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Biomedical subjects

Michael Joffe

Publications and source records attributed to Michael Joffe.

13 recordsLinked to original sources
PubMed2006

Complex causal process diagrams for analyzing the health impacts of policy interventions.

Causal diagrams are rigorous tools for controlling confounding. They also can be used to describe complex causal systems, which is done routinely in communicable disease epidemiology. The use of change diagrams has advantages over static diagrams, because change diagrams are more tractable, relate better to interventions, and have clearer interpretations. Causal diagrams are a useful basis for modeling. They make assumptions explicit, provide a framework for analysis, generate testable predictions, explore the effects of interventions, and identify data gaps. Causal diagrams can be used to integrate different types of information and to facilitate communication both among public health experts and between public health experts and experts in other fields. Causal diagrams allow the use of instrumental variables, which can help control confounding and reverse causation.

Audiovisual Aids↗
PubMed2006

The influence of occupational exposure on male reproductive function.

Recently, many studies have found a decrease in semen quality which has increased the focus on male reproductive health. Occupational hazards are by far the best documented in reproductive epidemiological research. Generally, occupational exposures have been divided into physical exposures (heat and radiation), chemical exposures (solvents and pesticides), psychological exposures (distress), exposure to metals and welding. The recent and/or most important epidemiological studies exploring the effect of occupational exposures on semen quality and fecundity, the ability to conceive, are reviewed. The evidence for an adverse effect on male reproduction of several occupational and environmental exposures and toxicants, such as heat, ionizing radiation, inorganic lead, dibromochloropropane, ethylene dibromide, some ethylene glycol ethers, carbon disulfide and welding operations, is strongly supported in well-designed epidemiological studies. For other agents, the association is only suspected or suggested and needs further evaluation before conclusions can be drawn. It is also important to bear in mind that many workers in the non-Western world still are exposed to substances that are banned in the Western world, sometimes in high concentrations.

Fertilization↗
PubMed2005

Studying time to pregnancy by use of a retrospective design.

Biologic fertility can be measured using time to pregnancy (TTP). Retrospective designs, although lacking detailed timed information about behavior and exposure, are useful since they have a well-defined target population, often have good response rates, and are simpler and less expensive to conduct than prospective studies. This paper reviews retrospective TTP studies from a methodological viewpoint and shows how methodological problems can be avoided or minimized by appropriate study design, conduct, and analysis. Sensitivity analyses using data from four European retrospective TTP studies are presented to explore the issues. Although the identified biases tend to have small impacts, the effects are not systematic across studies, and sensitivity analyses are recommended routinely. Planning bias can be checked by comparing propensity to report contraceptive failures in different exposure groups. Medical intervention bias can be avoided by censoring and inclusion of unsuccessful pregnancy attempts. Truncation bias can be a serious problem if unrecognized, but it is avoidable with appropriate study design and/or analysis. Behavior change bias can be minimized by assessing the covariates at the beginning of unprotected intercourse. More complete inference is possible if the study design covers the whole population, not just those who achieve a pregnancy.

Bias↗
PubMed2003

Invited commentary: the potential for monitoring of fecundity and the remaining challenges.

In the epidemiologic study of reproductive capacity, the assessment of fecundity as a functional measure is complementary to approaches that focus on biomedical mechanisms and/or that use biomarkers such as semen quality. More research is needed on time trends, spatial patterns, and particular groups, especially those exposed to potentially toxic agents. Although specific research projects will always be important, much could be gained by general population surveillance, which could be introduced into existing multipurpose surveys and repeated periodically. The core measurement would be time to pregnancy, which can be carried out using a short, acceptable questionnaire that has good validity at the group level. This should be accompanied by questions on time periods of unprotected intercourse that do not end with conception, to avoid bias resulting from exclusion of relatively infertile couples. Information is also required on contraceptive failures, recent contraceptive use, and other covariates and possibly on behavioral variables, such as the degree of planning and persistence in trying to conceive, and couples' knowledge of fertile days of the menstrual cycle. Existing statistical methods can deal with possible biases due to "accidental" pregnancies and the effects of fertility treatment. Further methodological work is needed to avoid or measure more subtle biases, for example, to determine the best way to deal with pregnancies occurring to couples whose approach to family formation is relaxed, for whom the concept of "pregnancy planning" does not apply.

Female↗
PubMed2003

Infertility and environmental pollutants.

While it has long been known that female fertility is impaired by oestrogen exposure, it is unclear whether environmental pollutants with weak oestrogenic effects are sufficiently potent and prevalent to have biological effects in humans. Male fertility, or sperm concentration at least, appears to have deteriorated, and there is substantial spatial variation at both national and global level, as well as a genetic component. Sperm morphology and motility are implicated too. There is good evidence for an increase in testicular cancer, and possibly in other conditions that certain spatial characteristics plus evidence on heritability suggest are linked to impaired spermatogenesis. A candidate agent would need to have started increasing in the early 20th century. Weak environmental oestrogens are not responsible. Candidates include agents affecting endogenous maternal oestrogen levels, environmental anti-androgens (although these cannot explain the epidemiological findings), and dioxin and related compounds. Genetic damage should be considered as a unifying hypothesis, possibly focused on the Y-chromosome.

DNA Damage↗
PubMed2003

Health impact assessment in relation to other forms of impact assessment.

Health impact assessment (HIA) has many advocates for its use to identify and optimize the health effects of non-healthcare interventions. It is an assessment of the health effects, positive and negative, of a project, programme, or policy. Expertise developed in the United Kingdom from a realization that health impacts are often overlooked during the planning stages of development projects but prior planning can avoid detrimental effects. Considering health impacts is now recommended in all continents; the focus has moved from less to more developed countries and upstream from projects to policies. Health impact assessment shares certain concepts and methods with risk assessment, environmental impact assessment, strategic environmental assessment, social impact assessment, and economic assessments. This paper describes the development of health impact assessment and its relation to these other forms of impact assessment.

Decision Making, Organizational↗