Statistics 115: 1.6 The Design of Experiments

A school psychologist wants to test the effectiveness of a new method of teaching FrenchFrench. She recruits 100100 firstfirst​-grade students and randomly divides them into two groups. Group 1 is taught by means of the new​ method, while group 2 is taught by traditional methods. The same teacher is assigned to teach both groups. At the end of the​ year, an achievement test​ (graded on a scale from​ 1-10) is administered and the results of the two groups are compared. Complete parts​ (a) through​ (i) below. (a) What is the response variable in this​ experiment? (b) Is the response variable qualitative or​ quantitative? (c) Which of the following explanatory variables is​ manipulated? ​(d) What are the​ treatments? How many treatments are​ there? ​(e) How are the factors that are not controlled dealt​ with? ​(f) Which group serves as the control​ group? ​(g) What type of experimental design is​ this? ​(h) Identify the subjects.

(a) The scores on the achievement tests of both group 1 and group 2 (b) The response variable is quantitative because it is a measurement (c) method of teaching (d) The treatments are the new teaching method and the traditional teaching method. There are 2 treatments. (e)Random assignment (f)Group 2 serves as the control group because this group corresponds to the standard method that will be compared to the other method. (g) Completely randomized design (h) the 100 students

A researcher has decided to test the effectivness of a drug meant to reduce high cholesterol through a completely randomized design. She has obtained 9 volunteers with high​ cholesterol: Amanda,​ Brian, Christine,​ David, Emily,​ Fred, George,​ Heather, and Ivan. Number the volunteers 1 through​ 9, alphabetically. Use the thirdthird row of digits in the random number table below to randomly assign 3 of the volunteers to the experimental group​ (ignore zeros). The remaining volunteers will go into the control group. List the individuals in each group. Row 1 72359 32760 69373 52413 Row 2 67278 38419 38199 57498 Row 3 59644 14233 02661 53972 What are the numbers of the three volunteers​ selected? List the three indivduals assigned to the experimental group. Choose the correct answer below. List the remaining indivduals assigned to the control group.

--5, 9, 6 --Emily, Ivan, Fred --Brian, Heather, Amanda, David, George, Christin

To help assess student learning in her reform calculusreform calculus ​courses, a calculusa calculus professor at a universityuniversity implemented​ pre- and​ post-tests for her reform calculusreform calculus students. A​ knowledge-gained score was obtained by taking the difference of the two test scores. What type of experimental design is this? What is the response variable in this experiment? What is the treatment?

--Matched pair --Difference in test scores --calculus course

Placebo

A second method for defining the control group. A placebo is an innocuous medication, such as a sugar tablet, that looks, tastes, and smells like the experimental medication.

Suppose you are interested in comparing brand A interior enamel paint to brand B interior enamel paint. Design an experiment to determine which paint is better for painting ceilings Choose the best design for this experiment.

Matched-pairs design because experimental units are paired up and there are only two levels of treatment.

generally, the goal of an experiment is to determine the effect that treatment will have on the response variable

True: an experiment is defined as a controlled study conducted to determine the effect varying one or more factors has on a response variable, and any combination of the values of the factors is called a treatment. Therefore, the goal of an experiment is to determine the effect that the treatment will have on the response variable.

experiment

a controlled study conducted to determine the effect varying one or more explanatory variables or factors has on a response variable. Any combination of the values of the factors is called a treatment.

Researchers wanted to test the effectiveness of a new drug therapy for treating patients with dementia.dementia. To do​ this, they identified 150150 patients with a diagnosis of dementia.dementia. Patients were randomly assigned to one of three treatment groups. Fifty patients were randomly assigned to receive the new drug​ therapy, another 50 received the older drug​ therapy, and the final 50 received a placebo therapy. To measure the effectiveness of the​ treatment, researchers scored each patient on a standardized rating scale for dementia. After collecting and comparing the scores for the three treatment​ groups, the researchers concluded that the new drug therapy is significantly more effective than both the older drug therapy and the placebo therapy in the treatment of dementia. Complete parts​ (a) through​ (f). a. What type of experimental design is​ this? (b) What is the population being​ studied? ​(c) What is the response variable in this​ study? d) What are the​ treatment(s)? (e) Identify the experimental units. Choose the correct answer below.

a. Completely randomized design b.All patients with a diagnosis of dementia c.The score on the standardized rating scale for dementia d.The new drug​ therapy, the older drug​ therapy, and the placebo therapy e.The 150 patients with a diagnosis of dementia f.

completely randomized design

each experimental unit is randomly assigned to a treatment

A professor wanted to compare two types of teaching styles. One type is by tutorials and the other is giving a lecture. It is a common belief that tutorials result in better retention. This belief is tested by having 10 students learn a topic by each method and then having them take a test on their knowledge of the material that was covered. A coin flip was used to determine which type of teaching method a student would be given first. Results indicated that there was no difference in the two types of presentation . Complete parts​ (a) through​ (f) below. ​(a) What type of experimental design is​ this? ​(b) What is the response variable in this​ study? ​(c) What is the factor that is set to predetermined​ levels? What is the​ treatment? (d) Identify the experimental units. Choose the correct answer below. (e) Why is a coin used to decide the teaching method a student would be given firstteaching method a student would be given first​?

a. ​Matched-pairs design b. The score on the testscore on the test c. The factor is the type of presentationpresentation. The treatments are by tutorialsby tutorials and giving a lecturegiving a lecture. d. the students e. To eliminate bias as to which presentationpresentation was used first f.

Researchers wanted to evaluate whether a certain herb improved memory in elderly adults as measured by objective tests. To do​ this, they recruited 86 men and 133 women older than 60 years and in good health. Participants were randomly assigned to receive the​ herb, 40 mg 3 times a​ day, or a matching placebo. A measure of memory improvement was determined by a standardized test of learning and memory. After 6 weeks of​ treatment, the data indicated that the herb did not increase performance on standard tests of​ learning, memory,​ attention, and concentration. These data suggest​ that, when taken following the​ manufacturer's instructions, the herb provides no measurable increase in memory or related cognitive function to adults older than 60 years with healthy cognitive function. Complete parts​ (a) through​ (g) below. ​(a) What type of experimental design is​ this? (b) What is the population being​ studied? (c) What is the response variable in this​ study? ​(d) What is the factor that is manipulated and fixed at a single​ level? What are the​ treatments? What is the factor that is manipulated and fixed at a single​ level? What are the​ treatments? ​(e) Identify the experimental units. Choose the correct answer below. (f) What is the control group in this​ study?

a.Completely randomized design b. Adults older than 60 years and in good health c. The score on the standardized test of learning and memory d. the herb / 40 mg 3 times a day or a matching placebo e.The 86 men and 133 women older than 60 who are in good health that participated in the study f. The placebo group serves as the control group because this group corresponds to the reference point that will be compared to the other group.

Treatment

an experiment is a controlled study conducted to determine the effect varying one or more explanatory variables or factors has on a response variable. Any combination of the values of the factors is called a treatment.

Experimental unit

is a person, object or some other well-defined item upon which a treatment is applied. We often refer to the experimental unit as a subject when he or she is a person. The subject is analogous to the individual in a survey.

matched pairs design

is an experimental design in which the experimental units are paired up.The pairs are selected so that they are related in some way (that is, the same person before and after a treatment, twins, husband and wife, same geographical location, and so on). There are only two levels of treatment in a matched-pairs design.

Design an experiment

means to describe the overall plan in conducting the experiment. conducting an experiment requires a series of steps.

Double-blind experiment

neither the experimental unit nor the researcher in contact with the experimental unit knows which treatment the experimental unit is receiving

Blinding

refers to nondisclosure of the treatment an experimental unit is receiving. There are two types of blinding: single blinding and double blinding

a control group

serves as a baseline treatment that can be used to compare it to other treatments. ex: a researcher in education might want to determine if students who do their homework using an online homework system do better on an exam than those who do their homework from the text. The students doing the text homework might serve as the control group (since this is the currently accepted practice). The factor is the type of homework. There are two treatments: online homework and text homework.

Single blinding experiment

the experimental unit (or subject) does not know which treatment he or she is receiving.

determine the factors that affect the response variable

the factors are usually identified by an expert in the field of study. in identifying the factors, ask, "what things affect the value of the response variable?" after the factors are identified, determine which factors to fix at some predetermined level, which to manipulate and which to leave uncontrolled.

response variable

the quantitative or qualitative variable for which the experimenter wishes to determine how its value is affected by the explanatory variable

Confounding

when the effect of two factors (explanatory variables on the response variable) cannot be distinguished, the effect of any one factor cannot be accurately generalized to the population. in this case, a randomized block design should be used.