BackgroundDexamethasone is important in the treatment for pediatric acute lymphoblastic leukemia (ALL) but induces muscle atrophy with negative consequences for muscle mass, muscle strength, and... Show moreBackgroundDexamethasone is important in the treatment for pediatric acute lymphoblastic leukemia (ALL) but induces muscle atrophy with negative consequences for muscle mass, muscle strength, and functional abilities. The aim of this study was to establish the effect of a dexamethasone course on sarcopenia and physical frailty in children with ALL, and to explore prognostic factors.MethodsPatients with ALL aged 3-18 years were included during maintenance therapy. Patients had a sarcopenia/frailty assessment on the first day of (T1) and on the day after (T2) a 5-day dexamethasone course. Sarcopenia was defined as low muscle strength in combination with low muscle mass. Prefrailty and frailty were defined as having two or >= three of the following components, respectively: low muscle mass, low muscle strength, fatigue, slow walking speed, and low physical activity. Chi-squared and paired t-tests were used to assess differences between T1 and T2. Logistic regression models were estimated to explore patient- and therapy-related prognostic factors for frailty on T2.ResultsWe included 105 patients, 61% were boys. Median age was 5.3 years (range: 3-18.8). At T1, sarcopenia, prefrailty, and frailty were observed in respectively 2.8%, 23.5%, and 4.2% of patients. At T2, the amount of patients with frailty had increased to 17.7% (p = 0.002), whereas the number of patients with sarcopenia and prefrailty remained similar. Higher ASMM (odds ratio [OR]: 0.49, 95% CI: 0.28-0.83), stronger handgrip strength (OR: 0.41, 95% CI: 0.22-0.77) and more physical activity minutes per day (OR: 0.98, 95% CI: 0.96-0.99) decreased the risk of frailty at T2. Slower walking performance (OR: 2, 95% CI: 1.2-3.39) increased the risk. Fatigue levels at T1 were not associated with frailty at T2.ConclusionPhysical frailty increased strikingly after a 5-days dexamethasone course in children with ALL. Children with poor physical state at start of the dexamethasone course were more likely to be frail after the course.Dexamethasone is important in the treatment for pediatric acute lymphoblastic leukemia (ALL) but induces muscle atrophy. After a 5-day dexamethasone course. Physical frailty increased with 13.5% in pediatric ALL patients. A poorer physical state at start of a dexamethasone course (lower muscle mass, muscle strength, or slower movement ability) was prognostic for developing frailty after a dexamethasone course.image Show less
ObjectivesDelirium is a serious condition, which poses treatment challenges during hospitalisation for COVID-19. Improvements in testing, vaccination and treatment might have changed patient... Show moreObjectivesDelirium is a serious condition, which poses treatment challenges during hospitalisation for COVID-19. Improvements in testing, vaccination and treatment might have changed patient characteristics and outcomes through the pandemic. We evaluated whether the prevalence and risk factors for delirium, and the association of delirium with in-hospital mortality changed through the pandemic.MethodsThis study was part of the COVID-OLD study in 19 Dutch hospitals including patients ≥70 years in the first (spring 2020), second (autumn 2020) and third wave (autumn 2021). Multivariable logistic regression models were used to study risk factors for delirium, and in-hospital mortality. Differences in effect sizes between waves were studied by including interaction terms between wave and risk factor in logistic regression models.Results1540, 884 and 370 patients were included in the first, second and third wave, respectively. Prevalence of delirium in the third wave (12.7%) was significantly lower compared to the first (22.5%) and second wave (23.5%). In multivariable-adjusted analyses, pre-existing memory problems was a consistent risk factor for delirium across waves. Previous delirium was a risk factor for delirium in the first wave (OR 4.02), but not in the second (OR 1.61) and third wave (OR 2.59, p-value interaction-term 0.028). In multivariable-adjusted analyses, delirium was not associated with in-hospital mortality in all waves.ConclusionDelirium prevalence declined in the third wave, which might be the result of vaccination and improved treatment strategies. Risk factors for delirium remained consistent across waves, although some attenuation was seen in the second wave. Show less
Frailty is increasingly recognized as an important concept in patients with Inflammatory Bowel Disease (IBD). The aim of this scoping review is to summarize the current literature on frailty in IBD... Show moreFrailty is increasingly recognized as an important concept in patients with Inflammatory Bowel Disease (IBD). The aim of this scoping review is to summarize the current literature on frailty in IBD. We will discuss the definition of frailty, frailty assessment methods, the prevalence of frailty, risk factors for frailty and the prognostic value of frailty in IBD. A scoping literature search was performed using the PubMed database. Frailty prevalence varied from 6% to 53.9%, depending on the population and frailty assessment method. Frailty was associated with a range of adverse outcomes, including an increased risk for all-cause hospitalization and readmission, mortality in non-surgical setting, IBD-related hospitalization and readmission. Therefore, frailty assessment should become integrated as part of routine clinical care for older patients with IBD. Show less
Objectives: While randomized controlled trials have proven the benefits of blood pressure (BP) lowering in participating octogenarians, population-based observational studies suggest an association... Show moreObjectives: While randomized controlled trials have proven the benefits of blood pressure (BP) lowering in participating octogenarians, population-based observational studies suggest an association between low systolic blood pressure (SBP) and faster overall decline. This study investigates the effects of BP-lowering treatment, a history of cardiovascular diseases (CVD), and cognitive and physical fitness on the associations between SBP and health outcomes in the very old. Methods: Five cohorts from the Towards Understanding Longitudinal International older People Studies (TULIPS) consortium were included in a two-step individual participant data meta-analysis (IPDMA). We pooled hazard ratios (HR) from Cox proportional-hazards models for 5-year mortality and estimates of linear mixed models for change in cognitive and functional decline. Models were stratified by BP-lowering treatment, history of CVD, Mini-Mental State Examination scores, grip strength (GS) and body mass index (BMI). Results: Of all 2480 participants (59.9% females, median 85 years), median baseline SBP was 149 mmHg, 64.3% used BP-lowering drugs and 47.3% had a history of CVD. Overall, higher SBP was associated with lower all-cause mortality (pooled HR 0.91 [95% confidence interval 0.88-0.95] per 10 mmHg). Associations remained irrespective of BP-lowering treatment, history of CVD and BMI, but were absent in octogenarians with above-median MMSE and GS. In pooled cohorts, SBP was not associated with cognitive and functional decline. Conclusion: While in the very old with low cognitive or physical fitness a higher SBP was associated with a lower all-cause mortality, this association was not evident in fit octogenarians. SBP was not consistently associated with cognitive and functional decline. Show less
Wubben, N.; Haaksma, M.; Ramakers, I.H.G.B.; Flier, W.M. van der; Verhey, F.R.J.; Rikkert, M.G.M.O.; Melis, R.J.F. 2022
Objectives: To explain the heterogeneity in dementia disease trajectory, we studied the influence of changing patient characteristics on disease course by comparing the association of dementia... Show moreObjectives: To explain the heterogeneity in dementia disease trajectory, we studied the influence of changing patient characteristics on disease course by comparing the association of dementia progression with baseline comorbidity and frailty, and with time-varying comorbidity and frailty.Methods: We used individual growth models to study baseline and time-varying associations in newly diagnosed dementia patients (n = 331) followed for 3 years. We measured cognition using the Mini-Mental State Examination (MMSE), daily functioning using the Disability Assessment for Dementia (DAD), frailty using the Fried criteria and comorbidity using the Cumulative Illness Rating Scale for Geriatrics (CIRS-G).Results: Although baseline comorbidity and frailty were associated with decreased daily functioning at diagnosis, their effects clearly diminished over time. In contrast, when incorporating comorbidity and frailty as time-varying covariates, comorbidity was associated with lower daily functioning, and frailty with both lower cognition and daily functioning. Being frail was associated with a 0.9-point lower MMSE score (p = 0.03) and a 14.9-point lower DAD score (p < 0.01). A 1-point increase in CIRS-G score was associated with a 1.1-point lower DAD score (p < 0.01).Conclusions: Time-varying comorbidity and frailty were more consistently associated with dementia disease course than baseline comorbidity and frailty. Therefore, modeling only baseline predictors is insufficient for understanding the course of dementia in a changing patient context. Show less
Bruijnen, C.P.; Koldenhof, J.J.; Verheijden, R.J.; Bos, F. van den; Emmelot-Vonk, M.H.; Witteveen, P.O.; Suijkerbuijk, K.P.M. 2022
Background: Immune checkpoint inhibitors (ICIs) can cause immune-related adverse events (irAEs) that range from mild to life-threatening. Age itself does not seem to be a predictor for the... Show moreBackground: Immune checkpoint inhibitors (ICIs) can cause immune-related adverse events (irAEs) that range from mild to life-threatening. Age itself does not seem to be a predictor for the occurrence of irAEs. It is unknown whether frailty plays a role in the occurrence of irAEs. Therefore, the authors assessed whether irAEs and their sequelae occur more often in frail patients than in fit patients according to the Geriatric 8 (G8) assessment. Methods: Patients with melanoma aged 70 years and older who were about to start ICI therapy and were screened with the G8 assessment were enrolled in this prospective, observational study. Patients were classified by the G8 as either fit or frail. The primary outcome was the occurrence of grade >= 3 irAEs. Results: In total, 92 patients were included for statistical analyses, 26 (29%) of whom were classified as frail. Grade >= 3 irAEs occurred in 20% of patients. There was no significant difference in the occurrence of grade >= 3 irAEs between fit and frail patients (17% vs 27%; P = .26). Frail patients were admitted to the hospital because of irAEs significantly more often than fit patients (29% vs 54%; P = .02) and showed a trend toward increased length of hospitalization (5 vs 8 days; P = .06) and more frequent use of immunosuppressants or ICI discontinuation for irAEs (36% vs 58%; P = .06). Conclusions: Although frailty appears to be unrelated to the occurrence of severe irAEs, it is an indicator of irAE-related adverse sequelae, such as hospital admission. Screening for frailty can be of added value in the shared decision-making process for older patients who qualify for ICI treatment. Show less
Gordon, A.L.; Achterberg, W.P.; Delden, J.J.M. van 2022
The COVID-19 pandemic has particularly adversely affected older people with frailty and functional dependency. Essential regular contact with care staff has been evidenced as an important source of... Show moreThe COVID-19 pandemic has particularly adversely affected older people with frailty and functional dependency. Essential regular contact with care staff has been evidenced as an important source of infection for this group. Vaccinating care staff can reduce the incidence, duration and severity of infection, preventing onward transmission to older people and minimising the harm associated with discontinuity caused by staff absence. Voluntary vaccination programmes for staff are more likely to be effective when associated with information and education, community engagement and financial incentives, but programmes using all of these approaches have failed to establish consistently high vaccination rates among care staff during the pandemic. Mandatory vaccination, proposed as a solution in some countries, can increase vaccination rates. It is only ethical if a vaccine is effective and cost-effective, the risk associated with vaccinating care workers is proportionate to the risk reduction achieved through vaccination, and where all efforts to encourage voluntary vaccination have been exhausted. Even when these conditions have been met, careful attention is required to ensure that the penalties associated with conscientious objection are proportionate and to ensure that implementation is equitable in a way that does not disadvantage particular groups of staff. Show less
Background as the coronavirus disease of 2019 (COVID-19) pandemic progressed diagnostics and treatment changed. Objective to investigate differences in characteristics, disease presentation and... Show moreBackground as the coronavirus disease of 2019 (COVID-19) pandemic progressed diagnostics and treatment changed. Objective to investigate differences in characteristics, disease presentation and outcomes of older hospitalised COVID-19 patients between the first and second pandemic wave in The Netherlands. Methods this was a multicentre retrospective cohort study in 16 hospitals in The Netherlands including patients aged >= 70 years, hospitalised for COVID-19 in Spring 2020 (first wave) and Autumn 2020 (second wave). Data included Charlson comorbidity index (CCI), disease severity and Clinical Frailty Scale (CFS). Main outcome was in-hospital mortality. Results a total of 1,376 patients in the first wave (median age 78 years, 60% male) and 946 patients in the second wave (median age 79 years, 61% male) were included. There was no relevant difference in presence of comorbidity (median CCI 2) or frailty (median CFS 4). Patients in the second wave were admitted earlier in the disease course (median 6 versus 7 symptomatic days; P < 0.001). In-hospital mortality was lower in the second wave (38.1% first wave versus 27.0% second wave; P < 0.001). Mortality risk was 40% lower in the second wave compared with the first wave (95% confidence interval: 28-51%) after adjustment for differences in patient characteristics, comorbidity, symptomatic days until admission, disease severity and frailty. Conclusions compared with older patients hospitalised in the first COVID-19 wave, patients in the second wave had lower in-hospital mortality, independent of risk factors for mortality. The better prognosis likely reflects earlier diagnosis, the effect of improvement in treatment and is relevant for future guidelines and treatment decisions. Show less
As the world's population continues to age over the decades ahead, medical educators and researchers in every adult medical and surgical specialty will need to 'geriatricise' their clinical science... Show moreAs the world's population continues to age over the decades ahead, medical educators and researchers in every adult medical and surgical specialty will need to 'geriatricise' their clinical science. Many have already engaged with geriatrics. Here we describe the progress that has been made and the opportunities ahead in the field of Geriatric Emergency Medicine (GEM), a field that has taken large steps in integrating holistic care. Future opportunities exist in the three domains of evidence-based medicine: including patient preferences and needs, generating scientific evidence, and improving physician knowledge and expertise. Implementation requires new innovations also in the organisation of care. Similar strategies may be useful in other fields of medicine, in making holistic care the standard for older people. Show less
Optimizing emergency care for the aging population is an important future challenge, as the proportion of older patients at the emergency department (ED) rapidly increases. Older patients,... Show moreOptimizing emergency care for the aging population is an important future challenge, as the proportion of older patients at the emergency department (ED) rapidly increases. Older patients, particularly those who are frail, have a high risk of adverse outcomes after an ED visit, such as functional decline, institutionalization, and death. The ED can have a key position in identifying frail older patients who benefit most from comprehensive geriatric care [including delirium preventive measures, early evaluation of after-discharge care, and a comprehensive geriatric assessment (CGA)]. However, performing extensive frailty assessment is not suitable at the ED. Therefore, quick and easy-to-use instruments are needed to identify older patients at risk for adverse outcomes. This narrative review outlines the importance and complexity of frailty assessment at the ED. It aligns the available screening instruments, including clinical judgment as frailty assessment, and summarizes arguments for and against frailty assessment at the ED. Show less
Simple Summary The objective was to develop and internally validate a predictive model based on preoperative predictors, including geriatric characteristics, for severe postoperative complications... Show moreSimple Summary The objective was to develop and internally validate a predictive model based on preoperative predictors, including geriatric characteristics, for severe postoperative complications after elective surgery for stage I-III CRC in patients >= 70 years. Potential predictors included demographics, comorbidity, tumour location, activities of daily living (ADL), history of falls, malnutrition, risk factors for delirium, use of mobility aid and polypharmacy. The least absolute shrinkage and selection operator (LASSO) method was used for predictor selection and prediction model building. A geriatric model that included gender, previous DVT or pulmonary embolism, COPD/asthma/emphysema, rectal cancer, the use of a mobility aid, ADL assistance, previous delirium and polypharmacy showed satisfactory discrimination with an AUC of 0.69 (95% CI 0.73-0.64); the AUC for the optimism corrected model was 0.65. An eight-item colorectal geriatric model (GerCRC) was developed. After external validation, this risk model has the potential to be used for preoperative (shared) decision-making. Introduction Older patients have an increased risk of morbidity and mortality after colorectal cancer (CRC) surgery. Existing CRC surgical prediction models have not incorporated geriatric predictors, limiting applicability for preoperative decision-making. The objective was to develop and internally validate a predictive model based on preoperative predictors, including geriatric characteristics, for severe postoperative complications after elective surgery for stage I-III CRC in patients >= 70 years. Patients and Methods: A prospectively collected database contained 1088 consecutive patients from five Dutch hospitals (2014-2017) with 171 severe complications (16%). The least absolute shrinkage and selection operator (LASSO) method was used for predictor selection and prediction model building. Internal validation was done using bootstrapping. Results: A geriatric model that included gender, previous DVT or pulmonary embolism, COPD/asthma/emphysema, rectal cancer, the use of a mobility aid, ADL assistance, previous delirium and polypharmacy showed satisfactory discrimination with an AUC of 0.69 (95% CI 0.73-0.64); the AUC for the optimism corrected model was 0.65. Based on these predictors, the eight-item colorectal geriatric model (GerCRC) was developed. Conclusion: The GerCRC is the first prediction model specifically developed for older patients expected to undergo CRC surgery. Combining tumour- and patient-specific predictors, including geriatric predictors, improves outcome prediction in the heterogeneous older population. Show less
Warmerdam, B.W.C.M.; Holstein, Y. van; Eefting, D.; Rijswijk, C.S.P. van; Meer, R.W. van der; Mooijaart, S.P.; ... ; Schaik, J. van 2021
Purpose Complex endovascular aortic repair (EVAR) procedures provide a treatment option for patients with aortic aneurysms involving visceral branches. Good technical results and short-term... Show morePurpose Complex endovascular aortic repair (EVAR) procedures provide a treatment option for patients with aortic aneurysms involving visceral branches. Good technical results and short-term outcomes have been reported. Whether complex EVAR provides acceptable functional outcomes is not clear. The current study aims to describe postoperative functional outcomes in complex EVAR patients-an older and relatively frail patient group. Materials and Methods A single-center retrospective cohort study was performed, using data from a computerized database of consecutive patients who underwent complex EVAR in the Leiden University Medical Center (LUMC, The Netherlands) between July 2013 and September 2020. As of May 2017, patients scheduled for complex EVAR were referred to a geriatric care pathway to determine (Instrumental) Activities of Daily Living ((I)ADL) scores at baseline and, if informed consent was given, after 12 months. For the total patient group, adverse functional performance outcomes were: discharge to a nursing home and 12-month mortality. For the patients included in geriatric follow-up, the additional outcome was the incidence of functional decline (defined by a >= 2 point increase in (I)ADL-score) at 12-month follow-up Results Eighty-two patients underwent complex EVAR, of which 68 (82.9%) were male. Mean age was 73.3 years (SD=6.3). Within 30 days postsurgery, 6 patients (7.3%) died. Mortality within 12 months for the total patient group was 14.6% (n=12). After surgery, no patients had to be discharged to a nursing home. Fifteen patients (18.3%) were discharged to a rehabilitation center. Twenty-three patients gave informed consent and were included in geriatric follow-up. Five patients (21.7%) presented functional decline 12 months postsurgery and 4 patients had died (17.4%) by that time. This means that 39.1% of the patients in the care pathway suffered an adverse outcome. Conclusion To our knowledge, this is the only study that examined functional performance after complex EVAR, using a prospectively maintained database. No patients were newly discharged to a nursing home and functional performance results at 12 months are promising. Future multidisciplinary research should focus on determining which patients are most prone to deterioration of function, so that efforts can be directed toward preventing postoperative functional decline. Show less
Bohnstedt, M.; Putter, H.; Danko, A.; Danko, M.J.; Gampe, J. 2021
When a recurrent event process is ended by death, this may imply dependent censoring if the two processes are associated. Such dependent censoring would have to be modeled to obtain a valid... Show moreWhen a recurrent event process is ended by death, this may imply dependent censoring if the two processes are associated. Such dependent censoring would have to be modeled to obtain a valid inference. Moreover, the dependence between the recurrence process and the terminal event may be the primary topic of interest. Joint frailty models for recurrent events and death, which include a separate dependence parameter, have been proposed for exactly observed recurrence times. However, in many situations, only the number of events experienced during consecutive time intervals are available. We propose a method for estimating a joint frailty model based on such interval counts and observed or independently censored terminal events. The baseline rates of the two processes are modeled by piecewise constant functions, and Gaussian quadrature is used to approximate the marginal likelihood. Covariates can be included in a proportional rates setting. The observation intervals for the recurrent event counts can differ between individuals. Furthermore, we adapt a score test for the association between recurrent events and death to the setting in which only individual interval counts are observed. We study the performance of both approaches via simulation studies, and exemplify the methodology in a biodemographic study of the dependence between budding rates and mortality in the species Eleutheria dichotoma. Show less
Vlies, E. van der; M. los; Stijns, P.E.F.; Hengel, M. van; Blaauw, N.M.S.; Bos, W.J.W.; ... ; Noordzij, P.G. 2020
Objective To determine the value of preoperative frailty screening in predicting postoperative severe complications and 1-year mortality in patients undergoing radical cystectomy (RC). Patients and... Show moreObjective To determine the value of preoperative frailty screening in predicting postoperative severe complications and 1-year mortality in patients undergoing radical cystectomy (RC). Patients and Methods Prospective cohort single-centre study in patients undergoing RC from September 2016 to December 2017. Preoperative frailty screening was implemented as standard care and was used to guide shared decision-making during multidisciplinary team meetings. Frailty screening consisted of validated tools to assess physical, mental and social frailty. Patients were considered frail when having two or more frailty characteristics. The primary endpoint was the composite of a severe complication (Clavien-Dindo Grade III-V) within 30 days and 1-year all-cause mortality. The secondary endpoints included any complication (Clavien-Dindo II-V), length of stay, readmission within 30 days, and all-cause mortality. Logistic regression analysis and the concordance statistic (c-statistic) were used to describe the association and predictive value of preoperative frailty screening. Results A total of 63 patients were included; 39 (61.9%) were considered frail. Preoperative frailty was associated with a seven-fold increased risk of a severe complication or death 1 year after RC [adjusted odds ratio (OR) 7.36, 95% confidence interval (CI) 1.7-31.8; 22 patients]. Compared to the American Society of Anesthesiologists (ASA) score and Charlson Comorbidity Index, frailty showed the best model performance (NagelkerkeR(2)0.20) and discriminative ability(c-statistic 0.72,P < 0.01) for the primary endpoint. After adding frailty to the conventional ASA risk score, the c-statistic improved by 11% (P < 0.01). Overall survival was significantly worse in frail patients (23.2 months, 95% CI 18.7-30.1) vs non-frail patients (32.9 months, 95% CI 30.0-35.9;P = 0.01). Conclusions Frail patients undergoing RC are at high risk of postoperative adverse outcomes including death. Preoperative frailty screening improves preoperative risk stratification and may be used to guide patient selection for RC. Show less
Objectives Older adults with psychiatric disorders have a substantially lower life expectancy than age-matched controls. Knowledge of risk factors may lead to targeting treatment and interventions... Show moreObjectives Older adults with psychiatric disorders have a substantially lower life expectancy than age-matched controls. Knowledge of risk factors may lead to targeting treatment and interventions to reduce this gap in life expectancy. In this study, we investigated whether frailty independently predicts mortality in older patients following an acute admission to a geriatric psychiatry hospital.Methods Clinical cohort study with a 5-year follow-up of 120 older patients admitted to a psychiatric hospital between February 2009 and September 2010. On admission, we assessed frailty with a frailty index (FI). We applied Cox regression analyses with time to death as the dependent variable, to examine whether the FI was a predictor for mortality, adjusted for age, sex, level of education, multimorbidity (Cumulative Illness Rating Scale for Geriatrics, CIRS-G scores), functional status (Barthel Index), neuropsychiatric symptoms (NPS), and severity of psychiatric symptoms at admission (Clinical Global Impressions Scale of Severity).Results Of the 120 patients, 63 (53%) patients were frail (FI >= 0.25), and 59 (49%) had died within 5 years. The FI predicted mortality with a hazard ratio (HR) of 1.78 (95% CI, 1.06-2.98) per 0.1 point increase, independent of the covariates. Co-morbidity measured by the CIRS-G and functional status measured by the Barthel Index were not significantly associated.Conclusions Frailty was a strong predictor of mortality, independent of age, gender, multimorbidity, and functional status. This implies that frailty may be helpful in targeting inpatient psychiatric treatment and aftercare according to patients' life expectancy. Show less
Geloven, N. van; Balan, T.A.; Putter, H.; Cessie, S. le 2020
We study the effect of delaying treatment in the presence of (unobserved) heterogeneity. In a homogeneous population and assuming a proportional treatment effect, a treatment delay period will... Show moreWe study the effect of delaying treatment in the presence of (unobserved) heterogeneity. In a homogeneous population and assuming a proportional treatment effect, a treatment delay period will result in notably lower cumulative recovery percentages. We show in theoretical scenarios using frailty models that if the population is heterogeneous, the effect of a delay period is much smaller. This can be explained by the selection process that is induced by the frailty. Patient groups that start treatment later have already undergone more selection. The marginal hazard ratio for the treatment will act differently in such a more homogeneous patient group. We further discuss modeling approaches for estimating the effect of treatment delay in the presence of heterogeneity, and compare their performance in a simulation study. The conventional Cox model that fails to account for heterogeneity overestimates the effect of treatment delay. Including interaction terms between treatment and starting time of treatment or between treatment and follow up time gave no improvement. Estimating a frailty term can improve the estimation, but is sensitive to misspecification of the frailty distribution. Therefore, multiple frailty distributions should be used and the results should be compared using the Akaike Information Criterion. Non-parametric estimation of the cumulative recovery percentages can be considered if the dataset contains sufficient long term follow up for each of the delay strategies. The methods are demonstrated on a motivating application evaluating the effect of delaying the start of treatment with assisted reproductive techniques on time-to-pregnancy in couples with unexplained subfertility. Show less
Eekelen, R. van; Putter, H.; McLernon, D.J.; Eijkemans, M.J.; Geloven, N. van 2019
