A medical researcher obtains a sample of adults suffering from diabetes. She randomly assigns 95 people to a treatment group and 95 to a placebo group. The treatment group receives medication over a period of three months and the placebo group receives a placebo. After the three months the patients' symptoms are evaluated. Is it observational study or experiment?

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Types of Bias

Statistics is the study of data collection, organization, analysis, interpretation, and presentation. Statistical bias is a characteristic of a statistical technique or its findings in which the expected value deviates from the actual root quantitative parameter being estimated. According to the actual definition of bias, it refers to the tendency of a statistic to overestimate or underestimate a parameter.