June Juritz

Seasonal variation of suicide in South Africa

Seasonal trends in South African suicide incidence were investigated with a view to ascertaining whether they are consistent with those in the northern hemisphere regarding: (1) the existence of the expected pattern; (2) this pattern being more pronounced for less urbanized groups; and (3) the presence of a secondary fall peak for youth and females. Log-linear modelling was performed to investigate the effect of month and relevant demographic variables on the suicide counts. The 16,389 nationally registered suicide deaths during 1980-1989 were analysed. The expected pattern, with a peak in the spring (that is, in September/October) or summer and a trough in winter, was present. This pattern was more pronounced for a sub-group that is less urbanized and for another sub-group with a relatively low standard of living. The secondary peak in autumn was not present for youth or females. In the northern hemisphere, this secondary peak has been ascribed to sociodemographic factors associated with the commencement of the academic year and (for females) bioclimatic factors associated with gender-specific biological circannual rhythms. The fact that the academic year commences in summer in South Africa indicates that the present findings are consistent with the former explanation.

Parameter Estimation for the Sichel Distribution and its Multivariate Extension

Abstract The Sichel distribution is a three-parameter compound Poisson distribution. It is a versatile model for highly skewed frequency distributions of observed counts and has proved useful in fields as diverse as mining engineering, linguistics, ecology, industrial psychology, and market research. We propose a reparameterization of the Sichel distribution and give an algorithm, which can be implemented on a typical desktop microcomputer, for computing the maximum likelihood estimates of the new parameters. The reparameterization has a number of advantages over the old. In the important two-parameter special case of the Sichel distribution known as the inverse Gaussian Poisson the new parameters are the population mean and a shape parameter, and their maximum likelihood estimators are asymptotically uncorrelated. The reparameterization also lends itself to the convenient multivariate extension presented here. This distribution is well suited for modeling correlated count data whose marginal distribution...

On the Accuracy of Simulated Percentage Points

Abstract Two methods are discussed of obtaining percentage points of distributions by Monte Carlo studies, one using one long run, the other using the average of several smaller runs. The single run has certain advantages that we describe. The two methods are illustrated on percentage points of the normal distribution.

Linear models with an inverse gaussian poisson error distribution

The inverse Gaussian-Poisson (two-parameter Sichel) distribution is useful in fitting overdispersed count data. We consider linear models on the mean of a response variable, where the response is in the form of counts exhibiting extra-Poisson variation, and assume an IGP error distribution. We show how maximum likelihood estimation may be carried out using iterative Newton-Raphson IRLS fitting, where GLIM is used for the IRLS part of the maximization. Approximate likelihood ratio tests are given.

Lymphoma – Emerging realities in sub-Saharan Africa

Substantial geographical differences exist for Hodgkin and other lymphoproliferative disorders with these having previously been documented in a report from the lymphoma reclassification project. In the light of rampant human immunodeficiency syndrome, largely centred in sub-Sahara, this experience is updated in a further 512 consecutive individuals treated over an 8-year period in a privately based academic centre. Median age was 55.2 years 61% were males, 10% had Hodgkin lymphoma and, overall, constitutional symptoms were present in 20%. Prior to referral 19% had received chemotherapy and a further 20% some form of irradiation. Median survival in hairy cell leukaemia (n=14), chronic lymphocytic leukaemia-small lymphocytic lymphoma (n=103), Hodgkin (n=41) and follicular lymphoma (n=59) was not reached at the time of analysis and exceeded 36 months. This was followed by 32 months for those with mantle cell (n=7), splenic (n=2) and extranodal marginal cell (n=11), 24 months for T-cell lymphomas (n=24), 20 months for diffuse large B-cell variants (n=88) but only 12 months for the aggressive tumours exemplified by Burkitt (n=7) and lymphoblastic subtypes (n=6). The remaining 36 patients had to be excluded because numbers were too small for statistical analysis or unreliable staging. Adverse factors were constitutional symptoms, prior treatment with chemotherapy, intermediate or high-risk scores as defined by the international prognostic index, histologic grading and certain anatomical sites of primary tumour. In contrast gender, staging by Rye or Rai classification, retroviral infection and prior treatment with radiotherapy were without effect. Overall survival at 3 years in each category was compared to the curve for the entire cohort and was 100% in hairy cell leukaemia receiving two chlorodeoxyadenosine and greater than 88% in Hodgkin lymphoma treated according to the German study group protocols (p=0.0004). Corresponding figures for chronic lymphocytic leukaemia-small lymphocytic lymphoma were 82% (p=0.0006), follicular lymphoma 71% (p=0.060), peripheral T-cell lymphoma 43% (p=0.0156), diffuse large B-cell lymphoma 39% (p<0.0001), aggressive tumours 25% (p=0.0002) and for the indolent categories including mantle cell, splenic and extra nodal marginal cell lymphomas 22% (p=0.2023). Outcome argues in favour of patient management by a multidisciplinary team implicit in which are standardised protocols for diagnosis, staging and treatment. Under these circumstances the well recognized centre effect applies when results approximate those from first world reference centres. Conversely any deviation from such a disciplined approach is unlikely to achieve comparable benefit and therefore to be strongly discouraged.

Bivariate compound poisson distributions

This paper discusses four alternative methods of forming bivariate distributions with compound Poisson marginals. Basic properties of each bivariate version are given. A new bivariate negative binomial distribution, and four bivariate versions of the Sichel distribution, are defined and their properties given.

Restoration of the Clanwilliam cedar Widdringtonia cedarbergensis: The importance of monitoring seedlings planted in the Cederberg, South Africa

Abstract A decline in numbers of the Clanwilliam cedar Widdringtonia cedarbergensis , an endemic conifer in the fynbos vegetation of the Cederberg mountains, has led to the instigation of a restoration programme to reinstate the species. On the one hand, the loss of fire-sensitive adult trees is reduced by practising frequent, low-intensity burning which precludes the occurrence of intense wild fires. On the other hand, large numbers of nursery-reared seedlings are planted out each year in newly burnt areas of typical cedar habitat. This project investigated the effects of microhabitat factors (shade, aspect, competition from surrounding plants, soil depth) on the survival of transplanted seedlings. Seedling survival was high (39·1–61·2%). It was found that increased shade levels led to the greater probability of seedling survival of recent plantings (18 months prior to the study), but not in plantings performed 5 years earlier. None of the other factors measured affected survival. Seedling transplantings were found to be more efficient than earlier reported seed sowing, since the former resulted in greater survival of seedlings. It is recommended that monitoring is carried out to assess overall success of the programme and suggest future improvement.

Pediatric immunohematopoietic stem cell transplantation at a tertiary care center in Cape Town.

UNLABELLED INTRODUCTION AND STUDY DESIGN: We conducted a retrospective analysis of consecutive referrals of patients under 18 years of age undergoing immunohematopoietic stem cell transplantation to assess the influence of age, diagnosis, graft type and gender on survival. We also contrasted program activity and outcome to that reported from a state hospital in the same geographical area over a comparable period. METHODS Conditioning employed either a sequential combination of fractionated 12Gy whole body and 6Gy total nodal irradiation separated by 120mg/kg of cyclophosphamide in patients over 15 years of age. Alternatively, the latter agent was combined initially with oral busulphan and later the intravenous equivalent. Neuroblastoma cases were prepared using a different regimen. In allografts the harvested product underwent ex vivo T-cell depletion with the humanized version of anti-CD 52 monoclonal antibody designated Campath 1H. No additional immunosuppression was given except where matched unrelated volunteer donors were employed. RESULTS Sixty-eight procedures were carried out in 61 patients over a 6-year period. Of 11 with acute myeloid leukemia, 8 are alive and well whereas 8 of the 14 with the lymphoblastic variant have died. Of the remaining 12 with hematologic malignancy, all but 2 are alive. Ten of the 17 with aplasia are alive as are all with thalassemia or sickle cell disease. None of the four variables tested affected survival. CONCLUSION Our analysis indicates that the standardized preparative regimen, coupled with a now well-established immunosuppressive regimen, is as effective in patients under 18 years of age as in adults. Our analysis also indicates that in a resource-scarce or developing country, it is mandatory to limit high-risk and relatively expensive procedures to active teams that enjoy international accreditation, whether these be in the state or private sector.

Immunohematopoietic stem cell transplantation in Cape Town: A ten-year outcome analysis in adults

BACKGROUND AND OBJECTIVES Immunohematopoietic stem cell transplantation has curative potential in selected hematologic disorders. Stem cell transplantation was introduced into South Africa in 1970 as a structured experimental and clinical program. In this report, we summarize the demography and outcome by disease category, gender, and type of procedure in patients older than 18 years of age who were seen from April 1995 to December 2002. PATIENTS AND METHODS This retrospective analysis included 247 individuals over 18 years of age for whom complete data were available. These patients received grafts mostly from peripheral blood with the appropriate stem cell population recovered by apheresis. RESULTS Patient ages ranged from 20 to 65 years with a median age of 42 years. There were 101 females and 146 males. There were no withdrawals and 63% survived to the end of the study. At 96 months of follow-up, a stable plateau was reached for each disease category. Median survival was 3.3 years (n=6, 14.6%) for acute lymphoblastic anemia, 3.1 years (n=44, 18%) for acute myeloid leukemia, 2.8 years (n=47, 19%) for chronic granulocytic leukemia, 2.8 years (n=71, 29%) for lymphoma, 1.5 years (n=23, 9%) for myeloma, 1.43 years (n=10, 4%) for aplasia, and 1.4 years (n=38, 15%) for a miscellaneous group comprising less than 10 examples each. Multivariate analysis showed that only diagnosis and age had a significant impact on survival, but these two variables might be interrelated. There was no significant difference in outcome by source of graft. CONCLUSION The results confirm that procedures carried out in a properly constituted and dedicated unit, which meets established criteria and strictly observes treatment protocols, generate results comparable to those in a First World referral center. Low rates of transplant-related mortality, rejection and graft-versus-host disease are confirmed, but the benefits cannot be extrapolated outside of academically oriented and supervised facilities.