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Explaining the parts of an experiment A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective.

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Presentation on theme: "Explaining the parts of an experiment A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective."— Presentation transcript:

1 Explaining the parts of an experiment A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked

2 What is the population of interest? (what group are you interested in) What is the parameter of interest? (what do you want to know)

3 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked What is the response variable that will explain your parameter of interest? (what is it that you are measuring and comparing)

4 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked What are the treatments and factor levels for each? (what will the different groups get and how much)

5 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked What are the experimental units or subjects? (who / what will you be experimenting on)

6 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked 4 Principles of a Design? 1- Control – how will you control sources of variability that could affect your response variable? (what will you do to make everything the same)

7 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked 4 Principles of a Design? 2- Random Assignment – how will you place experimental units/ subjects in to treatment groups (what is your sampling method – SRS, Stratified, Systematic, etc)

8 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked 4 Principles of a Design? 3- Replicate – multiple subjects in each treatment (larger the sample the better the results)

9 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked 4 Principles of a Design? 4- Blocking – group units/subjects by common characteristic to remove confounding variables (by gender, age, location, etc – not always necessary)

10 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked Units / Subjects RANDOMIZERANDOMIZE TREATMENT #1 Factor and level TREATMENT #2 Factor and level TREATMENT #3 Factor and level Collect Response Variable Compare Results Blinded? Placebo Effect?

11 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked Units / Subjects Block #1 Common Characteristic Block #2 Common Characteristic TREATMENT #1 Factor and level TREATMENT #2 Factor and level TREATMENT #1 Factor and level TREATMENT #2 Factor and level RANDOMIZERANDOMIZE Collect Response Variable Collect Response Variable Compare Results

12 A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked Scope and Nature of Conclusion (what are the results and who do they apply to?)

13 Draw out the experiment BeginConclusion A dog food company wants to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They have found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply some owners of each size of dog with one of the two foods. The owners have agreed not to feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked

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15 Experiment – manipulate factor levels to create treatments, compare response variables to determine causation Population and parameter of interest: who/what will you experiment on and what will you be measuring and comparing Factor: variable levels are manipulated by the experiment Level: specific values that are chosen for a factor – levels of the factor Treatments: intervention applied to randomly assigned experimental units Principles of experimental design: 1- Control – all variables that may have an effect but not being tested 2- Randomize – subject to treatments, even out effects cant control 3- Replicate – over many subjects as possible, or different groups if groups not representative of population 4- Block – reduce effects of common characteristics of subjects that cant be controlled Lurking variables: {observations} an apparent association between variables is really a common response to a third variable - Avoided in experiments by randomization Confounding variable: {experiments} response is partially attributable to uncontrolled variables. The variables vary together making it impossible to determine which variable is the cause


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