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Chapter 1 – Section 5- Learning objectives
- Define designed experiment
- Understand the steps in designing an experiment
- Understand the completely randomized design
- Understand the matched-pairs design

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Chapter 1 – Section 5- Learning objectives
- Define designed experiment
- Understand the steps in designing an experiment
- Understand the completely randomized design
- Understand the matched-pairs design

Chapter 1 – Section 5

- Data can be collected in two main ways
- Through sample surveys
- Through designed experiments

- Sample surveys lead to observational studies
- Designed experiments enable researchers to control variables, leading to additional conclusions

Chapter 1 – Section 5

- A designedexperiment is a controlled study
- The purpose of designed experiments is to control as many factors as possible to isolate the effects of a particular factor
- Designed experiments must be carefully set up to achieve their purposes

Chapter 1 – Section 5

- Some variables in a designed experiment are controlled, those are the explanatoryvariables
- These variables are also sometimes called the factors
- Factors
- Are part of a controlled environment
- Has values that can be changed by the researcher
- Are considered as possible causes

Chapter 1 – Section 5

- Examples of factors are
- The dosage of a drug in a medical experiment
- The type of teaching method in an education experiment
- One drug by itself compared to that drug used in conjunction with another

Chapter 1 – Section 5

- The designed experiment analyzes the affects of the factors on the responsevariable
- Response variables
- Are not part of a controlled environment
- Has values that are measured by the researcher
- Measure the effects

Chapter 1 – Section 5

- Examples of response variables are
- The blood pressures of the patients
- The test scores for a class
- The sizes of a cancerous tumor for patients

Chapter 1 – Section 5

- A treatment is a combination of the values of the factors
- Examples of treatments
- Giving one medication to one group of patients and a different medication to another
- Using one type of fertilizer on a set of plots of corn and a different type of fertilizer on a different set of plots
- Playing country music to one group of mice and rap music to another

Chapter 1 – Section 5

- The treatment is applied to experimentalunits (people, plants, materials, other objects, …)
- When the experimental units are people, we refer to them as subjects
- Subjects in an experiment correspond to individuals in a survey

Chapter 1 – Section 5

- An example of a designed experiment is to determine whether a new drug, Drug N, is more effective at treating high blood pressure than the existing drug, Drug E
- Patients with high blood pressure are given either Drug N or Drug E
- The blood pressures are measured one month later

Chapter 1 – Section 5

- For this experiment
- Factor – the type of drug
- Response variable – blood pressure
- Treatment – given Drug N or Drug E
- Experimental units / subjects – the patients

- For this experiment
- Factor – the type of drug
- Response variable – blood pressure
- Treatment – given Drug N or Drug E
- Experimental units / subjects – the patients

- If patients given Drug N have significantly lower blood pressures than patients given Drug E, we would wish to conclude that Drug N is more effective

Chapter 1 – Section 5

- Changes in behavior of subjects

- Changes in behavior of subjects
- For an experiment comparing a new drug to no treatment at all
- If the subject knows that he or she is given a drug, he or she may feel better (the placebo effect)

- Changes in behavior of subjects
- For an experiment comparing a new drug to no treatment at all
- If the subject knows that he or she is given a drug, he or she may feel better (the placebo effect)

- For an experiment comparing a new drug to an existing drug
- If the subject knows which drug he or she is given, that may change his or her behavior

Chapter 1 – Section 5

- To avoid the effects of subject behavior
- Subjects not given any medication are often given a placebo such as a sugar tablet
- The subjects will not know which treatment they get

- To avoid the effects of subject behavior
- Subjects not given any medication are often given a placebo such as a sugar tablet
- The subjects will not know which treatment they get

- To avoid the effects of researcher behavior
- The researchers are not told which drug they are administering

- To avoid the effects of subject behavior
- Subjects not given any medication are often given a placebo such as a sugar tablet
- The subjects will not know which treatment they get

- To avoid the effects of researcher behavior
- The researchers are not told which drug they are administering

- When both the subjects and the researchers do not know which treatment, this is called double-blind

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Chapter 1 – Section 5- Learning objectives
- Define designed experiment
- Understand the steps in designing an experiment
- Understand the completely randomized design
- Understand the matched-pairs design

Chapter 1 – Section 5

- Conducting an experiment involves considerable planning

- Conducting an experiment involves considerable planning
- Planning steps

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors
- Determine the number of experimental units

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors
- Determine the number of experimental units
- Determine the level of each factor

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors
- Determine the number of experimental units
- Determine the level of each factor

- Implementation steps

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors
- Determine the number of experimental units
- Determine the level of each factor

- Implementation steps
- Conduct the experiment

- Conducting an experiment involves considerable planning
- Planning steps
- Identify the problem
- Determine the factors
- Determine the number of experimental units
- Determine the level of each factor

- Implementation steps
- Conduct the experiment
- Test the claim

Chapter 1 – Section 5

- Identify the problem
- The first step in planning an experiment (or in most any project at all) is to identify the problem
- The identification would include
- The general purpose of the experiment
- The response variable
- The population

- This is also referred to as the claim

Chapter 1 – Section 5

- Determine the factors
- The second step in planning an experiment is to determine the factors to be studied
- The factors could be identified
- By subject matter experts
- By the purpose of the experiment
- Using results from previous studies

- Factors must be identified as either fixed, controlled, or uncontrolled

Chapter 1 – Section 5

- Determine the number of experimental units
- In general, the more the experiment units, the more effective the experiment
- The number of experimental units
- Could be limited by time
- Could be limited by money

- There are techniques to calculate the number of experimental units (to be covered later)

- Determine the level of each factor
- Three ways to deal with the factors
- Control – fix the levels at a constant level (for factors not of interest)

- Determine the level of each factor
- Three ways to deal with the factors
- Control – fix the levels at a constant level (for factors not of interest)
- Manipulate – set the levels at predetermined levels (for factors of interest)

- Determine the level of each factor
- Three ways to deal with the factors
- Control – fix the levels at a constant level (for factors not of interest)
- Manipulate – set the levels at predetermined levels (for factors of interest)
- Randomize – randomize the experimental units (for uncontrolled factors not of interest)

- Determine the level of each factor
- Three ways to deal with the factors
- Control – fix the levels at a constant level (for factors not of interest)
- Manipulate – set the levels at predetermined levels (for factors of interest)
- Randomize – randomize the experimental units (for uncontrolled factors not of interest)

- Randomization decreases the effects of uncontrolled factors, even ones not identified

- Determine the level of each factor
- Three ways to deal with the factors

Chapter 1 – Section 5

- Conduct the experiment
- The subjects are assigned at random to the treatments
- When a treatment is applied to more than one experimental unit, this is called replication
- Replication is useful for accuracy, to further decrease the effects of uncontrolled factors

- Collect and process the data

Chapter 1 – Section 5

- Test the claim
- This is inferential statistics
- Techniques of inferential statistics are studied in chapters 9 through 14

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Chapter 1 – Section 5- Learning objectives
- Define designed experiment
- Understand the steps in designing an experiment
- Understand the completely randomized design
- Understand the matched-pairs design

Chapter 1 – Section 5

- A completelyrandomizeddesignis when each experimental unit is assigned to a treatment completely at random

- A completelyrandomizeddesignis when each experimental unit is assigned to a treatment completely at random
- An example
- A farmer wants to test the effects of a fertilizer
- We choose a set of plants to receive the treatment
- We randomly assign plants to receive different levels of fertilizer

- A completelyrandomizeddesignis when each experimental unit is assigned to a treatment completely at random
- An example
- A farmer wants to test the effects of a fertilizer
- We choose a set of plants to receive the treatment
- We randomly assign plants to receive different levels of fertilizer

- This has similarities to completely random sampling

Chapter 1 – Section 5

- We control as many factors as we can
- Amount of watering
- Method of tilling
- Soil acidity

- We control as many factors as we can
- Amount of watering
- Method of tilling
- Soil acidity

- Randomization decreases the effects of uncontrolled factors
- Rainfall
- Sunlight
- Temperature

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Chapter 1 – Section 5- Learning objectives
- Define designed experiment
- Understand the steps in designing an experiment
- Understand the completely randomized design
- Understand the matched-pairs design
- Understand the randomized block design

Chapter 1 – Section 5

- A matched-pairdesignis when the experimental units are paired up and each of the pair is assigned to a different treatment

- A matched-pairdesignis when the experimental units are paired up and each of the pair is assigned to a different treatment
- A matched pair design requires
- Units that are paired (twins, the same person before and after the treatment, …)
- Only two levels of treatment (one for each of the pair)

- A matched-pairdesignis when the experimental units are paired up and each of the pair is assigned to a different treatment
- A matched pair design requires
- Units that are paired (twins, the same person before and after the treatment, …)
- Only two levels of treatment (one for each of the pair)

- An example
- A subject before receiving the medication
- The same subject after receiving the medication

Chapter 1 – Section 5

- Test whether students learn better while listening to music or not
- Match students by IQ and gender (to control those factors)
- Randomly choose one of each pair (to decrease the effects of other uncontrolled factors
- Assign that one to a quiet room and the other to a room with music (the treatment)
- Administer the test and analyze the test scores

Chapter 1 – Section 5

- An example
- We are testing the effects of treatments A, B, and C on soybean plants
- Assume that group 1 is treated with A and group 2 is treated with B
- Assume that Chemgro plants have higher yields than Pioneer plants
- Assume that group 1 has more Chemgro plants (happens because of randomization) than group 2

Chapter 1 – Section 5

- If group 1 (treatment A) has higher yields than group 2 (treatment B)
- Is this because treatment A is more effective than B?
- Is this because there are more Chemgro plants in group 1?

- If group 1 (treatment A) has higher yields than group 2 (treatment B)
- Is this because treatment A is more effective than B?
- Is this because there are more Chemgro plants in group 1?

- It is not possible to distinguish
- The effects of Treatment A versus B
- The effects of Chemgro versus Pioneer

- If group 1 (treatment A) has higher yields than group 2 (treatment B)
- Is this because treatment A is more effective than B?
- Is this because there are more Chemgro plants in group 1?

- It is not possible to distinguish
- The effects of Treatment A versus B
- The effects of Chemgro versus Pioneer

- When two effects cannot be distinguished, this is called confounding

Summary: Chapter 1 – Section 5

- The planning for designed experiments is crucial to the success of the experiment
- A double-blind implementation of experiments reduces the amount of changes in behavior
- There are different good methods for assigning treatments to experimental units
- Completely random
- Matched-pairs
- Randomized blocks

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