Experimental Studies (Lecture 8) - Zaroa University

Types of Epidemiologic Studies (Typology) Experimental studies Community Medicine & Epidemiology Dr. Sanabel Barakat Year 3 – semester 1 BDs., MSc., PhD., JDC. Week 8  ILOs...

Types of Epidemiologic Studies (Typology) Experimental studies Community Medicine & Epidemiology Dr. Sanabel Barakat Year 3 – semester 1 BDs., MSc., PhD., JDC. Week 8  ILOs Learn about experimental studies Discuss different types of experimental studies Calculate measures of risk 2  Classification of Epidemiological studies Epidemiological studies classification According to objective : Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies,) According to methodology: Observational Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies) Experimental (RCTs, Field trial, community trial) 3  Experimental studies Experimental studies are those in which the investigators control the exposure. Experimental studies generally ask the questions: - “What are the effects of this change of conditions?” - “What are the effects of this intervention?” 4  Experimental studies Intervention or experimentation involves attempting to change a variable in one or more groups of people. This could mean the elimination of a dietary factor thought to cause allergy, or testing a new treatment on a selected group of patients. The effects of an intervention are measured by comparing the outcome in the experimental group with that in a control group. 5  Experimental studies Since the interventions are strictly determined by the protocol, ethical considerations are of paramount importance in the design of these studies. For example, no patient should be denied appropriate treatment as a result of participation in an experiment, and the treatment being tested must be acceptable in the light of current knowledge. 6  Experimental studies Experimental studies differ from observational studies because the researcher is intervening in the studied population, controlling some exposure effect. These studies seek to test causal hypotheses about associations involving interventions of interest, such as the use of medications or vaccines, techniques, or preventive methods. When specific hypotheses of causal association between variables are tested, the study is said to be analytical. 7  Experimental studies Intervention studies allow the assessment of the effect in terms of the - Relative risk (RR) (incidence of disease in those exposed to intervention/disease incidence in non-exposed), - Absolute risk reduction (ARR) - Number needed to treat (NNT) Ref1 example for measures of association lecture ) 8  Experimental studies This type of study can take one of three forms: Randomized controlled trial RCTs Quasi experiments Cross over Split plot Factorial Field trial Community trial. 9  Clinical trials A clinical trial is a type of intervention study The starting point is the allocation of part of the participants (experimental group, test group or intervention group) to preventive or therapeutic procedures. Secondly, another part of participants (control group) receives the treatment as usual whose effectiveness is already known. In this sense, the primary objective of clinical trials is to evaluate end point treatment results, the cure of diseases, the survival of patients, or the reduction of sequelae. 10  Clinical trials RCT Quasi RCT Cross-over Split-plot Factorial 11  Randomized controlled trials Allocation The researcher allocates participants to one arm of trial (intervention Vs control). Randomized controlled trials (RCTs): When the intervention allocation criterion is at random, it is said that the study is randomized. Randomized studies are termed as controlled studies because of the random allocation of individuals in the group of exposed (intervention) and non-exposed (control) groups. This allocation criterion ensures that all the characteristics that may confound the interpretation of the results are distributed equally in each group. 12  Randomization Random allocation in a Randomized Control Trial (RCT) is the process of assigning participants to either the experimental group or the control group purely by chance. This ensures that each participant has an equal opportunity of being placed in any group, reducing bias and ensuring that the groups are comparable in all respects except for the intervention being tested. 13 Randomization methods Dice Coin Computer generated list Sealed envelopes /bottles 14 Randomization types/ designs Simple Cluster Stratified Block Assignment: find definitions 15  RCT 16  Randomization Because the participants are randomly assigned, the characteristics between the two groups should be balanced, enabling researchers to attribute any differences in outcome to the study intervention. Since researchers can be confident that any differences between the control and treatment groups are due solely to the effects of the treatments, scientists view RCTs as the gold standard for clinical trials 17  Study groups 1- Intervention, test or experimental group: participants receive the intervention 2- Control group: participants who do not receive any treatment or intervention serve as a comparison group. May matched as closely as possible to the experimental group, including age, gender, social class, ethnicity, etc. Receive placebo, reference treatment, no treatment, gold standard 18  RCT Study groups Because the participants are randomly assigned, the characteristics between the two groups should be balanced, enabling researchers to attribute any differences in outcome to the study intervention. 19  Intervention studies allow the assessment of the effect in terms of: The relative risk (RR) (incidence of disease in those exposed to intervention/disease incidence in non-exposed) Absolute risk reduction (ARR) (incidence of disease in non-exposed – incidence of disease in the exposed * 100 in %), Relative risk reduction(RRR)= (1 – RR * 100) The number needed to treat (NNT) = (1/ARR). This means the number of people needed to be exposed to the intervention to avoid a case of the disease 20  Test Control Total Effect a b a+b No effect c d c+d a+c b+d a+b+c+d 21 22  RCTs provide a good illustration of the difficulties of epidemiological studies to present both internal and external validity. They have strong internal validity, due to the many methodological requirements for their accomplishment. However, these studies are often subject to external validity restrictions, depending on the specific characteristics of their samples. Most of RCTs are expensive, and only individuals who meet various selection requirements are researched, which prevents the results from being extrapolated to the general population  Quasi-clinical trials Allocation Quasi-experiment, Quasi-clinical trial. When allocation of intervention among groups is not random. If subject allocation is based on date, weekday, odd or even numbers… ect. Compared to RCTs They are easier They have poorer internal validity 24 Cross-over The same person (i.e., the case)receives two (or more) types of exposures in sequence. After the first exposure/treatment is delivered, outcomes are noted, and the person is allowed an exposure-free period called the “washout period” when the exposure and its effect are allowed to be completely eliminated. Thereafter, the subsequent exposure is applied and outcomes are noted. The results of the two exposures are then compared. 25  Cross-over The key advantage of such a design is that the same person acts as his or her own control or comparison group, thereby effectively matching for all person-related factors. 26  Cross-over The disadvantage is the possibility that the first exposure may in some way influence the responses from the second factor, which may or may not be independent of the adequacy of the washout factor (the effects of the first exposure persist for a long time), which is called a carryover effect from the first exposure. Carryover effects may impact the outcomes from the second exposure (e.g. educational intervention) 27  Split plot design , split body or split mouth model Uses one side of the person for test and the other side as a control/ comparison. Useful when the investigator wants to control for factors that are very difficult to control, such as the genotype, salivary flow rate, and immunological response among others. The control is exactly matched to the test for all measured and unmeasured sources of variation 28  For example, in a person with generalized periodontitis, one side (left or right) may be Split mouth model treated with a surgical treatment and the results may be compared with the other side whichis treated with medication intervention 29  Factorial designs Categorize interventions by two (or more) independent factors and randomize participants in the resulting groups. The number of factors can be many. These designs are usually identified by the number of factors and their levels being examined. 30  Factorial designs 31  Field trial Field trials, in contrast to clinical trials, involve people who are disease-free but presumed to be at risk; data collection takes place "in the field", usually among non-institutionalized people in the general population. Since the subjects are disease-free and the purpose is to prevent the occurrence of diseases that may occur with relatively low frequency, field trials are often huge undertakings involving major logistic and financial considerations. Example , a field trial of a new vaccine against virus X 32  Community interventions In this type of experimental study, the unit of analysis and allocation for intervention is the community, a town, or a region, and not individuals. Used to test the effectiveness of an intervention, which often cannot be tested through random studies. The fluoridation of public water supply is an excel lent example of this type of study. Or used for diseases that have their origins in social conditions, which in turn can most easily be influenced by intervention directed at group behaviour as well as at individuals. 33 34  Thank you 35