males) admitted to Dunedin Public hospital with their first acute myocardial infarction in 1978 was followed through for 10 years in order to describe their inpatient resource utilisation as well as their morbidity and mortality experience. The cumulative mortality for the group over 10 years was 57%. The potential years of life lost (PYLL) amounted to 1340 years, or 6.9 years per person. The overall inpatient resource utilisation amounted to $2,317,300 for the whole group, or $12,006 per person (1988 NZ dollars) over the 10 years follow-up.     

Injury hospitalization and risks for subsequent self-injury and suicide: a national study from New Zealand

OBJECTIVES: Risks for suicide and nonfatal self-injury hospitalizations associated with previous injury hospitalizations were investigated in a nationwide retrospective cohort study conducted in New Zealand. METHODS: Linked data from all New Zealand public hospitals were used to identify individuals with injury hospitalizations. Participants were followed for 12 months. RESULTS: Significantly increased age- and sex-adjusted relative risks for suicide were associated with previous hospitalization for self-injury, injuries of undetermined causes, and assault. Also, elevated risks were associated with these causes of hospitalization in the case of subsequent self-injury hospitalizations. CONCLUSIONS: Results indicate that identifiable subgroups of individuals hospitalized for injuries are at marked risk for serious suicidal behavior and suggest the potential of targeted suicide prevention for these individuals.     

Motor vehicle driver injury and socioeconomic status: a cohort study with prospective and retrospective driver injuries

STUDY OBJECTIVE: To investigate the association between motor vehicle driver injury and socioeconomic status. DESIGN: Cohort study with prospective and retrospective outcomes. SETTING: New Zealand. PARTICIPANTS: 10 525 adults (volunteer sample of a multi-industry workforce, n=8008; and a random sample of urban electoral rolls, n=2517). Outcome measure: Motor vehicle driver injury resulting in admission of the driver to hospital or the driver's death, or both, during the period 1988-98; hospitalisation and mortality data were obtained by record linkage to national health databases. Main results: After adjustment for age and sex, driver injury risk was inversely associated with both occupational status (p for linear trend <0.0001) and educational level (p for linear trend =0.007). Participants in the lowest approximate quartile of occupational status were four times as likely (HR 4.17, 95% CI 2.31 to 7.55) to have experienced a driver injury during follow up as participants in the highest approximate quartile. Participants who had been to secondary school for less than two years were twice as likely (HR 2.26, 95% CI 1.34 to 3.81) to have experienced a driver injury as those who had been to university or polytechnic. There was little evidence that driver injury risk was associated with neighbourhood income (p for linear trend =0.12) CONCLUSIONS: Occupational status and educational level seem to be important determinants of driver injury risk. Driver injury countermeasures should be targeted to people in low status occupations, as well as to people with comparatively little formal education.     

The New Zealand Asthma and Allergy Cohort Study (NZA<Superscript>2</Superscript>CS): Assembly,Demographics and Investigations

Background  

Asthma and allergy are highly prevalent in industrialised countries. Longitudinal and cross-sectional studies have identified a number of potential risk factors for these conditions, including genetic and environmental factors, with significant gene-environment relationships. Birth cohort studies have been proposed as an important tool to explore these risk factors, particularly exposures in early life that are associated with later disease or protection from disease. This paper describes the establishment of a birth cohort in New Zealand.     

Measuring the 'obesogenic' food environment in New Zealand primary schools

Childhood obesity is an increasing health problem in New Zealand and many other countries. Information is needed to guide interventions that reduce the 'obesogenic' (obesity-promoting) elements of school environments. The aim of this study was to identify and measure the obesogenic elements of the school environment and the canteen sales of energy-dense foods and drinks. A self-completion questionnaire was developed for assessing each school's nutrition environment and mailed to a stratified random sample of New Zealand schools. The responses from primary schools (n = 200, response rate 61%) were analysed. Only 15.5% of schools had purpose-built canteen facilities and over half ran a food service for profit (31% profit to the school, 24.5% profit for the contractors). Only 16.5% of schools had a food policy, although 91% of those rated the policy as effective or very effective. The most commonly available foods for sale were pies (79%), juice (57%) and sausage rolls (54.5%). Filled rolls were the most expensive item (mean dollars 1.79) and fruit the least expensive (mean dollars 0.47). The ratio of 'less healthy' to 'more healthy' main choices was 5.6:1, for snacks it was 9.3:1 and for drinks it was 1.4:1. In contrast, approximately 60% of respondents said that nutrition was a priority for the school. Only 50% felt there was management support for healthy food choices and only 39% agreed that mainly nutritious food was offered by the food service. 'Less healthy' choices dominated food sales by more than 2:1, with pies being the top selling item (>55000 per week). We found that the food environment was not conducive to healthy food choices for the children at New Zealand schools and that this was reflected in the high sales of relatively unhealthy foods from the school food services. Programmes that improve school food through policies, availability, prices and school ethos are urgently needed.