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Chapter 5 – Producing Data YMS – 5.1

Chapter 5 – Producing Data YMS – 5.1. Designing Samples. Lots of Vocabulary. Observational Study Does not attempt to influence the responses Experiment Deliberately imposes some treatment on individuals in order to observe their responses

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Chapter 5 – Producing Data YMS – 5.1

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  1. Chapter 5 – Producing DataYMS – 5.1 Designing Samples

  2. Lots of Vocabulary • Observational Study • Does not attempt to influence the responses • Experiment • Deliberately imposes some treatment on individuals in order to observe their responses • When goal is to understand cause/effect, experiments are only source of fully convincing data

  3. Statistical Questions from the Classroom

  4. Population • Entire group of individuals we want info about • A census attempts to contact everyone • Sample • Part of the population we actually examine • Sampling is studying a part in order to gain information about the whole • Done because time, cost, and inconvenience forbid contacting every individual

  5. Sampling Frame • List from which a sample is actually selected • Sample Design • Method used to choose sample from population • Poor design can produce misleading conclusions • Bias • Systematically favoring certain outcomes

  6. Types of Samples • Voluntary Response • People who choose themselves by responding (usually have strong negative opinions) • Convenience • Choose the individuals that are easiest to reach • Simple Random (SRS) • Consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

  7. Stratified Random • Divide the population into groups (strata), take an SRS of each group, combine results • Systematic Random • Randomly choose a starting point and select remaining individuals systematically • Multistage Sampling Design • Select successively smaller groups (state, county, city, neighborhood, block) • Probability • A sample chosen by chance • Must know every possible sample

  8. Beware! • Undercoverage • groups in the population are left out of the process of choosing the sample • When sampling frame is smaller than population • Nonresponse • individual chosen can’t be contacted or doesn’t cooperate • Response Bias • Occurs due to behavior of interviewer or respondent • Wording of Questions • Most important influence on the answers given to a sample survey

  9. Random Digits Table • Each entry is equally likely to be any of the digits 0-9 • Entries are independent of each other • Choosing an SRS – Label & Table • Label with the fewest digits possible (i.e. 01 to 99 instead of 001 to 100) • Clearly identify labeling method – very important step for any simulation

  10. Inference About Population • Larger random samples give more accurate results than smaller samples BUT we have to beware of compromising independence. • Sampling with or without replacement 5.1 Practice/Homework: p273 #5.2, 5.5-5.8, 5.10-5.11, 5.13, 5.15, 5.17-5.18, 5.24-5.26, 5.30 5.1 Graded Activity/Classwork: Poker Analysis and Numb3rs “Traffic” episode

  11. YMS – 5.2 Designing Experiments

  12. Vocabulary for Experiments • Experimental Unit • Individuals on which the experiment is being done • Subject • When units are human beings • Factor • Explanatory variables in an experiment • Level • Possible combination of factors • Treatment • Experimental condition applied to the units • Placebo • Dummy treatment

  13. Placebo Effect • Favorable response just because it’s a treatment • Mind over body • Double-Blind • Neither the subject nor the researcher knows which treatment any subject has received • Comparative Experiments • Using a control group to compare several treatments in the same environment • Statistical Significance • An observed effect so large that it would rarely occur by chance • AKA The entire second semester of this class

  14. Principles of Experimental Design • Control • Effects of lurking variables • Randomize • Treatments • Replicate • On many units to reduce chance variation

  15. Block Design • Blocks are groups of experimental units known before the experiment to be similar in some way that is expected to affect the response to the treatments • Random assignment of treatments is carried out separately within a block

  16. p303 • Blocks allow us to draw separate conclusions about each block, i.e. men and women… • A wise experimenter … • Matched Pairs • Blocking design which compares two treatments by choosing blocks of units that are as closely matched as possible • Order of treatment is assigned randomly

  17. 5.2 Practice/Homework p293 #5.31-5.36 P303 #5.44-5.45 P306 #5.50, 5.52, 5.54 5.2 Classwork Read “Healthier and Happier” Article, News clips M*A*S*H clip, Blocking with Dogs AP Practice questions and p308 #5.56

  18. YMS – 5.3 Simulating Experiments

  19. Vocabulary • Simulation • Imitation of chance behavior • Independent Events • The result of one event has no effect or influence on another

  20. Steps of a Simulation • State the problem or describe the experiment. • State the assumptions. • Assign digits to represent outcomes. • Simulate many repetitions. • State your conclusions. 5.3 Practice/Homework: p314 #5.60-5.61, 5.86 Ch 5 Review: p319 #5.74, 5.76, 5.82-5.83

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