Week 6.pdf

Research designs- III Dr.Fawaz Pullishery Dentistry Program Batterjee Medical College Experimental Studies These studies involve some actions, intervention or manipulation such as deliberate application or withdrawal of the suspected cause or changing one variable in...

Research designs- III Dr.Fawaz Pullishery Dentistry Program Batterjee Medical College Experimental Studies These studies involve some actions, intervention or manipulation such as deliberate application or withdrawal of the suspected cause or changing one variable in the causative chain in the experimental group while making no change in the control group and observing and comparing the outcome of the experiment in both the groups. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Aims: To provide "scientific proof" of etiological factors. a method of measuring the effectiveness and efficiency of health services. These studies can be conducted on animals or human beings. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Historically important human experiments By James Lind on soldiers for scurvy; Edward Jenner’s for cowpox; Goldberg’s on pellagra etc W.H.O in 1980 has laid down a strict code of practice in connection with the human trials. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Types Of Experimental Studies 2 types Randomized Non-randomized control trials control trials Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Randomized Control Trials An assessment method of an epidemiologic experiment for new programs or therapies. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Basic Steps - Randomized Control Trials 1. Drawing up a protocol 2. Selecting reference and experimental populations 3. Randomizations 4. Manipulation / Intervention 5. Follow -up 6. Assessment of outcome Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College 1. The Protocol An essential feature of any RCT Every trial is conducted under a strict protocol. Specifies the aims and objectives of the study, questions to be answered, and criteria for selection of the study and control groups, sample size. Treatment to be applied etc. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  Once evolved; it should be strictly adhered to throughout the study. Protocol aims at— Preventing bias Reduce the source of error It is important that the final version of the protocol should be agreed upon by all the concerned before the trial begins Pilot study – also called as feasibility study. it is done on a small sample size to check whether the study is feasible under certain conditions, environment etc…. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Selecting The Reference And Experimental Populations Reference /Target Population It is the population to which the findings of the trial, if found successful, are expected to be applicable. E.g. population of the whole city, school children, industrial workers etc Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Experimental /Study Population It is derived from the reference population. Ideally should be randomly chosen from the reference population. It is also important to choose a stable population whose co- operation is assured to avoid losses to follow -up. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College The participants should fulfill the following criteria: - They must give informed consent Should be representative of the population Should be qualified or eligible for the trial. [i.e. fully susceptible to the disease under study Anemia, whooping cough, composite. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Randomization “Heart" of a control trial. It is the statistical procedure by which the participants are randomly allocated into groups usually called the "study" and "control" groups. It is an attempt to eliminate "bias" and allow for comparability. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  Randomization eliminates “selection bias and confounding bias” Randomization is done only after the participant has entered the study and it can be done by using table of random numbers or lot method or. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Blinding Blinding is a measure in randomized controlled trials (RCT) to reduce detection and performance bias. Single blinding- Patient does not which group he belongs to. Also called “break the blind”. Double blinding: Both patient and doctor do not know which group the patient belongs to : “ask another doctor” Double blinding is done to exclude assessment bias and to exclude the suspicion of assessment bias. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  Triple blinding: Patient (participants) , doctor and the person who analyze the results are blinded. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  Manipulation After forming the study and control group manipulation in done by deliberate application or withdrawal or reduction of suspected causal factor. it creates an independent variable (e.g.- drug, vaccine) whose effect is the determined by final outcome which constitute dependent variable (e.g. incidence of disease, survival time, recovery period). Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Follow up it implies examination and control group subjects at different interval of time. losses of follow due to inevitable(death, migration, loss of interest). It is called attrition. If it substantial , it should be minimized. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Assessment It is assessment of trial in terms of positive and negative result. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Types of randomized Control trials Clinical trials Preventive trials Risk factor trials Cessation experiments Evaluation of health services Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Clinical Trials The evaluation of the therapeutic agents, mainly drugs. Ethical, administrative and technical problems are evolved while conducting the clinical trials. They are a powerful tool and should be carried out before any new therapy, procedure or service is introduced. Teeth whitening toothpaste, powered toothbrush. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Preventive Trials To prevent or eliminate disease on an experimental basis. The most commonly occurring trials are that of vaccines and chemo prophylactic drugs. E.g. Trial of whooping cough vaccines. Caries vaccine. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Risk Factor Trials The investigator intervenes to interrupt the usual sequence in the development of disease for those individuals who have “risk factor” for developing the disease. Can be either “single factor” or “multi factor”. Example: The WHO promoted trial on primary prevention of coronary heart disease was largest preventive trial. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Cessation Experiments An attempt is made to evaluate the termination of a habit, which is considered to be causally related to a disease. If it results in significant reduction of the disease, the hypothesis of cause is strengthened Smoking, tobacco. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Evaluation Of Health Services To assess the effectiveness and efficiency. Since resources are limited and priorities must be set for the implementation of a large number of activities. e.g. T.B. regimen {domiciliary} Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Non-randomized Trials (QUASSI EXPERIMENTAL) Due to ethnical or administrative problems, it is not always possible to carry out randomized control trials on humans. Also called as quassi experimental study Some preventive measures can be applied only to groups or on a community. If the disease frequency is low and the natural history long, then follow-up is a major problem. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Types of Bias Selection bias occurs where experimental subjects or specimens are divided into different intervention groups. Allocation concealment is the practice of protecting the randomization sequence from prior knowledge to the participants or researchers. This minimizes selection bias. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Assessment bias Assessment bias in a clinical trial occurs if bias in the assessment of the outcome exists. It is also called ascertainment bias, diagnostic bias, or detection bias. A major cause of assessment bias is lack of blinding (triple blinding). Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  References 1. ParK K. Text book of Preventive and Social Medicine, 18th ed. Jabalpur: Banarsidas Bhanot Publishers.2005. 2. Beaglehole R, Bonita R, Kjellstrom T. Basic Epidemiology, 1st ed. WHO publication. 3. Sober Peter. Essentials of Preventive and Community Dentistry, 2nd ed. New Delhi : Arya Publishing House, 2003 4. Health Research Methodology. 1993. WHO publication. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College  5. Gordis L. Epidemiology. 3rd ed. Pennyslavania : Saunders, 2004 6. Gupta MC, Mahajan B. Textbook of preventive and social medicine. 3rd ed. New Delhi : Jaypee Brothers. 2003. 7. Abrahmson JH, Abrahmson ZH. Survey Methods in Community Medicine. 5th edition. Edinburgh:Churchill Livingstone ; 1999. Dr. Fawaz P'Shery, Dentistry program, Batterjee Medical College Thank You