Name:____________________________________________________ AP Statistics Date: Experimental Design Review Answer True if the statement is always true. If not, change the bold-faced, underlined word(s) so that the statement is always true. _Double-Blind__ 1) A single-blind experiment is an experiment in which the experiment units and the evaluator of the experiment do not know which treatment the units received. Only one group is blinded in single _______True__ 2) The basic principles of expe
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  Name:____________________________________________________ Date: AP Statistics Experimental Design Review Answer True  if the statement is always true. If not, change the bold-faced, underlined  word(s) so that the statement is always true.  _Double-Blind__  1) A single-blind  experiment is an experiment in which the experiment units and the evaluator of the experiment do not know which treatment the units received.   Only one group is blinded in single  _______True__  2) The basic principles of experimental design are control, replication, randomization, and blocking .  ___Randomization 3) Blocking  reduces bias. ***Blocking reduces variation  _______True__  4) A block  is a group of experimental units that are similar in ways that are expected to affect the response to treatments.  ____Replication___  5) Control  of the   treatments on many units reduces the role of chance variation.  ______True_______  6) The design of an experiment  refers to the choice of treatments and the manner in which the experimental units are assigned to the treatments. Completely Randomized 7) In a randomized block  experiment, all the experimental units are allocated at random among all the treatments.  __Experiment______  8) Causation can only be shown with a well-designed, well-controlled observational study .  ___Larger________  9) Smaller  samples produce statistics that have less variability.   In general larger samples tend to have less variability because the chance of variation is spread out more.  _Reduces_________  10) Random assignment of experimental units to treatment groups eliminates  bias in the response variable. Random assignment will not completely remove bias, but it will help to reduce the effects of bias by spreading it out evenly amongst the subjects.  ___True__________  11) A placebo  is a treatment that contains no active ingredients.  __True___________  12) Two factors are confounded  if their effects on the response variable cannot be distinguished from one another. Fill in the blank with the word(s) that make it a true statement. 13) Blocks are homogenous groups with similar characteristics. 14) Blocking is used in an experiment to filter out the effects of a(n) confounding variable _. 15) A(n) observational study is a study in which participants are followed into the future and events are recorded. 16) The control  group is treated identically in all respects except that they don’t receive the active treatment.  17) In a matched pairs design, individual subjects can be used as their own control by give randomizing the order of the treatment to the subject. 18) In a blocked randomized design, experimental units are divided into groups by some criteria that might be confounding before being randomly assigned to treatments. 19) The response variable is the variable that is being tested.  Multiple Choice   20)   In an observational study, confounding means a)   having more than one response variable. b)   That the effect of the explanatory variable on the response variable changes for different categories of a third variable. c)   That the effects of several variables are tested at one time. d)   That the effect of the explanatory variable on the response variable can’t be separated from the effect of other variables on the response variable. e)   None of the above. 21)   Control g roups are used in experiments in order to …  a)   control the effects of confounding variables such as the placebo effect.. b)   control the subjects of a study so as to insure all participate equally. c)   guarantee that someone other than the investigators, who have a vested interest in the outcome, control how the experiment is conducted. d)   achieve a proper and uniform level of randomization. e)   obtain consistency in the experiment. 22)   A nutritionist wants to study the effect of storage time (6, 12, and 18 months) on the amount of vitamin C present in freeze dried fruit when stored for these lengths of time. Vitamin C is measured in milligrams per 100 milligrams of fruit. Six fruit packs were randomly assigned to each of the three storage times. The treatment (Trt), experimental unit (EU), and response variable (RespVar) are respectively: a)   Trt: a specific storage time; EU: amount of vitamin C; RespVar: a fruit pack b)   Trt: a fruit pack; EU: amount of vitamin C; RespVar: a specific storage time c)   Trt: random assignment; EU: a fruit pack; RespVar: amount of vitamin C d)   Trt: a specific storage time; EU: a fruit pack; RespVar: amount of vitamin C e)   Trt: a specific storage time; EU: the nutritionist; RespVar: amount of vitamin C 23)   A group of 420 college students are enrolled in a blind taste test. The school’s food service wants to see if they can improve the taste of their lattes. They decide to try two types of coffee beans (Arabica and Robusta); three types of syrup (vanilla, hazelnut, and mocha); and two types of milk (soy and low fat). The best combination of ingredients is sought. The latte experiment will have a) 2 factors, 7 levels, and 420 treatments b) 2 factors, 3 levels, and 12 treatments c) 3 factors, 7 levels, and 420 treatments d) 3 factors, 12 levels, and 420 treatments e) 3 factors, 7 levels, and 12 treatment For questions 24-26: Researchers would like to compare meditation and exercise to see which is more effective for reducing stress. One hundred people who suffer from high stress volunteer to participate in a study for ten weeks. Participants will either be given a 10-week course in meditation or will participate in a 10-week exercise program. The researchers must decide whether to randomly assign the volunteers to the two programs or allow the volunteers to choose. 24)   Which of the following is the main advantage of randomly assigning participants to the two programs rather than allowing them to choose? a)   The participants are more likely to stick with the program for the full 10 weeks. b)   Confounding variables, such as past practice with meditation, should be approximately equal for the two groups. c)   Random assignment ensures that the two sample sizes are equal and that requirement is necessary in studies like this one. d)   Random assignment will allow the results to be extended to the population of all adults.  e)   None of the answers above are correct. (Because are dealing with volunteers randomizing is necessary to reduce bias.) 25)   Suppose participants are randomly assigned to the two programs and a psychologist measures their stress levels before and after the 10-week program, without being told who is which program. This experiment would be: a)   Single-blind as long as the participants are not told the results of the stress level measurements. b)   Single- blind because the psychologist doesn’t know who is in which program, but the participants do know. c)   Double-blind as long as the participants are not told the results of the stress level measurements. d)   Neither single nor double blind. e)   Not an experiment. 26)   In this study, the stress level measurement after the 10-week program is an example of a)   A randomly assigned treatment. b)   An explanatory variable. c)   A response variable. d)   A normal variable. e)   A confounding variable. 27)   For one kindergarten class in DPISD, a researcher determines which children already can read simple words and which children cannot upon entering kindergarten. The children are followed until third grade, at which point they are tested to determine the grade level at which they are reading. Those children who were reading simple words on entering kindergarten are found to be reading at a higher level on average than those who could not read simple words on entering kindergarten. The researcher a)   can conclude that children should be taught to read in preschool, as there are clear benefits to reading early. b)   cannot conclude that being able to read before entering kindergarten is beneficial, as there may be confounding variables in this study. c)   needs to have taken a random sample of kindergarten students instead of one class to conclude a cause-and-effect relationship. d)   needs to retest in sixth grade or no conclusion can be reached. e)   needs to enroll in AP Statistics at DPHS to be better equipped to answer this question.  Free-Response 28) An equipment firm is trying out three new types of grease in the transmissions of its front-end loaders. The maintenance manager is interested in whether any of the greases reduce the time before the transmissions have to be repaired. The company has 30 brand new front-end loaders (all are the same type) to use in the test. How would you design the experiment and how would you assign the front-end loaders? Be specific! Would you use a completely randomized design or a randomized block design? How many factors are there? How many treatments? If it is randomized block, what characteristic identifies the blocks? Explain you decisions. A completely randomized design will be used for this experiment. We will assign the 30 front-end loaders using a random number generator. 1-10 will receive treatment 1, 11-20 receive treatment 2. 21-30 will receive treatment 3. We will compare the time until transmissions must be repaired between all three groups. There is only 1 factor (the grease used), 3 treatments, and the response is the amount of time until the transmissions must be repaired. 29) Suppose you are interested in determining whether a daily dose of vitamin C helps prevent colds. You recruit 20 volunteers to participate in an experiment. You want half of them to take vitamin C and the other half to agree not to take it. You ask each subject which they prefer, and ten say that they would like to take the vitamin C and the other ten say they would not. You ask each of them to record how many colds he or she gets during the next ten weeks. At the end of the time, you compare the results reported from the two groups. Give two reasons why this is not a good experiment. Give one example of a variable that could confound the results of this experiment. It cannot be a restatement of one of the two reasons given to the previous question. There is no randomization of the treatment being imposed to participants. Because of this error, bias may have been introduced in the way the subjects are allowed to pick their own groups. Some people may be healthier and take Vitamin C supplements on a regular basis while others may not. You are also asking the participants to distinguish what they may perceive as being a cold. A cold may be sneezing sniffling to some, while it may be a fever to others. Possible confounding issues may be lifestyle, prior health, and diet. 30) A new type of fish food has become available for salmon raised on fish farms. Your task is to design an experiment to compare the weight gain of salmon raised over a six-month period on the new and the old types of food. The salmon you will use for this experiment have already been randomly placed in eight large tanks in a room that has a considerable temperature gradient. Specifically, tanks on the north side of the room tend to be much colder than those on the south side. The arrangement of tanks is shown on the right. Design an experiment that takes into account this temperature gradient. 30 Front End Loaders 10 Front End Loaders 10 Front End Loaders 10 Front End Loaders Treatment 1 Treatment 2 Treatment 3 Compare the times until transmissions must be repaired.      R  a  n   d  o  m   i  z  e 8 Fish tanks North Window North Door South Heater South No Heater Tanks 1, 4 Tanks 2,3 Tanks 6, 7 Tanks 5, 8 Treatment New Food Treatment Control Treatment New Food Treatment Control Treatment New Food Treatment Control Treatment New Food Treatment Control Compare the weight gain in each block or matched pair. We will block by location of the tanks. We will then form a matched pairs based on the location. We will randomize which tank gets the treatment and control in each pair by flipping a coin (H-treatment/T-control). We will then compare the weight gamin of each fish in each pair. Block by LocationMatchby factors present in roomRandomize

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