2.Bio7.2008.Ch8.Ch1.1pg - Today Announcements the waitlist...

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Today: " Announcements: the waitlist, hints on the current homework " Chapter 8: Experiments, with a couple of worked problems interspersed " Chapter 1: Descriptive statistics " A suggestion for people feeling lost. . " More worked problems if I have time Experiments Chapter 8 1. Terminology ! The individuals in an experiment are the experimental units . If they are human, we call them subjects . ( suckers ??? ) ! In an experiment we do something to the subject and measure the response. The “something” is the explanatory variable , also called a factor . " The factor may be the administration of a drug. " One group of people may be placed on a diet (factor #1) and exercise (factor #2) program for six months (the combination of factors is called a treatment ). Their blood pressure (the response variable ) would be compared with that of people who did not diet or exercise. ! If the experiment involves giving two different doses of a drug, we say that we are testing two levels of the factor. ! A response to a treatment is statistically significant if it is larger than you would expect by chance (due to random variation among the subjects). We will learn how to determine this later. 2. Comparative experiments Experiments are comparative in nature: we compare the response to a treatment versus to: " another treatment, " no treatment (the “control”) " a placebo " or any combination of the above A control is a situation when no treatment is administered. It serves as a reference mark for an actual treatment (ex. a group of subject does not receive any drug or pill of any kind). In some experiments a placebo is used. Subjects -> Treatment -> Response
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About the placebo effect The “placebo effect” is an improvement in health due not to any treatment but only to the patient's belief that he or she will improve. " The 'placebo effect' is not understood but it is believed to have therapeutic results on up to a whopping 35% of patients. " It can sometimes ease the symptoms of a variety of ills, from asthma to pain to high blood pressure, and even to heart attacks. " An opposite, or “negative placebo effect,” has been observed when patients believe their health will get worse. " The most famous and maybe most powerful placebo is a kiss and a hug. Completely Randomized Experimental Designs: Individuals are randomly assigned to groups, then the groups are randomly assigned to treatments. We randomize to minimize confounding factors. For instance, in an experiment testing drugs and diet to control cholesterol, if you let men choose their diet/salt treatment, you would confound the experiment based on their food preferences, which probably has already affected their blood pressure. 3. Completely randomized designs In a block or stratified design , subjects are divided into groups , or blocks , prior to experiment to test hypotheses about differences between the groups.
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2.Bio7.2008.Ch8.Ch1.1pg - Today Announcements the waitlist...

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