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VCU STAT 210 - Lecture5

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Slide 1Example to think aboutTest 1Practice ProblemsAdditional Reading and ExamplesSlide 6B. Design of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsDesign of ExperimentsSlide 23Controlled ExperimentObservational StudiesObservational StudiesObservational StudiesExample 5Example 5Example 5Example 5Example 5Example 6Example 6Example 6Example 6Example 6Example 6Example 6Example 6Example 6Example 6Example 6Example 6STAT 210Lecture 5Design of ExperimentsSeptember 6, 2017Example to think aboutSuppose the population is all students enrolled in STAT 210 this semester. There are ten sections, and to select a sample of 40 students the following was done. 4 students were randomly selected from each of the 10 sections.What type of sampling procedure is this?Test 1Friday, September 8Questions from 1:00 to 1:10Test from 1:10 to 1:50 – papers due at 10:50!Covers chapters 1 and 2 (pages 1 – 42)Combination of multiple choice questions anda few written questions.Practice tests posted on Blackboard.Practice ProblemsPages 38 – 42Relevant problems: II.7, II.8, II.9, II.10Recommended problem: II.10Additional Reading and ExamplesPages 36 – 37Top HatB. Design of ExperimentsDesign and carry out an experiment that will allow us to evaluate the effect of a treatment or treatments.Example: Suppose we are interested in the effect of a new drug in reducing blood pressure.Design of Experiments1. Experimental Units: the subjects (or individuals or units) on which the measurements are made.Example: People medically identified as suffering from high blood pressure (diastolic pressure measurement of 90 or higher)Design of Experiments1. Experimental Units: the subjects (or individuals or units) on which the measurements are made.2. Treatment: an experimental condition applied to the experimental unitsExample: A new blood pressure medicine being evaluated, and the three leading blood pressure medicines that have been previously approved.Design of Experiments3. Response: the characteristic that is measured on each experimental unitExample: The diastolic blood pressure measurement of the patients in the study, or possibly the reduction in the diastolic blood pressure measurement before and after treatment.Design of Experiments3. Response: the characteristic that is measured on each experimental unit4. Comparison: we want to compare the results for one group (or treatment) with the results for another group (or treatment) or groups.Example: Compare the results for the new blood pressure drug to those of the three leading blood pressure medicines and no medication.Design of Experiments4. Comparison: we want to compare the results for one group (or treatment) with the results for another group (or treatment) or groups.5. Treatment Group(s): the group or groups of experimental units who receive the treatment(s)Example: The patients who get the new blood pressure drug are one treatment group, those who get each of the other three leading blood pressure drugs would be other treatment groups (for a total of 4).Design of Experiments5. Treatment Group: the group(s) of experimental units who receive the treatment(s)6. Control Group: a group of experimental units who do not receive the treatment, but instead receive either a fake treatment or nothing at all. Example: A group of patients who receive no active medication is the control group.A control group is not required if there are multiple treatment groups.Design of Experiments5. Treatment Group: the group of experimental units who receive the treatment6. Control Group: a group of experimental units who do not receive the treatment, but instead receive either an alternative treatment or nothing at all.7. Placebo: a fake treatment that is given to the experimentalunits in the control group to prevent them from knowing to which group they belong. This is important if there is not another treatment to compare the new treatment to.Design of Experiments7. Placebo: a fake treatment that is given to the experimentalunits in the control group to prevent them from knowing to which group they belong. This is important if there is not another treatment to compare the new treatment to.Example: If there is a group of people not receiving any medication (a control group) then they should receive a fake drug that looks similar to actual medication treatments.Design of Experiments8. Replication: Each group should contain more than one experimental unit, which should reduce chance variation in the results and reduce the effects of fluke occurrences.Example: Select 500 high blood pressure patients to participate. Randomly assign 100 of these patients to each of the five groups: 100 to the new blood pressure medicine group, 100 each to each of the three leading blood pressure drugs already approved, and 100 to the control group to receive the placebo but no active medicine.Design of Experiments9. Randomization: The experimental units used in the experiment should be randomly chosen, and they should be randomly assigned to the different groups. This can involve using the table of random digits.Example: Have each of the 500 patients draw a marble. Red - they receive the new blood pressure medicine Blue - they receive leading medicine A Yellow – they receive leading medicine B White – they receive leading medicine C Green – they receive the placeboDesign of Experiments9. Randomization: The experimental units used in the experiment should be randomly chosen, and they should be randomly assigned to the different groups. This can involve using the table of random digits.Example: The randomization can also be done by using the Table of Random Digits.Design of Experiments10. Blinding: The experimental units should not know to which group they have been assigned. This will hopefully reduce the occurrence of psychological effects, and is the reason for using placebos.Example: If the new and old blood pressure medications and the


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VCU STAT 210 - Lecture5

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