Overview of Study Designs.pdf
- 1. Overview of Study Designs Shamim Namukasa
- 2. Objective • To distinguish the characteristics of epidemiologic study designs
- 3. Study design: Definition A study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis/questions into an operational one.
- 4. Choice of Design Depends on Depends on: –Research Questions/Goals –Researcher Skills –Time and Funds –Nature and availability of information –Occurrence of disease
- 5. Study Designs: Types • Qualitative • Quantitative –Experimental –Observational
- 9. Major Epidemiologic Study Designs • Descriptive - patterns and frequency of disease (Who, What, When, and Where) • Descriptive – Case report – Case series • Analytic- determinants and risk of disease (Why and How) – Randomized – Non-randomized • Quasi experiment • Cohort – Retrospective – Prospective • Case-control • Cross-sectional • Longitudinal • Ecologic Adapted from Koepsell and Weiss. Epidemiologic Methods: Studying the Occurrence of Illness. Oxford University Press 2003; P. 94
- 10. Descriptive studies • Undertaken without a specific hypothesis • Among the earliest studies on a new disease – Characterize disease entity – Quantify frequency and how it varies in relation to person, place, time
- 11. Descriptive studies • Case reports – “…careful, detailed report by one or more clinicians of the profile of a single patient.” (Hennekens & Buring. Epidemiology in Medicine. Little Brown and Company, 1987; P. 18)
- 13. Descriptive Studies • Case series – Characteristics of a group of individuals with a given clinical outcome
- 14. Case series: Requirements for interpretation To make sense of case-series data the key requirements are: • The diagnosis (case definition) or, for mortality, the cause of death • The date when the disease or death occurred (time) • The place where the person lived, worked etc (place) • The characteristics of the person (person) • The opportunity to collect additional data from medical records (possibly by electronic data linkage) or the person directly
- 16. Consider • A study with the goal of determining whether physical activity reduces the risk of heart disease.
- 17. Analytic Studies • Undertaken to test a hypothesis • Relate/association of a health outcome to a potential determinant/exposure – Genetic – Environmental – Behavioural • Does the determinant cause the outcome?
- 19. Abstract Objective To test the efficacy of installing safety devices in the homes of young children on total injury rates and on injuries deemed a priori modifiable by the installation of these devices. Design A nested, prospective, randomized controlled trial. Setting Indoor environment of housing units. Participants Mothers and their children from birth to 3 years old participating in the Home Observation and Measures of the Environment study. Among 8878 prenatal patients, 1263 (14.2%) were eligible, 413 (32.7%) agreed to participate, and 355 were randomly assigned to the intervention (n = 181) or control (n = 174) groups. Intervention Installation of multiple passive measures (eg, stair gates, cabinet locks, and smoke detectors) to reduce exposure to injury hazards. Injury hazards were assessed at home visits by teams of trained research assistants using a validated survey. Main Outcome Measure Modifiable and medically attended injury (ie, telephone calls, office visits, and emergency visits for injury). A Randomized Controlled Trial of Home Injury Hazard Reduction: The HOME Injury Study Kieran J. Phelan, MD, MS; Jane Khoury, PhD; Yingying Xu, MS; et al Arch Pediatr Adolesc Med. 2011;165(4):339-345. doi:10.1001/archpediatrics.2011.29
- 20. time Study begins here (baseline point) Study population Intervention Control outcome no outcome outcome no outcome baseline future RANDOMIZATION
- 21. Randomized Controlled Trials Source Population Eligible Ineligible Consent to Participate Decline to Participate Random Assignment Experimental/Interevention Control Outcome No Outcome Outcome No Outcome From Koepsell and Weiss. Epidemiologic Methods: Studying the Occurrence of Illness. Oxford University Press 2003; P. 94
- 22. Abstract Objective To test the efficacy of installing safety devices in the homes of young children on total injury rates and on injuries deemed a priori modifiable by the installation of these devices. Design A nested, prospective, randomized controlled trial. Setting Indoor environment of housing units. Participants Mothers and their children from birth to 3 years old participating in the Home Observation and Measures of the Environment study. Among 8878 prenatal patients, 1263 (14.2%) were eligible, 413 (32.7%) agreed to participate, and 355 were randomly assigned to the intervention (n = 181) or control (n = 174) groups. Intervention Installation of multiple passive measures (eg, stair gates, cabinet locks, and smoke detectors) to reduce exposure to injury hazards. Injury hazards were assessed at home visits by teams of trained research assistants using a validated survey. Main Outcome Measure Modifiable and medically attended injury (ie, telephone calls, office visits, and emergency visits for injury). A Randomized Controlled Trial of Home Injury Hazard Reduction: The HOME Injury Study Kieran J. Phelan, MD, MS; Jane Khoury, PhD; Yingying Xu, MS; et al Arch Pediatr Adolesc Med. 2011;165(4):339-345. doi:10.1001/archpediatrics.2011.29
- 23. Quasi-Experiment Source Population Eligible Ineligible Consent to Participate Decline to Participate Non-Random Assignment Experimental/intervention Control No Outcome Outcome No Outcome Outcome Adapted from Koepsell and Weiss. Epidemiologic Methods: Studying the Occurrence of Illness. Oxford University Press 2003; P. 94
- 25. • Study groups defined in terms of exposure and followed to determine frequency of outcome • Prospective cohort Study • Retrospective or historical Cohort study • Studies can have both prospective and retrospective components • Several outcomes could be studied at the same time; suitable for incidence estimation. Even though it is expensive; time-consuming; inefficient for rare diseases Cohort Study Exposure ? Study Begins ? Disease Exposure ? ? Disease Study Begins
- 26. • A cohort study was designed to assess the impact of sun exposure on skin damage in beach volleyball players. During a weekend tournament, players from one team wore waterproof, SPF 35 sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball tournament players' skin from both teams was analyzed for texture, sun damage, and burns. Comparisons of skin damage were then made based on the use of sunscreen. The analysis showed a significant difference between the cohorts in terms of the skin damage.
- 29. Which clinical questions does this study design best answer?
- 30. time Study begins here Study population free of disease Factor present Factor absent disease no disease disease no disease present future
- 32. Case-control Studies • Subjects are selected on outcome status (disease / no disease) • Look back to determine exposure status least expensive; least time-consuming; suitable for study of rare diseases (especially NCDs) Exposure ? Study Begins ? Disease From Hennekens & Buring. Epidemiology in Medicine. Little Brown and Company, 1987; P. 24 Time
- 34. Cross-sectional Study • Outcome and exposure status determined at same point in time • Survey/snap shot in time • Detects point prevalence Exposure Outcome Time From Koepsell and Weiss. Epidemiologic Methods: Studying the Occurrence of Illness. Oxford University Press 2003; P. 94
- 36. • Longitudinal studies often use surveys to collect data that is either qualitative or quantitative.
- 37. • An analytical study tries to answer how or why a certain outcome might occur. • A descriptive study only summarizes said outcome using descriptive statistics. • A descriptive study might look at the prevalence of obesity in children, while an analytical study might examine exercise and food habits in addition to obesity levels to explain why some children are much more likely to be obese than others.
- 38. Advantages • Because you only collect data at a single point in time, cross-sectional studies are relatively cheap and less time-consuming than other types of research. • Cross-sectional studies allow you to collect data from a large pool of subjects and compare differences between groups. • Cross-sectional studies capture a specific moment in time. National censuses, for instance, provide a snapshot of conditions in that country at that time.
- 39. Disadvantages • It is difficult to establish cause-and-effect relationships using cross-sectional studies, since they only represent a one-time measurement of both the alleged cause and effect. • Since cross-sectional studies only study a single moment in time, they cannot be used to analyze behavior over a period of time or establish long-term trends. • The timing of the cross-sectional snapshot may be unrepresentative of behavior of the group as a whole. For instance, imagine you are looking at the impact of psychotherapy on an illness like depression. If the depressed individuals in your sample began therapy shortly before the data collection, then it might appear
- 40. Advantages of longitudinal studies • Greater validation: For a long-term study to be successful, objectives and rules must be established from the beginning. As it is a long-term study, its authenticity is verified in advance, which makes the results have a high level of validity. • Unique data: Most research studies collect short-term data to determine the cause and effect of what is being investigated. Longitudinal surveys follow the same principles but the data collection period is different. Long-term relationships cannot be discovered in a short-term investigation, but short-term relationships can be monitored in a long-term investigation. • Allow identifying trends: Whether in medicine, psychology, or sociology, the long-term design of a longitudinal study enables trends and relationships to be found within the data collected in real time. The previous data can be applied to know future results and have great discoveries. • Longitudinal surveys are flexible: Although a longitudinal study can be created to study a specific data point, the data collected can show unforeseen patterns or relationships that can be significant. Because this is a long-term study, the researchers have a flexibility that is not
- 41. Disadvantages of longitudinal studies Research time • The main disadvantage of longitudinal surveys is that long-term research is more likely to give unpredictable results. For example, if the same person is not found to update the study, the research cannot be carried out. It may also take several years before the data begins to produce observable patterns or relationships that can be monitored. • An unpredictability factor is always present • It must be taken into account that the initial sample can be lost over time. Because longitudinal studies involve the same subjects over a long period of time, what happens to them outside of data collection times can influence the data that is collected in the future.
- 42. • Some people may decide to stop participating in the research. Others may not be in the correct demographics for research. If these factors are not included in the initial research design, they could affect the findings that are generated. • Large samples are needed for the investigation to be meaningful • To develop relationships or patterns, a large amount of data must be collected and extracted to generate results. Higher costs • Without a doubt, the longitudinal survey is more complex and expensive. Being a long-term form of research, the costs of the study will span years or decades, compared to other forms of research that can be completed in a smaller fraction of the time. • The advantages and disadvantages of longitudinal studies show us that there is enormous value in the ability to find long-term patterns and relationships, so it is important to plan and take the necessary
- 43. Longitudinal studies Cross-sectional studies Longitudinal studies take a longer time, from years to even a few decades. Cross-sectional studies are quick to conduct compared to longitudinal studies. A longitudinal study requires an investigator to observe the participants at different time intervals. A cross-sectional study is conducted over a specified period of time. Longitudinal studies can offer researchers a cause and effect relationship. Cross-sectional studies cannot offer researchers a cause-and-effect relationship. In longitudinal studies, only one variable can be observed or studied. With cross-sectional studies, different variables can be observed at a single moment. Longitudinal studies tend to be more expensive. Cross-sectional studies are more accessible for companies and researchers.
- 46. Observational studies-Group level Ecological studies • Data from entire populations compared for outcome frequency • Ecological studies – The unit of observation is geographic population or community. – Disease rates and exposures are measured in each of a series of populations and their relation is examined. – Disease and exposure is abstracted from published statistics and therefore does not require expensive or time consuming data collection. • Examples: – Change in average community viral load after the introduction of ART
- 49. In-class Assignment Assign one of the study designs outlined in class to each study description
- 50. 1. Investigators select all patients presenting to an Emergency Department with a skiing injury and describe their characteristics and the type and nature of the injuries. 2. A number of soccer teams were assigned at random to receive a pre-season training program to increase balance and proprioception. The remaining teams received a standard pre-season fitness program. The rate of injuries in the wobble board group was compared with the standard fitness training group.
- 51. Overlap in the conceptual basis of quantitative study designs • The cross-sectional study can be repeated • If the same sample is studied for a second time i.e. it is followed up, the original cross-sectional study now becomes a cohort study. • If, during a cohort study, possibly in a subgroup, the investigator imposes an intervention, a trial begins. • Cohort study also gives birth to case-control studies, using incident cases (nested case control study). • Cases in a case-series, particularly a population based one, may be the starting point of a case-control study or a trial. • Not every epidemiological study fits neatly into one of the basic designs.
- 52. Qualitative study designs • https://slideplayer.com/slide/4350633/