1. unit 3 part I- intro with (a) Observational studies – descriptive and analytical designs & (b )Ecological.pdf
- 1. Unit 3: Epidemiological study designs and research ethics Part I Ashesh Malla 1
- 2. Acknowledgement • This presentation has been prepared with the help of many books and presentations on the topic. • The presenter pays his sincere gratitude to all authors, professors and experts for their efforts and contributions. • There will be no claim for IPR. However, if you use these slides as it is, do not forget to acknowledge. 2
- 3. Objective of this session • To understand about epidemiological study design, • To study about type of study designs ✓ Observational studies – descriptive and analytical designs ✓ Ecological studies 3
- 4. Concept-Epidemiological study design • In epidemiology, researchers are interested in measuring or assessing the relationship of exposure with a disease or an outcome. • As a first step, they define (the hypothesis based on) the research question and then decide which study design will be best suited to answer that question. • How the researcher conducts the investigation is directed by the chosen study design. 4
- 5. Epidemiological study design … • A epidemiological study design is the conceptual structure with which a research is conducted. • It is blueprint for answering the research question. • It is the plan for collection, measurement and analysis of data. • It deals with who, what, where, when, how much and why. • Eg, House map 5
- 6. Study designs… • Choosing the appropriate study design is an important step in any epidemiological research • Each study design has strengths and weaknesses. • Researchers must consider all sources of bias and confounding, and strive to reduce them • Ethical issues are important and ethical implications differ according to the study design 6
- 7. Study design based on time period of study On the basis of time period of the study, epidemiological studies are of two types: − Cross-sectional study: The study is done at one point in time. − Longitudinal study: Longitudinal study is done over a prolonged period of time by means of follow up examinations. 7
- 8. Type of study design Observational study Interventional study Explorative study Descriptive study Analytical study Quasi-experimental study Experimental study Randomized controlled trials Field trials Community trials
- 9. Observational study • Observational studies allow nature to take its course: • the investigator measures but does not intervene. • So, the study to observe natural processes where there is no any intervention or manipulation. • An observational study can be either be explorative, descriptive or analytical.
- 10. Exploratory study • Preparatory design of epidemiological study, • Design carried out in order to determine the nature of problem when little is known about it, • Explore the research questions but doesn’t not offer solution to existing problem, • Just helps to have a better understanding of the poorly researched problem, • Gives room for further research 10
- 11. Exploratory study… • So, it is the initial study to decide − research design − sampling method − & data collection method • Mostly qualitative in nature, • Could be flexible and informal, • Concept generation 11
- 12. Advantages of Exploratory study • Flexibility of data source and are dynamic, − Informal discussion with colleagues, patients, seniors, community people, key leaders, etc − Formal structured interviews − Secondary resources such as case study report, pilot studies or other published literatures, • Increased understanding, Knowledge on phenomenon • Generates concept & helps to design research methodology for further studies 12
- 13. Disadvantages of Exploratory study • Generate qualitative information & interpretation of such type of information is judgmental, Subject bias • Problem of representation/generalizability 13
- 14. Descriptive studies • Often the first step in an investigation; • Simple description of the health related states/events w.r.t. time, place & person; Answer what, who, where, and when; • Provides the foundation for the formulation of hypothesis; • Pure descriptive studies make no attempt to analyze the links between exposure and effect; • Both qualitative and quantitative methods are used for data collection; • Data analysis – measure of central tendency/measure of dispersion, frequency, rates, proportion & ratio.
- 15. Maternal mortality rates in Sweden, 1750-1975
- 16. Descriptive studies • Such data can be of great value when identifying factors that have caused such a clear downward trend. • During 1860s and 1870s there was great poverty in Sweden thus adversely affecting the living conditions of women which might have caused the temporary rise in maternal mortality at that time. • During that period, almost one million Swedes emigrated, most of them to the US
- 17. Procedures in descriptive studies 1. Defining the population 2. Defining the disease under study 3. Describing the disease in terms of time, place and person 4. Measurement of disease 5. Comparing with known indices 6. Formulation of an aetiological hypothesis 17
- 18. Descriptive studies – procedures • Defining population • Clearly mentioned criteria – whole or sample or high risk • Large enough to compute the measurements meaningfully • Crucial in epidemiological study Population at risk • Population used as denominator for calculating rate, ratio and proportions • Defining disease under study • Precise and valid definition- operational defn • Case definition must be adopted throughout
- 19. Procedures -Describing the disease • Time distribution - Time- year, season, month, week, day, duration − Short terms fluctuations: epidemic (road accidents), outbreak (food poisoning) − Periodic fluctuations: seasonal (JE in rainy) /cyclic trend (Measles) − Long term or secular trends: several years (TB, Malaria) • Place distribution - International variation eg stomach ca, - National eg malaria, - Rural-urban eg mental illness, - Local distributions eg Kalaazar • Person distribution − Person- age, sex, ethnicity, occupation, class, stress, migration, marital status
- 20. Descriptive studies Procedures... • Measurement of disease oAfter defining, the disease load should be measured in population, oMeasured in terms of mortality, morbidity - prevalence, incidence. oCross-sectional/prevalence study – one point in time – chronic diseases oLongitudinal/incidence study- over a prolonged time – natural history • Comparing with known incidences oWith different population/groups oFrom previous studies – local, regional, national, international indicators • Formulation of a hypothesis oRelating to disease aetiology oAccepted or rejected using analytical studies
- 21. Types of descriptive studies • Case study/ case series • Community diagnosis/ need assessment • Survey ✓ Descriptive cross-sectional design ✓ Descriptive ecological study design 21
- 22. Case study • Based on reports of a series of cases of specific condition or a series of treated cases; • If single case case-study • If series case series • Story of success or may be failure H0 formulation • Most imp no control group • Case series represent the numerator of disease occurrence, • Denominator Total cases • Describes unusual care practices, complex diagnosis and nobel treatments in epidemiological studies. 22
- 23. Case study • Can you estimate risk from case study? • No population at risk • What measurement do you use then? • Only proportion to make case study impressive, • & is presented w.r.t. variables under study eg sex, ethnicity, occupation, age-group, etc 23
- 24. Community diagnosis/need assessment • Comprehensive assessment of the health status of an entire community in relation to its social, physical & biological environment, • Purpose – to define existing problems, determine available resources and set priorities for planning, implementing and evaluating health programmes for community and by the community, • Simple statistics - measure of central tendency/measure of dispersion, frequency, rates, proportion & ratio, 24
- 25. Survey • Simplest form of observational study, • Snapshot of the population at one time, • Measures both exposure and disease during same period, • Unit of analysis - population • A survey is a research method used for collecting data from a predefined group of respondents to gain information and insights into various topics of interest, • Eg, KAP survey of FP 25
- 26. Survey • Simplest form of observational study, • Snapshot of the population at one time, • Measures both exposure and disease during same period, • Unit of analysis – individual; No comparison group; • A survey is a research method used for collecting data from a predefined group of respondents to gain information and insights into various topics of interest, • Eg, KAP survey of FP 26
- 27. Uses of descriptive studies • Provides basic data on Morbidity, mortality & magnitude of the problem • Provides clues to aetiology/hypothesis • Provides background data for • Planning • Organisation • Evaluation • Contributes in research • Providing data on time, place and person
- 28. Advantage of descriptive studies • Can acquire a lot of information through description. It allows you to analyze facts and helps you in developing an in-depth understanding of the research problem; • Some behaviors/situations/health related states or events cannot be studied any other way than descriptive study. It can be used as an indirect test of a theory or model; • It provides data regarding the magnitude of the disease load and types of disease problem in the community in terms of morbidity and mortality; • It provides clues to disease aetiology, and formulation of hypothesis; • Provides background data (prevalence, morbidity & mortality) for Planning, Organisation & Evaluation of health services, helps in trend analysis; • Mix method of data collection; • It is cost-effective and quick; 28
- 29. Disadvantage of descriptive design • Due to the observational nature, it is quite difficult to repeat the research process. • The biggest disadvantage of descriptive research is that you cannot use statistical tools or techniques for verifying problems. • Respondents can be affected by the presence of an observer and may engage in pretending. This is called the “observer effect.” • There are high chances of biases in the research findings. 29
- 30. Analytical design • Observational studies aimed at establishing a relationship between a risk factor and an outcome; • Subject of interest is individual within population; • However, inference is made to the population from which the individual is selected; • Include a comparison group • Answer why and how ? • Hypothesis testing is the primary tool of inference; 30
- 31. Developing Hypotheses • A hypothesis is an educated guess about an association that is testable in a scientific investigation. • Descriptive data (Who? What? Where? When?) provide information to develop hypotheses. • Hypotheses tend to be broad initially and are then refined to have a narrower focus. 31
- 32. Example – Developing Hypothesis • Null Hypothesis: People who smoke shisha are not likely to get lung cancer than people who do not smoke shisha. • Alternative Hypothesis: People who smoke shisha are more likely to get lung cancer than people who do not smoke shisha. • Exposure: smoking shisha • Outcome: lung cancer 32
- 33. Advantage and disadvantage of Analytical studies 33
- 34. Types of analytical designs • Cross-sectional study • Case-control study • Cohort study • Ecological study 34
- 35. Ecological/correlational studies • It is an observational study defined by the level at which data are analysed, namely at the population or group level, rather than individual level. i.e the units of analysis are groups of people rather than individuals, • If we determine whether there is an association between an exposure or characteristics, and risk of disease; and if our unit of analysis is group like family, school or ecological unit (village, town or country), then the study is called ecological study. 35
- 36. Ecological studies… • Ecological studies can be done by comparing populations in different places at the same time or, in a time series, by comparing the same population in one place at different times. • Ecological studies are often used to measure prevalence and incidence of disease, particularly when disease is rare. • The main aim ✓To test the etiological hypothesis, ✓To evaluate the effectiveness of population interventions, 36
- 37. Ecological studies - designs • Generally, three different designs can be used to conduct ecological studies depending on the situation. • Such studies may compare populations or groups using ✓ a multiple-group design – geographical ecological study ✓ periods of time using a time-trend design – longitudinal ecological study ✓ or groups and time using a mixed design – Migrational ecological study 37
- 38. Type of Ecological studies • Geographical: This type of study compares one geography with another by assessing the health of the population of each. Exposures for geographies may also be measured and included in analysis as well as other potential confounding variables such as demographic and socioeconomic information. • Longitudinal: A population is monitored to assess changes in disease over time. Again, confounding factors are often included in analysis. • Migrational: Data of migrant populations are collected and analysed. The unit of interest is neither time nor place, but population type. 38
- 39. Some Ecological studies • Cholera study - The study by John Snow regarding a cholera outbreak in London is considered the first ecological study to solve a health issue. • Diet and cancer - Dietary risk factors for cancer have also been studied using both geographical and temporal ecological studies. • Diet and Alzheimer’s – The first paper linking diet to risk of Alzheimer’s disease was a multi-country ecological study published in 1997. • UV radiation and influenza - the seasonality of influenza and seasonal variations in solar UVB doses is another example of the use of temporal ecological studies. 39
- 40. Why carry out an ecological study? - pros • To monitor population health so that public health strategies may be formulated; • to make largescale comparisons, eg, comparisons between countries, continentals; • To study the relationship between population-level exposure/risk factors and disease, or in order to look at the effect of risk factors on the population; • Some exposures of interest can only be studied with aggregate population level data, i.e. when measurements at individual level are not available, eg. confidentiality might require that individuals are anonymized by aggregation of data to small area level; or • the disease under investigation is rare, requiring aggregation of data for any analysis to be carried out; • The aggregate data used is generally available, so they are quick and inexpensive; • Although other study designs are generally considered more reliable, the population context of individual characteristics has been shown to be a stronger determinant of disease at population level than individual level risk factors. 40
- 41. Cons of ecological study • For an exposure to cause an effect in an individual, the exposure and effect must occur in the same person, but ecologic studies do not have data on individual people, so one does not know if the diseased people were exposed. • There is “ecological fallacy” indicating that risk-associations apparent between different groups of people may not accurately reflect the true association between individuals within those groups. 41
- 42. Ecological fallacy • The ecological fallacy is a type of confounding/bias specific to ecological studies. • It occurs when relationships which exist for groups are assumed to also be true for individuals. • The bias occurs because the association observed between variables at the group level does not necessarily represent the association that exists at the individual level; • An ecological fallacy or bias results if inappropriate conclusions are drawn on the basis of ecological data; • The term “ecological fallacy” means that risk-associations apparent between different groups of people may not accurately reflect the true association between individuals within those groups. 42
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- 44. Ecological fallacy… • An example of an ecological fallacy would be the lack of relationship between maternal deaths and absence of skilled birth attendants in the four regions to the right in Figure. • Clearly many factors other than the presence of a skilled birth attendant impact on the outcome of a delivery. • An ecological fallacy or bias results if inappropriate conclusions are drawn on the basis of such ecological data; • Such ecological inferences, however limited, can provide a fruitful start for more detailed epidemiological work. 44
- 45. Overcome to Ecological fallacy • Multilevel modelling techniques have been developed, where analysis includes both individual and population level data, thus overcoming the ecological fallacy and enabling examination of contextual effects. • Where individual level data are not known or where data are only available in an aggregated form, care must be taken in making causal inferences such as Hill’s criteria for causality in a biological system; to overcome aggregation bias and the ecological fallacy. 45
- 46. Recommended readings • Park – Preventive medicine • “Fundamentals of Epidemiology” by Dr. Anand Ballabh Joshi and Mr. Megha Raj Banjara • Modern epidemiology by Kenneth J. Rothman, Sander Greenland, and Timothy L. Lash • Basic epidemiology by WHO (written by R. Bonita, R. Beaglehole, and T. Kjellström) • Various study design ( https://www.healthknowledge.org.uk/elearning/ epidemiology/practitioners/introduction) • Classification of epidemiological study designs by Neil Pearce (https://academic.oup.com/ije/article/41/2/393/697874)
- 47. •Any comments ? •Any feedbacks ?
- 48. Thank - you