1. Contoh 1: Home Use of Paints and Petroleum Products and Risk of Childhood Leukemia Associations between childhood leukemia and parental occupational exposures to paints, solvents, and other petroleum products have been reported, however, little is known about the effect of these products when used at home. The role of home exposures to paints and petroleum products on the risk of childhood leukemia was evaluated in the Northern California Childhood Leukemia Study (NCCLS), an ongoing population-based case-control study. The current analyses include 382 incident leukemia cases (aged 0-14) enrolled from 1995-2002, and matched to 482 controls on age, sex, Hispanic status, and maternal race. A detailed history on home use of paints and petroleum products, time of exposure, and user was collected during an in home interview. Exposures were censored one year before diagnosis. Conditional logistic regression was performed adjusting for annual household income. An increased risk of childhood leukemia was observed with parental use of paints anytime pre- or postnatally (Odds Ratio (OR)=1.35, 95% Confidence Interval (CI)=0.99, 2.02), with a higher and significant risk when paints were used during both time periods (OR=1.72, 95% CI=1.07, 2.74). Maternal use of paints anytime pre- or postnatally conferred a significantly increased leukemia risk (OR=1.44, 95% CI=1.03, 2.02), while non- significant increased risks were detected for paternal use of paint anytime before or after birth. Exposures to paints by both parents after birth resulted in a two-fold significant increased risk (OR=1.97, 95%CI=1.18, 3.30). Subjects with acute lymphoblastic leukemia had greater risks compared to subjects with acute myeloblastic leukemia. No significant associations were seen with exposure to petroleum products across all time windows for either parent.

2. CONTOH 2: Association between body composition and blood pressure in a contemporary cohort of 9-year old children Background: Elevated blood pressure in children is an early risk factor for cardiovascular disease and is associated with body mass index (BMI). However as BMI does not distinguish between fat and lean, little is known about the relationship of blood pressure in children to different elements of body composition. Objective: This study aimed to investigate the association of blood pressure with total body fat, lean mass and trunk fat in a cohort of 9-year-old children. Design: Blood pressure, BMI and body composition were measured in 6, 863 children enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). Fat mass, lean mass and trunk fat were assessed using dual-energy X-ray absorptiometry (DXA). Results: Total body fat and BMI were strongly associated with systolic blood pressure (SBP) [β=3.50, 95%CI 3.27 to 3.74 mmHg/standard deviation (SD) and β=3.96, 95%CI 3.76 to 4.16 mmHg/SD, respectively] and weakly associated with diastolic blood pressure (DBP) (β=1.39, 95% CI 1.22 to 1.57 mmHg/SD and β=1.37, 95% CI 1.22 to 1.52 mmHg/SD, respectively). SBP was also positively associated with lean mass (β=3.60, 95% CI 3.22 to 3.97 mmHg/SD) and trunk fat (β=2.14, 95% CI 0.82 to 3.46 mmHg/SD, independent of total fat mass). Conclusion: Blood pressure in 9-year-old children is independently associated with fat mass and lean mass and, to a lesser extent, trunk fat. In this analysis, because both fat and lean mass are associated with blood pressure, BMI predicts blood pressure at least as well as these components of body composition.

3. Contoh 3: A Major Determinant of Recent Increases in HIV Incidence Among Men who Have Sex with Men (MSM) in British Columbia (BC): Deferred Initiation of Antiretroviral Therapy Background: Recent clinical guidelines endorse deferral of highly active antiretroviral therapy (HAART) until later in the course of HIV infection. The effect of this change on population levels of high viremia, infectivity and, in turn, sexual transmission of HIV is unknown. Objectives: Describe populational trends in HIV viremia among MSM in BC in relation to a 1999 change that deferred HAART from CD4 10 000 copies/mL) across 6-month intervals. Mathematical models predicted relative changes in infections among MSM following introduction and deferral of HAART. Results: The number and proportion of highly viremic MSM declined steadily [from 443 (27.6%)] for two years following introduction of HAART. This trend has reverted, increasing from 358 viremic MSM (17.8%) in the second half of 1999 to 713 (26.7%) at the end of 2003; the increase occurred among men with CD4 >200. Models predicted a 50% reduction in HIV diagnoses among MSM from 1997-1999 but rapid 83% increase following deferral of HAART. Conclusion: Deferral of therapy appears to be a major determinant of the 75% increase in annual HIV diagnoses among MSM in BC from 1999-2004. Substantial increases in HIV prevention among MSM seem warranted.

5. Me-Review CONTOH A: Bayesian propensity score analysis for observational data Propensity scores analysis (PSA) involves regression adjustment for the estimated propensity scores, and the method can be used for estimating causal effects from observational data. However, confidence intervals may be falsely precise because PSA ignores uncertainty in the estimated propensity scores. We propose Bayesian propensity score analysis (BPSA) for observational studies which involve a binary exposure, binary outcome and measured confounders. The method uses hierarchical modelling with the propensity score as a latent variable. The first level models the relationship between the outcome, exposure and propensity score, while the second level models the relationship between the propensity score and measured confounders. Markov chain Monte Carlo is used to study the posterior distribution of the exposure effect. Our objective is to implement BPSA using computer programs and investigate the performance of BPSA compared to PSA using Monte Carlo simulations. Synthetic datasets, of sample size n=250, 1000, 4000, were simulated by computer for various realistic parameter values. The datasets were analyzed using BPSA and PSA, and we estimated the coverage probability of 80% credible intervals. The estimated coverage probabilities ranged from 78% to 84% for BPSA, and from 42% to 82% for PSA, with simulation standard errors less than 2%. The simulation results indicate that BPSA provides improved inferences for exposure effects compared to PSA, in the sense that interval estimators have the correct frequentist coverage levels under repeated sampling of the data. We demonstrate BPSA in an observational study of the effect of statin therapy on all-cause mortality in patients discharged from hospital following acute myocardial infarction.

6. Review contoh b: Exposure to H. pylori-positive siblings and persistence of H. pylori infection in early childhood H.pylori infection is a common chronic infection, yet transmission pathways are unclear; evidence suggests that siblings play a role in transmission. Transient H.pylori infection is observed in children, but determinants of persistence are unknown. We examine the effect of exposure to H.pylori-positive siblings on the establishment of persistent H.pylori infection using data from the Pasitos Cohort Study, which recruited pregnant women from maternal-child clinics in El Paso, Texas, and Juarez, Mexico during 1998-2000 and followed 472 children after birth to identify predictors of H.pylori infection. Infection was detected at target intervals of 6 months in index children and younger siblings born during follow-up, using the 13C-urea breath test (UBT) corrected for variation in CO2 production. We used proportional hazards regression to estimate hazard ratios for the effect of having H.pylori-positive younger siblings on the rate of developing a persistent H.pylori infection in index children with 1+ younger siblings. Persistent infection was defined as 3 consecutive positive UBT results. We modeled two exposure definitions: infected younger sibling (1+ younger siblings with 1+ positive UBT results); persistently infected younger sibling (1+ younger siblings with a persistent infection). Adjusting for mom's education (the strongest H.pylori risk factor in this cohort), the hazard ratio was 4.0 (95% CI=1.8,8.2) for infected younger sibling and 9.3 (95% CI=3.2,26) for persistently infected younger sibling. Having H.pylori-positive younger siblings, particularly with persistent infection, was strongly associated with developing persistent H.pylori infection in this cohort.