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Medical Sciences	50%

Selected Abstracts

WHEN MISSING DATA ARE NOT MISSING: A NEW APPROACH TO EVALUATING SUPPLEMENTAL HOMICIDE REPORT IMPUTATION STRATEGIES,

CRIMINOLOGY, Issue 4 2008
TIM WADSWORTH
The Supplemental Homicide Reports (SHR) are widely used in criminological research and inform a broad range of research topics and subsequent policy applications. A serious issue with the SHR is missing information about the offender and incident in many recorded homicides. Although it is convenient to discard cases with missing data before analysis, such discarding is not theoretically justified and can lead to incorrect substantive conclusions. Recently, several techniques for imputing missing SHR data have been proposed, but it is difficult to evaluate their effectiveness. This research presents a new approach to testing and evaluating SHR imputation techniques. Offender data that are missing in the SHR are often found in police records available for individual cities. We examine similarities and differences among cases with known offender characteristics in the SHR, cases with such information missing in the SHR but available in police records, and cases with such information missing in both sources. We then use these data sets to evaluate four different imputation techniques suggested in the literature (Fox, 2004; Messner, Deane, and Beaulieu, 2002; Pampel and Williams, 2000; Regoeczi and Riedel, 2003). We apply each imputation technique to the SHR, and for cases with information missing in the SHR but known in the police records, we see how well the imputed values correspond both with the individual known values and with the overall distributions in the police records. We discuss the outcome of our assessment of these strategies, and we outline important implications this assessment has for research using SHR data. [source]

Hepatitis B virus and HIV coinfection: relationship of different serological patterns to survival and liver disease

HIV MEDICINE, Issue 5 2007
MK Osborn
Objectives Eighty per cent of HIV-positive patients show evidence of past or current infection with hepatitis B virus (HBV). The impact of chronic HBV infection or the presence of isolated HBV core antibody on survival in the era of highly active antiretroviral therapy (HAART) has not been well studied. Methods This retrospective analysis included patients from the HIV Atlanta Veterans Affairs Cohort Study (HAVACS). This cohort comprises 2818 HIV-positive patients followed since 1982. For this analysis, 1685 patients with available HBV serologies were included, based on laboratory records available since 1992. Adjusted survival analyses were performed for patients showing any of four serological patterns for HBV: (1) surface antigen positive (chronic HBV infection), (2) isolated core antibody, (3) surface antibody with or without core antibody (resolved/vaccinated) and (4) no HBV markers (negative group). Risk factors for liver disease were identified. Results A trend was seen for a lower survival rate from AIDS to death in the chronic HBV infection group compared with the negative group [hazard ratio (HR) 1.43; P=0.118]. The only independent predictor of lower survival rate was hepatitis C virus positivity (HR 1.62; P=0.008). Protective factors were use of HAART (HR 0.40; P=0.0003), use of lamivudine (HR 0.36; P<0.0001) and use of tenofovir (HR 0.23; P<0.0001). Survival from HIV diagnosis to death was not different among the HBV groups. Isolated core antibody patients did not have a lower survival rate compared with those with resolved HBV infection. Patients with chronic HBV infection were 3.5 times more likely to have liver disease than those with no HBV infection (P<0.02). Conclusions There is a trend towards a lower survival rate in patients with HIV and chronic HBV infection, but the difference did not reach statistical significance. The presence of isolated core antibody was not associated with a lower survival rate. [source]

The Walker Project: a longitudinal study of 48 000 children born 1952,1966 (aged 36,50 years in 2002) and their families

PAEDIATRIC & PERINATAL EPIDEMIOLOGY, Issue 4 2004
Gillian Libby
Summary The Walker cohort is a database of over 48 000 birth records that has recently become available. It contains meticulously recorded details of pregnancy, labour, birth and care before discharge for babies born in hospital in Dundee, Scotland between 1952 and 1966. These babies accounted for 75% of all births in Dundee at this time. Over 34 000 (73%) of these subjects can be identified and this presents the opportunity to link this birth information with a large number of current health-outcome databases covering both primary and secondary care. Further, it allows linkage of records across siblings and over two and, in future, three generations. The number of birth records available and linkage to current databases make this a unique birth cohort with huge potential for the investigation of the fetal origins of adult disease. [source]

Floristic changes in the British Isles: comparison of techniques for assessing changes in frequency of plants with time

BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2006
TIM C. G. RICH
Botanical recording data are often used to assess changes in the frequencies of plant species over time, but are subject to marked variations in recording activity. We compare and evaluate some general methods that can be used to detect changes in species' frequencies taking into account the recording variations. Models for 15 species that have been studied in detail previously were compared using the numbers of individual records, sites, hectads, or vice-counties at different time scales (year, decade, moving averages, and pre-/post- specific dates), with or without correction for recording variation. The best methods had a correction for the amount of recording over time, summarized records by decade or moving average, and used an extrapolation between first and last records for sites or hectads. Increasing the geographical and temporal scales can decrease the influence of recording variations, but leads to a loss of sensitivity and under-estimates the true extent of change. The choice between sites and hectads will depend on the detail of the records available; cruder data sets should use the latter. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 152, 279,301. [source]