assures that all participants have an equal chance of being assigned to any condition.
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Random sampling is the sample group of subjects that are selected by chance, without bias. Random assignment is when each subject of the sample has an equal chance of being in either the experimental or control group of an experiment.
Random sampling in surveys takes a randomly selected smaller group from a larger population (so the smaller group is a sample of the larger group). Random assignment separates (randomly) this chosen small group further, into a control group and a treatment group for experiments. For instance, in research surveys: if a group of sick people are asked about their symptoms, they are placed in separate categories of similar symptoms, and then are diagnosed with particular illnesses. Further, in random assignment: if one medicine is given to the group, and it only helps certain symptoms, then a cure has been found for only those particular illnesses, and not the others. You see, random sampling asks certain questions of subjects and gets various responses, whereas, random assignment applies certain principles to subjects and gets various responses. Both ways lead to results which render solutions to problems. If not, further experimentation needs to be made.
Without random assignment there is a danger of systematic error - or bias - entering into the results. Statistical theory depends on the errors being random and independent error and that is no longer the case without random assignment. In fact, statistical experiments are often "double-blind": even the observer does not know which individual is in which group. This is to prevent unconscious or subconscious messages to affect the outcome (placebo effects).
Three basic research designs are experimental, correlational, and quasi-experimental.Experimental designs have random assignment to conditions. Correlational designs define the relationship between two measured values. Quasi-experimental designs have participants grouped on a variable that isn't manipulated.
What is a type of research that uses focus groups or small studies to get a "feel" for the problem.