Data Linkage: Canadian and Australian Perspectives on a Valuable Methodology for Intellectual and Developmental Disability Research.

Data linkage holds great promise for generating new information about people with intellectual and developmental disabilities (IDD) as a population, yet few centers have developed the infrastructure to utilize this methodology. Two examples, from Canada and Australia, describe their efforts in building data linkage capabilities, and how linked databases can be used to identify persons with IDD and used for population-based research. The value of data linkage is illustrated through new estimates of prevalence of IDD; health service utilization patterns; associations with sociodemographic characteristics, and with physical and mental health conditions (e.g., chronic diseases, injury, fertility, and depression); and findings on equity in medical treatments. Examples are provided of findings used for governmental policy and program planning.

Impact of first and second eye cataract surgery on physical activity: a prospective study.

OBJECTIVES: To investigate the impact of first eye and second eye cataract surgery on the level of physical activity undertaken by older adults with bilateral cataract. DESIGN: Prospective cohort study. SETTING: Three public ophthalmology clinics in Western Australia. PARTICIPANTS: Fifty-five older adults with bilateral cataract aged 55+ years, awaiting first eye cataract surgery. OUTCOME MEASURES: The primary outcome measure was participation in moderate leisure-time physical activity. The secondary outcomes were participation in walking, gardening and vigorous leisure-time physical activity. Participants completed a researcher-administered questionnaire, containing the Active Australia Survey and visual tests before first eye cataract surgery, after first eye surgery and after second eye surgery. A Generalised Estimating Equation linear regression model was undertaken to analyse the change in moderate leisure-time physical activity participation before first eye surgery, after first eye surgery and after second eye surgery, after accounting for relevant confounders. RESULTS: Participants spent significantly less time per week (20 min) on moderate leisure-time physical activity before first eye cataract surgery compared with after first eye surgery (p=0.04) after accounting for confounders. After second eye cataract surgery, participants spent significantly more time per week (32 min) on moderate physical activity compared with after first eye surgery (p=0.02). There were no significant changes in walking, gardening and vigorous physical activity throughout the cataract surgery process. CONCLUSION: First and second eye cataract surgery each independently increased participation in moderate leisure-time physical activity. This provides a rationale for timely first and second eye cataract surgery for bilateral cataract patients, even when they have relatively good vision.

The impact of first- and second-eye cataract surgery on motor vehicle crashes and associated costs.

Objective: to evaluate the association between first- and second-eye cataract surgery and motor vehicle crashes for older drivers and the associated costs to the community. Design: retrospective population-based cohort study. Subjects: a total of 2,849 drivers aged 60 years and older who had undergone both first- and second-eye cataract surgery were involved in 3,113 motor vehicle crashes as drivers during the study period. Methods: de-identified data were obtained using the Western Australian Data Linkage System from 1 January 2003 to 31 December 2015. Poisson regression analysis based on Generalised Estimating Equations was undertaken to compare the frequency of crashes in the year before first eye cataract surgery, between first and second eye surgery and 1 year after second eye surgery. Results: first eye cataract surgery was associated with a significant 61% reduction in crash frequency (P < 0.001) and second eye surgery was associated with a significant 23% reduction in crashes (P < 0.001), compared to the year before first eye cataract surgery after accounting for age, gender, marital status, accessibility, socio-economic status, driving exposure and comorbidities. The estimated cost savings from the reduction in crashes in the year after second eye cataract surgery compared to the year before first eye cataract surgery was $14.9 million. Conclusions: first- and second-eye cataract surgery were associated with a significant reduction in motor vehicle crashes, with first eye surgery having the greatest impact. These results provide encouragement for the timely provision of first- and second-eye cataract surgery for older drivers.

Morbidity burden and community-based palliative care are associated with rates of hospital use by people with schizophrenia in the last year of life: A population-based matched cohort study.

OBJECTIVE: People with schizophrenia face an increased risk of premature death from chronic diseases and injury. This study describes the trajectory of acute care health service use in the last year of life for people with schizophrenia and how this varied with receipt of community-based specialist palliative care and morbidity burden. METHOD: A population-based retrospective matched cohort study of people who died from 01/01/2009 to 31/12/2013 with and without schizophrenia in Western Australia. Hospital inpatient, emergency department, death and community-based care data collections were linked at the person level. Rates of emergency department presentations and hospital admissions over the last year of life were estimated. RESULTS: Of the 63508 decedents, 1196 (1.9%) had a lifetime history of schizophrenia. After adjusting for confounders and averaging over the last year of life there was no difference in the overall rate of ED presentation between decedents with schizophrenia and the matched cohort (HR 1.09; 95%CI 0.99-1.19). However, amongst the subset of decedents with cancer, choking or intentional self-harm recorded on their death certificate, those with schizophrenia presented to ED more often. Males with schizophrenia had the highest rates of emergency department use in the last year of life. Rates of hospital admission for decedents with schizophrenia were on average half (HR 0.53, 95%CI 0.44-0.65) that of the matched cohort although this varied by cause of death. Of all decedents with cancer, 27.5% of people with schizophrenia accessed community-based specialist palliative care compared to 40.4% of the matched cohort (p<0.001). Rates of hospital admissions for decedents with schizophrenia increased 50% (95% CI: 10%-110%) when enrolled in specialist palliative care. CONCLUSION: In the last year of life, people with schizophrenia were less likely to be admitted to hospital and access community-based speciality palliative care, but more likely to attend emergency departments if male. Community-based specialist palliative care was associated with increased rates of hospital admissions.

The impact of first and second eye cataract surgeries on falls: a prospective cohort study.

PURPOSE: The purpose of this study was to investigate the impact of the first and second eye cataract surgeries on the risk of falls in participants with bilateral cataract and to determine which changes in visual measures are associated with changes in the number of falls throughout the cataract surgery process. PATIENTS AND METHODS: Fifty-five older adults with bilateral cataract aged 55+ years were assessed at three time points during the cataract surgery process, and they completed a falls diary. Two separate generalized estimating equation-negative binomial models were undertaken to assess changes in the number of falls before first eye cataract surgery, between first and second eye surgeries, and after second eye cataract surgery and which changes in visual measures were associated with changes in the number of falls. RESULTS: After adjusting for potential confounding factors, the risk of falls decreased by 54% (incidence rate ratio (IRR) =0.458, 95% CI=0.215-0.974, p=0.04) after first eye cataract surgery only, compared with the period before first eye surgery. The risk of falls decreased by 73% (IRR =0.268, 95% CI =0.114-0.628, p=0.002) after second eye cataract surgery, compared with the period before first eye surgery. Improved binocular visual acuity (IRR =5.488, 95% CI =1.191-25.282, p=0.029) and contrast sensitivity (IRR =0.257, 95% CI =0.070-0.939, p=0.040) were associated with a decrease in the number of falls. CONCLUSION: The study found that first and second eye cataract surgeries reduced the risk of falls among a cohort of bilateral cataract patients with relatively good baseline vision. This suggests that timely first and second eye cataract surgeries could play an important role in reducing the burden due to falls among older adults with cataract.

Use of health services in the last year of life and cause of death in people with intellectual disability: a retrospective matched cohort study.

OBJECTIVE: To describe the cause of death together with emergency department presentations and hospital admissions in the last year of life of people with intellectual disability. METHOD: A retrospective matched cohort study using de-identified linked data of people aged 20 years or over, with and without intellectual disability who died during 2009 to 2013 in Western Australia. Emergency department presentations and hospital admissions in the last year of life of people with intellectual disability are described along with cause of death. RESULTS: Of the 63 508 deaths in Western Australia from 2009 to 2013, there were 591 (0.93%) decedents with a history of intellectual disability. Decedents with intellectual disability tended to be younger, lived in areas of more social disadvantage, did not have a partner and were Australian born compared with all other decedents. A matched comparison cohort of decedents without intellectual disability (n=29 713) was identified from the general population to improve covariate balance.Decedents with intellectual disability attended emergency departments more frequently than the matched cohort (mean visits 3.2 vs 2.5) and on average were admitted to hospital less frequently (mean admissions 4.1 vs 6.1), but once admitted stayed longer (average length of stay 5.2 days vs 4.3 days). People with intellectual disability had increased odds of presentation, admission or death from conditions that have been defined as ambulatory care sensitive and are potentially preventable. These included vaccine-preventable respiratory disease, asthma, cellulitis and convulsions and epilepsy. CONCLUSION: People with intellectual disability were more likely to experience potentially preventable conditions at the end of their lives. This indicates a need for further improvements in access, quality and coordination of healthcare to provide optimal health for this group.

Psychotropic Medication and Substance Use during Pregnancy by Women with Severe Mental Illness.

BACKGROUND: Sociodemographic factors, alcohol and drug intake, and maternal health are known to be associated with adverse outcomes in pregnancy for women with severe mental illness in addition to their use of psychotropic medication. In this study, we describe the demographic characteristics of women hospitalized for severe mental illness along with their use of medication and other drugs during the pregnancy period. METHODS: A clinical case note review of women with psychosis who were hospitalized at the State Psychiatric Hospital in Western Australia during 1966-1996, gave birth between 1980 and 1992, and received psychiatric treatment during the pregnancy period. The mother's clinical information was available from the case notes and the midwives record. The demographic characteristics of the mothers were described together with their hospitalization pattern and their medication and substance use during the pregnancy period. RESULTS: A total of 428 mothers with a history of severe mental illness were identified who gave birth during 1980-1992. Of these, 164 mothers received psychiatric care during the pregnancy period. One hundred thirty-two had taken psychotropic medication during this period. Mothers who were married, of aboriginal status or living in regional and remote areas appeared less likely to be hospitalized during the pregnancy period, while older mothers and those with a diagnosis of schizophrenia were more likely to be hospitalized. The number of mothers taking psychotropic medication in the first trimester of pregnancy was reduced compared to the previous 6 months. The decline in the number taking substances over the same period was not significant. In all, 16% of the women attempted suicide during the pregnancy period and 10% non-suicidal self-injury. CONCLUSION: The women demonstrate a pattern of decreased use of psychotropic medication use from the period before pregnancy to the first trimester of pregnancy. Our data highlight the importance of women with severe mental illness receiving regular ongoing monitoring and support from their psychiatrist during pregnancy regarding the level of medication required as well as counseling with regard to substance use, non-suicidal self-injury, and attempted suicide.

Issues using linkage of hospital records and death certificate data to determine the size of a potential palliative care population.

BACKGROUND: Studies aiming to identify palliative care populations have used data from death certificates and in some cases hospital records. The size and characteristics of the identified populations can show considerable variation depending on the data sources used. It is important that service planners and researchers are aware of this. AIM: To illustrate the differences in the size and characteristics of a potential palliative care population depending on the differential use of linked hospital records and death certificate data. DESIGN: Retrospective cohort study. SETTING/PARTICIPANTS: The cohort consisted of 23,852 people aged 20 years and over who died in Western Australia between 1 January 2009 and 31 December 2010 after excluding deaths related to pregnancy or trauma. Within this cohort, the number, proportion and characteristics of people who died from one or more of 10 medical conditions considered amenable to palliative care were identified using linked hospital records and death certificate data. RESULTS: Depending on the information source(s) used, between 43% and 73% of the 23,852 people who died had a condition potentially amenable to palliative care identified. The median age at death and the sex distribution of the decedents by condition also varied with the information source. CONCLUSION: Health service planners and researchers need to be aware of the limitations when using hospital records and death certificate data to determine a potential palliative care population. The use of Emergency Department and other administrative data sources could further exacerbate this variation.

The collective impact of rare diseases in Western Australia: an estimate using a population-based cohort.

PURPOSE: It has been argued that rare diseases should be recognized as a public health priority. However, there is a shortage of epidemiological data describing the true burden of rare diseases. This study investigated hospital service use to provide a better understanding of the collective health and economic impacts of rare diseases. METHODS: Novel methodology was developed using a carefully constructed set of diagnostic codes, a selection of rare disease cohorts from hospital administrative data, and advanced data-linkage technologies. Outcomes included health-service use and hospital admission costs. RESULTS: In 2010, cohort members who were alive represented approximately 2.0% of the Western Australian population. The cohort accounted for 4.6% of people discharged from hospital and 9.9% of hospital discharges, and it had a greater average length of stay than the general population. The total cost of hospital discharges for the cohort represented 10.5% of 2010 state inpatient hospital costs. CONCLUSIONS: This population-based cohort study provides strong new evidence of a marked disparity between the proportion of the population with rare diseases and their combined health-system costs. The methodology will inform future rare-disease studies, and the evidence will guide government strategies for managing the service needs of people living with rare diseases.Genet Med advance online publication 22 September 2016.

The Western Australian family connections genealogical project: detection of familial occurrences of single gene and chromosomal disorders.

AIM: To investigate using a Western Australian (WA) genealogical database for the identification of single gene and chromosome disorders among families. METHOD: Hospital admissions for single gene and chromosome disorders recorded during 2000-2006 were identified from the WA Hospital Morbidity Data System. The proportion of these conditions occurring in family groups was then identified using genealogical links created through the WA Family Connections Genealogical Project. RESULTS: There were 216 family clusters among 11,303 people who were recorded as having a genetic or chromosomal disorder on their hospital admission record. The most common single gene conditions found to occur in multiple family members included blood clotting disorders such as Factor VIII deficiency and Von Willebrand's disease, followed by cystic fibrosis, myotonic dystrophies, neurofibromatosis, tuberous sclerosis, and osteogenesis imperfecta. DISCUSSION: Single gene disorders most commonly occurring in multiple family members have been identified using the WA Family Connections Genealogical Project. These disorders reflect the most common single gene disorders requiring hospital admission, but which are not fatal before reproductive age and do not result in a loss of fertility. They are also restricted to disorders with earlier onset, as the WA Family Connections Genealogical Project currently covers 2-3 of the most recent generations. This study demonstrates the utility of record linkage genealogies to identify kindred with genetic disorders, offering a rich resource of information for focused genetic epidemiological research.

Baseline investigations of folate status in Aboriginal and non-Aboriginal West Australians prior to the introduction of mandatory fortification.

OBJECTIVE: In September 2009, Australia implemented mandatory folic acid fortification of wheat flour for bread-making to reduce the incidence of neural tube defects. Our study aimed to establish baseline folate status data in Aboriginal and non-Aboriginal Western Australians. METHODS: Patients who presented at a health service or collection centre for blood tests were invited to participate. One hundred and ninety-one Aboriginals and 159 non-Aboriginals were recruited between April 2008 and September 2009. Participants completed a five-minute questionnaire and had blood taken for red blood cell (RBC) folate and serum vitamin B12. Data were analysed using SPSS (version 17.0.2, SPSS Inc., Chicago, IL, USA). RESULTS: Ten per cent (95% confidence intervals (CI): 5, 19) of the Aboriginal women participants and 26% (95% CI: 16, 40) of men had RBC folate concentrations below 250 ng/mL, the cut-off associated with folate deficiency. None of the non-Aboriginal women (95% CI: 0, 4) and 4% of the non-Aboriginal men (95% CI: 2, 12) had RBC folate concentrations below 250 ng/mL. All participants were vitamin B12 replete. None of the 96 Aboriginal and 8% of non-Aboriginal women aged 16-44 reported consumption of supplements with a daily intake of >400 µg folic acid during the previous week. CONCLUSIONS AND IMPLICATIONS: This study established a baseline of RBC folate, folate consumption and supplement use in Aboriginal and non-Aboriginal groups. We identified 10% of Aboriginal women and none of non-Aboriginal women participants with low folate concentrations. The higher prevalence of folate deficiency in Aboriginal participants suggests they are more likely to benefit from a universal program of folate fortification.

The impact of single gene and chromosomal disorders on hospital admissions in an adult population.

Although the role of single gene and chromosomal disorders in pediatric illness has been recognized since the 1970s, there are few data describing the impact of these often severe disorders on the health of the adult population. In this study, we present population data describing the impact of single gene and chromosomal disorders on hospital admissions of patients aged 20 years and over in Western Australia between 2000 and 2006. The number, length, and cost of admissions were investigated and compared between disease categories and age groups and to hospital admissions for any reason. In total, 73,211 admissions and 8,032 patients were included in the study. The most costly disorders were cystic kidney disease, α-1 anti-trypsin deficiency, hemochromatosis, von Willebrand disease, and cystic fibrosis. Overall, patients with single gene and chromosomal disorders represented 0.5% of the patient population and were responsible for 1.9% of admissions and 1.5% of hospital costs. These data will enable informed provision of health care services for adults with single gene and chromosomal disorders in Australia.

Compliance with professional guidelines with reference to familial cancer services.

OBJECTIVE: Professional guidelines define the risk categorisation of patients for a genetic predisposition to cancer based on family history. These guidelines inform the appropriate referral of patients to specialist familial cancer services. Our study aimed to determine the quality of referral letters from general practitioners and specialists to genetic services for breast, ovarian and colorectal cancers, and their compliance with relevant professional guidelines. METHODS: A retrospective review of the referral letters and patient files of 241 consecutive patients referred between June and October 2008. RESULTS: Sufficient information to make a risk assessment was provided in 71% of referrals. Of these, 89% were compliant with guidelines. Genetic counsellors collected further information on 167 of the 241 referred patients and of these 83% were appropriate for referral according to guidelines. CONCLUSIONS AND IMPLICATIONS: Overall, referrals to familial cancer genetic services complied with professional referral guidelines. The majority of referrals were high quality, and with additional information, most patients were shown to be appropriate for review in a familial cancer clinic. Despite this, a better understanding of the reasons for non compliant referrals, and appropriate targeted education and resources is recommended to improve referral quality and compliance.

Socio-demographic disparities in the uptake of prenatal screening and diagnosis in Western Australia.

INTRODUCTION: Since the early 1980s, prenatal screening using ultrasound and biochemical markers has been used to refine the risk of Down syndrome and other fetal anomalies prior to considering fetal karyotyping. The performance of prenatal screening is subject to ongoing monitoring in Western Australia. The collection of these data can also assist in the identification of any potential inequities of access to prenatal screening within the state-wide programme. METHODS: Prenatal screening data (2005-2006) were collected from accredited ultrasound and pathology laboratories in Western Australia. Screening data were linked to diagnostic and pregnancy outcome data. Performance characteristics of screening and uptake by socio-demographic characteristics were analysed. RESULTS: Complete screening data were collected for 35,142 of the estimated 38,081 women screened during 2005 and 2006. There were 59,999 births related to this screening period. The lowest uptake of screening was among women who were Aboriginal (14.9%), living in remote areas (38.0%), under the age of 25 (40.2%), in the lowest quintile of the SEIFA index (41.6%) and with three or more children (48.4%). Logistic regression analysis showed all socio-demographic factors to be strongly associated with screening behaviour, with adjustment for ethnicity, socio-economic status, age, parity and area of residence. DISCUSSION: Our results have important implications for the delivery of prenatal screening services in Western Australia. While the screening programme meets international and national performance standards, the disparities in screening uptake suggest inequity in access to services, particularly for Aboriginal, remote and socio-economically disadvantaged women.

Informing policy for the Australian context - Costs, outcomes and cost savings of prenatal carrier screening for cystic fibrosis.

AIMS: To examine the costs, outcomes and cost savings of three models of prenatal cystic fibrosis (CF) carrier screening compared to no screening from a public health sector perspective. METHODS: A decision tree was generated to estimate costs and outcomes for each screening model for a hypothetical cohort of 38 000 pregnancies. Sensitivity analysis assessed the impact of model parameter variation. RESULTS: Under baseline assumptions, the initial annual cost to provide a prenatal CF carrier-screening programme is Au$5.32 million, Au$3.35 million and $2.93 million for one-step, two-step simultaneous and two-step sequential screening respectively. Annual costs are significantly lower for an established programme. No screening model provides a net saving over a lifetime horizon; however, the results were sensitive to variation in lifetime cost of care, screening test costs and number of pregnancies per carrier couple. CONCLUSIONS: Under some scenarios, prenatal CF carrier screening is cost saving to the health system; however, this is not conclusive and depends on several factors. Cost remains a potential barrier due to the substantial level of funding required in the short term. Feasibility and psychosocial, ethical and legal implications of screening need to be considered. Additionally, consultation is required with the Australian community on the acceptability and/or desire for prenatal CF carrier screening.

Combining first and second trimester markers for Down syndrome screening: think twice.

AIMS: This study compares different screening strategies for the detection of Down syndrome and considers practical implications of using multiple screening protocols. METHODS: The performance characteristics of each screening strategy were assessed based on datasets of Down syndrome (n=11) and unaffected pregnancies (n=1006) tested in both first and second trimester, as well as data from first trimester (n=18,901) and second trimester (n=40,748) pregnancies. RESULTS: For a detection rate of 91%, the false positive rates for integrated and serum integrated screening were 2.5% and 6.3%, respectively, compared with combined first trimester (4.6%) and second trimester (12.6%) screening. Contingent and sequential screening protocols achieved detection rates of 82 to 91% with false positive rates between 2.6 and 2.9%. Contingent protocols require retesting of 15 to 20% of cases in the second trimester. Sequential and integrated protocols require retesting of 98 to 100% of cases in the second trimester. The various screening strategies did not always detect the same Down syndrome pregnancies. CONCLUSIONS: Combining first and second trimester markers for Down syndrome screening better defines the at-risk population. However, integrated protocols complicate management of screening programs and may not be suitable as primary screening strategies. It may be a better use of resources to refine current first and second trimester programs through improved access and new markers. We therefore suggest thinking twice before embracing integrated population screening programs.

First trimester predictors of adverse pregnancy outcomes.

AIM: To identify first trimester indicators of adverse pregnancy outcomes. METHOD: Data were obtained from the statewide evaluation of first trimester screening for Down syndrome in Western Australia which included 22,695 pregnancies screened between August 2001 and October 2003. Screening data were linked with pregnancy outcome information from the Hospital Morbidity Database and the Birth Defects Registry. The odds ratios (OR) of adverse outcomes were analysed for combined risk incorporating maternal age, nuchal translucency (NT) and biochemical parameters and then separately for each parameter (pregnancy-associated plasma protein-A (PAPP-A), free beta human chorionic gonadotropin (beta-hCG) and NT). RESULTS: Risk assessments for first trimester combined screening are derived from maternal age, ultrasound measurement of fetal NT, maternal serum free beta-hCG and PAPP-A. Increased combined risk for Down syndrome was significantly (P < 0.01) associated with spontaneous loss at or before 24 weeks gestation (OR 13.51), birth defects (OR 6.58) and preterm birth at or before 32 weeks gestation (OR 3.2). Maternal serum PAPP-A below the 5th centile was associated with Down syndrome (OR 8.43), spontaneous loss before 24 weeks (OR 5.04) and later than 24 weeks (OR 4.50), preterm delivery before 32 weeks (OR 3.11) and before 37 weeks (OR 2.24). NT above the 95th centile was associated with Down syndrome (OR 43.91), birth defects (OR 4.02) and spontaneous loss before 24 weeks (OR 6.24). Low levels of free beta-hCG and increased NT were less consistently associated with adverse outcomes and high levels of free beta-hCG showed limited use as an indicator. The detection rates for all outcomes other than Down syndrome were less than 40%. CONCLUSION: Biochemical indicators and NT that are measured during first trimester screening for Down syndrome show a number of associations with adverse outcomes, but do not show appropriate performance characteristics for screening tests. These data are consistent with the view that the individual components, specifically low PAPP-A levels alone, do not provide an effective screening tool for adverse pregnancy outcomes.

Repeat adverse drug reactions causing hospitalization in older Australians: a population-based longitudinal study 1980-2003.

AIM: To examine trends in the rate of repeat adverse drug reactions (ADRs) causing hospitalization in older Australians and to identify the most common ADRs and drugs most often implicated in repeat and first-time ADRs. METHODS: Analysis of routinely collected hospital record administrative data, with International Classification of Diseases external cause codes for ADRs extracted from the Western Australia (WA) Hospital Morbidity Data System and WA Death Register, for people aged > or =60 years in 1980-2003. RESULTS: A total of 37 296 people aged > or =60 years with an ADR-related hospitalization were identified. Among them, 6853 (18.4%) patients had 10 212 repeat ADRs. Repeat ADRs consistently increased from 1980 and reached 30.3% of all ADRs by 2003. The mean time interval declined with each successive repeat ADR (810, 606 and 299 days for the first, second and higher ranked repeat episodes, respectively). The most common repeat ADRs were nausea/vomiting (8.0%), haemorrhage due to anticoagulants (5.5%), drug-induced osteoporosis (4.8%) and poisoning by cardiovascular agents (3.9%). The drugs most often involved in repeat ADRs were cardiovascular agents (15.6%), antineoplastic drugs (11.0%), corticoids (10.1%), anticoagulants (8.6%), antirheumatics/nonsteroidal anti-inflammatory drugs (5.1%) and opioids (4.9%). The trends of anticoagulants and antineoplastic drugs implicated in repeat ADRs were still rising at the end of the study. The specific drug classes involved in repeat ADRs differed in relative importance from first-time ADRs. CONCLUSIONS: Repeat ADR-related hospitalizations have consistently increased in elderly Australians from 1980 to 2003. Strategies to ensure the safer use of medicines, in particular anticoagulants, in this population are warranted.

Length of comorbidity lookback period affected regression model performance of administrative health data.

BACKGROUND AND OBJECTIVE: The impact of different comorbidity ascertainment lookback periods on modeling posthospitalization mortality and readmission was examined. METHODS: Index cases comprised medical (n = 326,456) and procedural (n = 349,686) patients with a hospital admission from 1990-1996. Administrative hospital data were extracted for 102 comorbidities, ascertained at index admission and for 1-, 2-, 3-, and 5-year lookback periods. Deaths and readmissions were identified within 12 months and 30 days of separation, respectively. Hierarchically nested and nonnested Cox regressions as well as Receiver Operator Characteristic Area Under the Curve (ROC-AUC) were used to determine model-fit and predictive ability of lookback period models. RESULTS: The 1-year lookback period provided the best model-fit for both patient groups when modeling mortality. A similar model-fit was seen at index admission for procedural but not medical patients. The superior readmission model employed 5 years of lookback for both patient groups. With one exception, all lookback period models were superior to those abstracting comorbidity from index admission only. Similar results were evident from ROC-AUC, although greater predictive ability was seen with modeling of mortality (0.847-0.923) compared with readmission (0.593-0.681). CONCLUSION: The explanatory power of regression models, when adjusting for comorbidity, is influenced by length of lookback, outcome investigated and clinical subgroup. Shorter periods (approximately 1 year) appear appropriate for modeling posthospitalization mortality, whereas longer lookback periods are superior for readmission outcomes.