DATA: numbers with a contextThe number “75” carries no information, but a “75 lb dog” engages our background knowledge and allows us to make judgements.STATISTICS: the process of collecting, organizing, and drawing conclusions from data.1) Data beat anecdotes— a striking story that sticks in our mindsNational Cancer Institute spent 5 years and $5 million and determined there is no connectionbetween leukemia and exposure to magnetic fields produced by power linesVS.1 television interview with a mother whose child has leukemia and happens to live near a power line.2) Check the origin of the dataAnn Landers asked her readers whether they would have children again, 70% of almost 10,000 responses said noOpinion polls have shown most parents don’t regret having children 3) Beware of hidden variables—“what other information could explain this” Lurking variables/confoundingCrime is higher in counties with gambling casinosCrime is higher in urban & poor counties (where casinos are typically built)Loras gives students with better grades 1st choice at housing—is this fair?4) Variation is everywhereRepeated measurements (height/weight/temperature) on the same person will vary5) Statistical conclusions are not absoluteSmoking causes lung cancer6) Data reflect social values—Society influences what and how we measureCatholic countries typically have fewer suicides than Japan“Unemployment” rate only considers people who want a job AND have actively looked in the last 2 weeks (4 weeks)Chapter 3 Getting Trustworthy DataDoes your sample data represent an entire population?POPULATION: the entire group of individuals about which we want informationSAMPLE: a part of the population from which we actually collect informationused to draw conclusions about the whole11) OBSERVATIONAL STUDY : Observes individuals and measures variables of interest in order to describe some group or situation. Does not attempt to influence the responsesJane Goodall watched chimps to realize that they were not vegetariansSample Survey - a sample is selected and observed because it is believed they represent the entire populationExample: Poll asks voters who they will elect. If the pollsters only call homes between 9-5, then the population isn’t really the entire US population, but only people in the US that are at home during 9-5. NOTE if 50 or 50,000 people were called in this sample it still doesn’t change the fact that it does not represent the US population.Example: Nielsen ratings do not call college campuses (how does this affect advertising sales for WB)CENSUS: A sample survey that attempts to include the entire population in the sample--time consuming and expensive (can’t do census with destructive testing)--a careful sample can produce more accurate data then a census2) EXPERIMENT : A treatment is imposed on an individual before results are measured in order to determine whether the treatment caused a change in the result.Experiments can give evidence for cause and effect relationships (on average, but not every individual)3.2 Design of ExperimentsRESPONSE VARIABLE: measures an outcome/result of a study (dependent)EXPLANATORY VARIABLE: might explain or causes changes in the response variable (independent)Often called factors May be several levels of each factorSUBJECT: Individual, Experimental UnitTREATMENT: experimental condition applied to subjectsEach trt may be specific levels of several factorsCollege students at Nova Southeastern University have the option of taking the course on line.Abecedarian Project 111 (healthy, low-income black infants in 1972). All infants received nutritional supplements and help from social workers. ½ chosen at random were placed in an intensive preschool program. Over time measured test scores, college attendance, and employment of these childrenPlacebo: a dummy treatmentExample 3.5 p 231 Gastric Freezing to prevent ulcers 2Randomization uses chance to assign subjects to the trt. -- Creates trt groups that are similar before the trt is applied-- Prevents biasBIASED: A statistical study that systematically favors certain outcomes-- typically due to hidden (lurking) variablesSIMPLE RANDOM SAMPLE ( SRS ): of size n 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.--each individual in the population has an equal chance of being selectedJoans accounting firm serves 30 clients, and wants to interview a sample of 5 clients to improve client satisfaction.Step 1) Label each client01 A-1 Plumbing 16 JL Records02 Accent Printing 17 Johnson Commodities03 Action Sport Shop 18 Keiser Construction04 Anderson Construction 19 Liu's Chinese Restaurant05 Bailey Trucking 20 MagicTan06 Balloons, Inc 21 Peerless Machine07 Bennett Hardware 22 Photo Arts08 Best's Camera Shop 23 River City Books09 Blue Print Specialties 24 Riverside Tavern10 Central Tree Service 25 Rustic Boutique11 Classic Flowers 26 Satellite Services12 Computer Answers 27 Scotch Wash13 Darlene's Dolls 28 Sewer's Center14 Fleisch Realty 29 Tire Specialties15 Hernandez Electronics 30 Von's Video StoreStep 2) Enter Table B anywhere and read two-digit groups line 130 shows: 69051 64817 87174 09517 84534 06489 87201 97245two-digit groups are: 69 05 16 48 17 87 17 40 95 17 84 53 40 64 89 87 20 19 72 05 16 17 20 19 are the 5 clients selectedRandomized Comparative Experiment - randomization produces similar groups- comparative design eliminates confounding other influences (lurking variables) operate equally on all groups- use enough subjects to reduce chance variation in results then we conclude differences in the response variable are due to the effect of the treatmentsControl of the effects of lurking variables on the response, 3Randomization the use of impersonal chance to assign experimental units to trtsReplication of the experiment on many units reduce chance variation in the resultsCOMPLETELY RANDOMIZED experimental design: all subjects are allocated at random among all the treatments.Effects of TV advertising (length, repetition)1 time 3 times 5 times30 sec Trt 1 Trt 2 Trt 390 sec Trt 4 Trt 5 Trt 62 explanatory, 6 Trts (interactions may be negative)MATCHED PAIRS DESIGN: compares 2 trts by pairs of subjects that are closely matched as possibleRight & left hand Pepsi VS. CokeBLOCK DESIGN: the subjects are randomly assigned within