Presentation on theme: "Statistics The science of collecting, analyzing, and interpreting data. Planning A Study Using The Statistical Problem Solving Process: Ask a question."— Presentation transcript:
1 StatisticsThe science of collecting, analyzing, and interpreting data.Planning A Study Using The Statistical Problem Solving Process:Ask a question of interestCollect some dataAnalyze and describe the dataMake a conclusion, answering the question of interest
2 2 Types of Studies Observational Study Experimental Study -Record data observed or surveyed-No treatments imposed-Used to describe a group or situation-Impose treatments on subjects-Record results and compare groups-Used to see if the treatments cause a change in the responseExperimental Study
3 Measuring Data from Study Subjects or Experimental Units Various VariablesExplanatory (independent, x) variable: the treatment in an experiment or group label in an observation (may not exist in observational studies)Response (dependent, y) variable: the result measured in the end of every experimental and observational studyConfounding variable: a variable that might exist in a study that influences the response but can’t be separated from the explanatory variable
4 Example of confounding A study sites that a group of children who had certain vaccinations were more likely to develop autism than a group of children who did not receive those same vaccinations. Does this mean that vaccinations cause autism?Explanatory:Response:Possible confounding:Effect of confounding:Whether or not they were vaccinatedWhether or not they developed autismVaccination group could have also given children some new diet or supplement that non-vaccination group didn’t giveVaccination group’s higher rate of autism may be tied to diet or supplement rather than vaccination
5 CensusThe systematical collection of data on every single subject in the population.When the population is large, it will be time consuming and expensive.Video on census/American Community Survey use at Target:Difference between ACS and Current Population Survey:
6 Observational Studies Subjects are randomly selected and asked questions or observed in a particular setting.Subjects are not influenced in how they respond.
7 Good Survey Questions Avoid unnecessary complexity to question Avoid misleading questionsRandomize ordering of questionsEnsure confidentialityAvoid influencing the subject by tone, appearance, or suggestionVideo 17, start at 4:46, 2.5 min
8 Sources of bias in surveys If a selection process consistently obtains values too high or too low, then bias exists. Some group may be under (or over) represented.Response Bias: influencing the response in some way-Non-response bias: a group is left out because they feel uncomfortable, too busy, etc.Selection Bias : not randomly selected from the entire population of interest
9 Sampling VocabularyPopulation of Interest the set of people or things you wish to know something aboutSampling frame a list of all subjects from which the sample is takenWhat is the difference between the sampling frame and the population of interest?Sample a portion of the population that is selected to represent the population of interestRandom sampling a way of getting a sample that reduces selection biasHow could we ensure a sample is randomly selected?When is the sampling frame not the same as the population of interest?
11 Sampling Methods Simple Random Sample (SRS) Stratified Random Sampling Cluster SamplingSystematic SamplingMulti-Stage SamplingRandom Digit DialingSelf-Selected SampleConvenience SampleJudgment Sample“Quickie Polls”SRS and Stratified sampling methods are tested on the AP exam.
12 Simple Random Sampling From the entire populationevery unit has the same chance of belonging to the sampleand every possible grouping of specified size has same chance of being selected.Like drawing names out of a hat
13 Stratified Sample vs. Cluster Sample some from all all from some 1st divide population into groups (strata), then take a Simple Random Sample from each strata(one or more slips from each hat)1st divide population into groups (cluster), then randomly select some clusters and sample everyone in that cluster(all slips from one or two hats)
14 Systematic Sampling Random Digit Dialing From a list, randomly choose starting point (4th entry), and divide into consecutive segments (every 10 names), then sample at that same point in each segment (4, 14, 24, 34,…)Sample that approximates a SRS of all households that have telephones with a specific exchange( )Pew Research:
15 Samples typically resulting in biased results Self-Selected Sample--radio station call-in Convenience Sample--surveying folks in a mall who appear willing to talk to you Judgment Sample – surveying those you pick as an “expert” selector “Quickie Polls”--hastily designed, poorly pre-tested, one night survey sample for evening news show
16 Random Number TableAssign a number label to each unit in the populationRead numbers from table from left to right, starting anywhere. The subjects selected for the sample are those read from the table.Repeats or those not a part of the list are ignored.
17 Sampling & Lays potato chips Video 16, start at 6:35, about 2 minutesNielsen tv ratings