Concept of Causation and common Epidemiological study designs.
Name: Confucius Aligo Allison Amba
Objective of this paper is to explain the concept of ‘Causation’ and explain of some common epidemiological study designs
Causation is defined as the capability of one variable to influence another. The first variable may bring the second into existence or may cause the incidence of the second variable to fluctuate. “Causality is a genetic connection of phenomena through which one thing (the cause) under certain conditions gives rise to, causes something else (the effect)” (Alexander 1983)1
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The concept of causation was first described by Plato he stated that “everything that becomes or changes must do so owing to some cause, for nothing can come to be without a cause” (Menno)2. The stoics stated that “cause is linked both to an exceptionless regularity and to necessity. They strictly hold to the view that each event has a cause” (Menno). A cause of disease is “an event, condition, characteristics or combination of these factors which plays an important role in producing the disease” (JLI Video Lecture note – 3rd Lesson of Epidemiology).
Common Epidemiological study designs
The word epidemiology comes from the Greek word “epi, meaning on or upon, demos, meaning people, and logos, meaning study of”3 the Epidemiology is the “study of the distribution of disease and determinants of health-related states or events in specified human population and the application of this study to the control of human health problem”(CDC)3. Epidemiology is “data-driven and relies on a systematic and unbiased approach to the collection, analysis and interpretation of data. It also draws on methods from other scientific fields including biostatistics and informatics, with biologic, economic, social and behavioral sciences” (CDC).
Epidemiological studies are conducted using human population to determine causal relation between factors that and individual or population is expose to and the health effect of the exposure. The epidemiological studies designs can be classified either as observational or experimental. (JLI Video Lecture note – 3rd Lesson of Epidemiology).
Experimental study designs
Experimental studies can be randomized controlled, non-randomized control, field trail studies and community trials.
- Randomized controlled trail (RCT), alternative name clinical trials (JLI lecture note – 3rd Lesson of Epidemiology) in this study “people are allocated at random to receive one of several clinical interventions”4 one of the group is a control which may be given a placebo or no intervention. This study is “quantitative, comparative, controlled experiments in which investigators study two or more interventions in a series of individuals who receive them in random order. The RCT is one of the simplest and most powerful tools in clinical research” (MedicineNet.com). This study is termed as “gold standard” (http://www.bmj.com/content/348/bmj.g4115) that determines the effectiveness of treatment.
- Non-randomized controlled trails this is a study in which is assigned to an intervention alternate and not random. Participants may be volunteers who accept to participate in the study.
- Field trials are study design where the intervention strategies are assigned to healthy individuals within the community.
- Community trials alternative name community interventions studies (JLI Video Lecture note – 3rd Lesson of Epidemiology) are mostly preventive; interventions are assigned to all community members in the study area. The advantages include easier changing the community social environment; interventions are tested in actual natural conditions and cheaper (Omar 2006)5
Observational study designs
Observational studies can be either descriptive or analytic studies. Observational studies allows nature to take place; “the investigator measures but does not intervene”. (JLI Video Lecture note – 3rd Lesson of Epidemiology).
Descriptive studies are studies that are design to describe occurrence of disease by time, place and person, while analytic studies are studies designed to examine etiology and causal association. “A descriptive study is limited to a description of the occurrence of a disease in a population and is often the first step in an epidemiological investigation”. (JLI Video Lecture note – 3rd Lesson of Epidemiology).
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Descriptive epidemiological study design describes the occurrence of disease or the determinants within a population. Descriptive epidemiological study generates hypothesis and answer the questions WHAT, WHO, WHERE & WHEN? The WHO refers to person and characteristic such as (age, sex, occupation), WHERE refers to place that is location (residence, work or hospital). WHEN refers to time (includes diagnosis, test and reporting), descriptive studies can be “geographical or ecological also known as ecological correlational studies examine population, can be used to demonstrate patterns of disease and associated factors in a population and unit of study are populations or groups”6. The advantage of ecological studies include use of routine collected health statistics, cheap and simple to conduct, generate hypothesis to examine at individual level; and the disadvantages includes lack of available data on confounding factors, difference between areas in measurement of exposure and difference in recording disease frequency (healthknowldge.org.uk, David AG., Kenneth FS., 20027). The other major type of descriptive study is individual study “individuals studies are case reports, case-series report, cross-sectional studies and surveillance” (David AG., Kenneth FS., 2002).
Case-series report this combine individual medicine information in one report or “appearance of several similar cases in a short period heralds an epidemic” (David AG., Kenneth FS., 2002).
Case report this is an observation reported by a clinician. This mean lead to case-control studies to determine the association of the outcome to the exposure for example long term use of specific medication (David AG., Kenneth FS., 2002)
Cross-sectional studies this is also referred to as prevalence study and is used to describe the health of a population, this can be study in small population with particular exposure for example employee in a factory (David AG., Kenneth FS., 2002)
Surveillance study this can be done as active or passive ongoing collection, analysis and interpretation of health data. In order to determine control and preventive measure to any identified health condition (David AG., Kenneth FS., 2002).
Ecological study also called co-relational studies “the unit of analysis is population or groups of people rather than individuals” (JLI Video Lecture note – 3rd Lesson of Epidemiology). This study “look for associations between exposures and outcomes in population” (David AG., Kenneth FS., 2002). This type of study is simple to conduct, interpretation is often difficult and it’s difficult to link individual to exposure and effect. (JLI Video Lecture note – 3rd Lesson of Epidemiology).
Analytical study design
Analytical epidemiological study design aims to gain understanding on the quality and the impact of the diseases determinants on the occurrence of disease. Analytical studies can cohort study, case control study and cross-sectional study
- Cohort Study is the study that identify individuals based on their exposure status, this study consider two group of people expose and non- exposed in order to follow the disease outcome whether disease or non-disease, the “study participant are followed overtime-form weeks to years; and the study group share characteristics for example in birth cohort”8. The advantage of this study include estimation of the risk, can look at multiple outcomes, can investigate the potential natural history of disease and the disadvantages include requires large population, not suitable for rare outcome or exposure, expensive and time consuming.
- Case Control Study are retrospective they normal look back. In this study the cases have the condition and the controls are not, its looks back to identify the risk factors associate with the disease. in this study “the prevalence of exposure to a potential risk factor (s) is compared between cases and controls”6
- Cross-Sectional Study this study is used to determine the “prevalence of the outcome of interest for a given population”9. This studies can assess multiple out come and risk factors, useful for public health planning and disease etiology, takes little time and not expensive, can estimate prevalence of outcome of interest. With this study prevalence-incidence bias may occur and difficult to make causal inference (Kate 2006).
- Occupational epidemiological study this study designed select working people with particular jobs or exposure as the subjects for the study. Workers have high exposure to certain risk factors than the usual population, due to their risk exposure the probability of finding and effect is high if any true effects exist. However, the outcome of this study many not be generalized to the overall population and even worker with may have different risk from each other.
- Alexander Spirkin (1983) Dialectical Materialism © 1983 by Progress Publishers available at https://www.marxists.org/reference/archive/spirkin/works/dialectical-materialism/intro01.html accessed on 2015/06/17
- Menno Hulswit A Short History of Causation University of Nijmegen, The Netherlands available at http://see.library.utoronto.ca/SEED/Vol4-3/Hulswit.htm accessed on 2015/06/17
- Centre for Disease Control and Prevention Principles of Epidemiology in Public Health Practice, Third Edition An Introduction to Applied Epidemiology and Biostatistics CDC 24/7: Saving Lives, Protecting People available at http://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson1/section1.html
- MedicineNet.com Definition of Randomized controlled trail available at http://www.medicinenet.com/script/main/art.asp?articlekey=39532 access on 2015/06/16
- Omar Kasule Islamic Medical Education Resources -04 0611-Randomized Design: Community Trials synopsis of lecture for MPH candidates at university Malaya on Friday November 3, 2006 available at http://omarkasule-04.tripod.com/id1033.html
- Health Knowledge Education, CPD and Revalidation from Phast Introduction to study designs 1a – Epidemiology available at http://www.healthknowledge.org.uk/public-health-textbook/research-methods/1a-epidemiology
- David AG.; and Kenneth FS (2002). Descriptive Studies: what they can and cannot do Epidemiological Series Lancet 2002; 359:145-49 available at http://www.m-publichealth.med.uni-muenchen.de/download/mph/mph_wintersemester_2012_2013/epidemiologie/epigrimesdescriptive.pdf accessed on 2015/06/18.
- Institute for work & Health Research Excellence Advancing Employee health what researchers mean by — cohort study available at http://www.iwh.on.ca/wrmb/cohort-study accessed on 2015/06/16
- Kate Ann Levin Study design III: Cross-sectional studies Evidence-Based Dentistry (2006) Dental Health Service Research Unit, University of Dundee, Scotland, UK. 7, 24-25.Doi:10.1038/sj.ebd.6400375 available at http://www.nature.com/ebd/journal/v7/n1/full/6400375a.html accessed on 2015/06/16
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