Experimental Studies Lecture 2, Chapter 6 PDF

Experimental Studies Dr. Muhammad Ahmed Alshyyab Lecture 2 Chapter 6 LEARNING OBJECTIVES: In this lecture, you will be able to demonstrate the following key massages: Epidemiologists must consider all sources of errors, and strive to reduce them....

Experimental Studies Dr. Muhammad Ahmed Alshyyab Lecture 2 Chapter 6 LEARNING OBJECTIVES: In this lecture, you will be able to demonstrate the following key massages: Epidemiologists must consider all sources of errors, and strive to reduce them. Epidemiologists devote much attention to minimizing errors and assessing the impact of errors that can not be eliminated Understanding techniques that epidemiologists should use to minimize Potential errors in epidemiological trial studies The control group Confounding Recruitment and eligibility criteria Sample size requirements The control group Referent groups in experimental studies are properly called control groups. Without the referent rate provided by the control group, it would often be impossible to determine the extent to which the rate in the treatment group reflected the effect of the treatment or the natural history of the disease. The effects of an exposure can only be judged in comparison to what would happen in its absence Placebo effect The placebo effect refers to perceived improvements following treatment with a pharmacologically inert substance (‘‘placebo’’) such as a sugar pill or saline injection. This effect has been ascribed to a positive belief in the treatment and the perception of being cared for. Despite popular belief, placebos have no real effect. Prior studies showing placebo effects were unsound. The Hawthorne Effect The Hawthorne effect refers to the tendency of subjects to alter their behaviour in a way that is favourable to the results of the study. Continual improvements in worker performance were observed over the course of the study no matter the nature of the intervention. The people will act differently if they know they are being observed. It is also known as Observer effect. John Henry effect A comparable attention bias effect is observed in subjects in health studies. A counter John Henry effect may occur when a control group getting no intervention compares themselves to the treatment group and responds by actively working harder to overcome the ‘‘disadvantage’’ of being in the control group. Minimizing control group effect on the study results Blinding (masking) the study participants and investigators about the treatment being received offers just such protection. The simplest way is use a parallel design in which the experience of the treatment group and control group are compared concurrently: An Example for the Importance of concurrent control group (MRFIT) Multiple Risk Factor Intervention Trial (1982) Exposure: Health education vs. no special intervention (randomly assigned) Outcome: CVD Treatment group experienced dramatic declines in CVD rates But so did the control group Explanation: – People were changing behavior in the 1970s – Rates were declining in all groups If there were no control group were present the intervention would unjustifiably have been declared a success