1Methods in Injury ResearchStudy Design ModulesThomas Songer, PhDUniversity of PittsburghSeveral different types of injury studies can be found in the literature. The purpose of this lecture is to illustrate the various forms of study designs used in injury research, and to highlight their strengths and weaknesses, using current studies.2Study DesignsCase reportCase seriesDescriptiveEpidemiologyEcologicDescriptiveRCTBefore-AfterstudyCross-sectionalstudyCase-CrossoverstudyCase-ControlstudyCohort studyAnalyticAs Koepsell has illustrated in the book, “Injury Control”, injury studies may be descriptive in nature (describing the frequency or characteristics of injury events) or analytic (testing relationships between common traits and injury). Differing forms of descriptive studies exist. These designs are outlined in the next slide.Analytic studies include experimental designs (the randomized controlled trial) and observational designs (case-control studies, cohort studies, etc.). The case-crossover study design has received a lot of attention in the injury field in the last five years.3Case ReportCase SeriesDescriptiveEpidemiology StudyOne case of unusualinjury findingMultiple cases ofinjury findingPopulation-based cases with denominatorEcologic StudyCorrelation study oftwo factorsDescriptive study designs include case reports, case series, incidence studies, and ecologic studies. The case report is the most elementary study design in the literature. It generally describes an injury or injuries to one or two individuals that have been identified in a medical setting. There is also usually a unique feature to the noted injury (by cause, by nature of injury, etc.). The case series design is an extension of the case report. In a case series, a number of events are described. These events usually have been observed over a set period of time (such as one year) and are identified from one reporting source (e.g. a hospital).The descriptive epidemiology study is noted by the collection of injuries over a defined population base and by the use of denominator data to determine rates. The most frequent information generated from these designs are incidence rates for injuries. The ecologic study is a hypothesis generating study. Usually using group-level data, it examines if two factors are correlated with each other.4Prospective Cohort studyMeasure exposureand confoundervariablesExposedNon-exposedOutcomeOutcomeBaselinetimeStudy begins hereCase-control studies are perhaps the most frequent form of analytic study designs used in the injury field. These designs are very good for events that are rare in occurrence, and one could argue that severe injuries are relatively rare.Still, there are some situations where cohort study designs would be appropriate in the injury field. Most notably for less severe forms of injury. The classic design in a cohort study is shown here. The study begins by assessing baseline levels of the exposure and other variables. Study subjects are then followed on a regular basis to identify the outcome. The frequency of outcomes are tested between persons who had exposure to the possible risk factor at baseline and persons with no exposure.5Retrospective Cohort studyMeasure exposureand confoundervariablesExposedNon-exposedOutcomeOutcomeBaselinetimeStudy begins hereAn alternative form of the cohort study is something termed the retrospective cohort study. Other researchers may also call this a historical prospective study. This design is nearly identical to the prospective cohort study. The sequence of baseline exposure determination and longitudinal follow-up for outcomes is similar. The difference lies in the time in which the study begins. In this retrospective design, the researcher constructs the cohort study by looking back in time and placing data in the appropriate order and sequence. These studies are possible to do with large medical databases, such as the membership files of the Health MaintainanceOrganizations, or the medical files in the Scandinavian countries.6Descriptive StudiesCase-control StudiesCohort StudiesDevelop hypothesisInvestigate it’srelationship tooutcomesDefine it’s meaningwith exposuresThis slide is presented as a matter of review to illustrate the following points.1. Descriptive studies are useful for identifying hypotheses to test in analytic studies. 2. Case-control studies are then usually applied to evaluate if the hypothesized factor is related to the outcome of interest. Case-control studies generally illustrate if a factor is associated with an injury. It does not assign causation to the role of the risk factor. 3. Subsequently, cohort or longitudinal studies are applied to further define the importance of exposure to the causal agent for the development of the outcome. Cohort designs allow for investigators to make causal inferences for injuries.7• Study design• Definition of injury• Data Sources• Severity of Injury• Population•Bias• FindingsElements of each studyThe elements outlined here will be examined in each of the following papers. Several items warrant attention if you are reading an injury paper to assist you in assessing the value of the research work. These include the study design reported, the definition of injury used, what sources were used to identify the injuries from and what these sources may reflect regarding the severity of injury being studied. Nearly every study has one type of bias or another. The presence of bias is also discussed in each study.8Houseboat Carbon Monoxide Poisonings on Lake Powell• Study design• Definition of injury• Data Sources• Severity of Injury• Population• Bias• Findings• Case series• CO poisoning• NPS EMS transport records• medical attn or death• Lake Powell events• missing cases• outdoor exposuresThe first paper to examine is the MMWR paper on carbon monoxide poisonings noted at Lake Powell. This paper attempts to identify all CO poisoning events identified from the EMS records of the National Park Service from 1994-2000. It is thus a case series study design. The study was initiated because of case reports of CO poisoning death related to houseboats on the lake. The definition of injury used was based upon information in the transport records. Cases were defined as events with either (a) symptoms of CO poisoning and laboratory elevatedcarboxyhemoglobin values or (b) exposure to exhaust and symptoms.