#CONTROL GROUP TRIAL#

Can be done when a pretest is not possible As this design does not have any pretest, it will not be subject to this bias. So a study involving a pretest may be measuring the effect of the intervention along with this test-retest effect (a.k.a. a participant taking the test the second time may be more prepared to the type of questions asked, etc.a physician might be influenced by a previous diagnosis or opinion made on a patient.Not affected by reactions to pretestingĪn additional source of bias may be present when posttest results can be influenced by the results of a pretest. In these designs, the participant’s ID, name or phone number will be recorded in a database which may interfere with some type of studies where the participant’s anonymity is critical. When subjects are measured before and after the intervention, some sort of system should be installed in order to know which measurement corresponds to which participant. Can be used when participants’ anonymity must be kept The simultaneity in measuring both groups controls factors that change with time (as these may also affect the outcome and bias the study).ģ.The use of 1 measurement only controls factors related to the instruments used to measure the outcome (since the device is only used once to measure the outcome, we won’t have to deal with changes that can happen to the device or to the quality of measurements from 1 measurement to the next).adjusts for the effects of events that can happen at the same time as the intervention and can influence the outcome, therefore becoming a rival hypothesis and a potential source of bias). The use of a control group controls history (i.e.This is an advantage over static-group comparison where assignment is not done at random, so the initial difference in the characteristics of both groups can be an important factor influencing the outcome of the study and therefore an important source of bias. As long as we are assigning participants at random, we won’t be subject to selection bias and we will obtain comparable groups. Note that these groups are not expected to be perfectly equal, in fact they don’t need to be. This is very important because when the 2 groups are equal, any difference in the outcome measured will be attributed only to the intervention and not to the initial difference between the groups. The treatment and control groups are equivalent at baseline Advantages of the posttest-only control group design 1.

Also, if we remove the random assignment component from this design (and let participants get assigned to groups according to their choosing or that of the researcher), we get the static-group comparison design which is a type of quasi-experiment.

#CONTROL GROUP TRIAL#

Note that this design differs from the pretest-posttest randomized controlled trial by having no measurements taken before the intervention.

Control group