Where Do Data Come From? The field of statistics is applicable in every discipline. To give an idea of how widespread its use is, consider the following examples illustrating the scope of applications: From ratemyprofessors.com, STAT 110 instructors often get comments about the practice test looking like the real exam…..should you believe this claim? Here are some interesting stats from Exam 2 last semester Summary statistics: • • A claim found on MedPageToday http://www.medpagetoday.com/Pediatrics/GeneralPediatrics/36848?utm_content=&utm_medium=email&utm_campaign=DailyHeadlines&utm_source=WC&xid=NL_DHE_2013-01-15&eun=g387768d0r&userid=387768&[email protected]&mu_id=5380723 “Fast Foods Tied to Allergies, Excema in Kids” Can we believe this claim? Let’s look at the article…. Another claim found on MedPageToday http://www.medpagetoday.com/MeetingCoverage/AAIC/33780?utm_source=breaking-news&utm_medium=email&utm_campaign=breaking-news “IVIG Stops Alzheimer’s in Its Tracks” 51% of adults age 18 and older are married today – 72% in 1960 http://www.pewsocialtrends.org/2011/12/14/barely-half-of-u-s-adults-are-married-a-record-low/?src=sdt-carousel Column n Mean Variance Std. Dev. Std. Err. Median Range Min Max Q1 Q3 Exam 2 379 78.51715 318.37735 17.843132 0.9165401 82 102 0 102 70 90Chapter 1 Page 2 Statistics is the science (or art) of data. _____________________are the objects described by a set of data. Individuals may be people, but they may also be animals or things. A _____________________is any characteristic of an individual. A variable can take different values for different individuals. The actual measurements recorded for individuals are called ___________. Example 1 What are the individuals? What are the variables? Example 2 Individuals? Variables? Name Major Points Grade Advani, Sura Comm 397 B Barton, David Hist 323 C Brown, Annette Lit 446 A Chiu, Sun Psyc 405 B Cortez, Maria Psyc 461 A Make Vehicle Transmission Cylinders City Highway BMW Subcompact Automatic 6 19 27 BMW Subcompact Manual 6 20 29 Buick Midsize Automatic 6 20 30 Chevy SUV (2WD) Automatic 6 16 21Chapter 1 Page 3 Example 3 In an agricultural study in Kansas, researchers want to know which of three fertilizer compounds produces the highest wheat yield (in kg/plot). An experimenter uses 15 plots of land. Each fertilizer is applied to 5 plots of land. After harvest, the resulting yield is measured. Individuals? Variables? Ways to Gather Data 1. Observational Study An observational study observes individuals and measures variables of interest but does not attempt to influence the responses. A response variable is a variable that measures an outcome or result of a study. The purpose of an observational study is to describe some group or situation. The ____________________ for a statistical study is the entire group of individuals about which we want information. A ____________________ is the part of the population from which we actually collect information and is used to draw conclusions about the whole. 2. Sample Survey A Sample survey is a type of observational study that surveys a group of individuals by studying only some of its members (selected because they represent the larger group of individuals) It is a survey because the individuals provide their own responses It is a sample survey because the individuals participating in the survey are a sample of the population Fertilizer 1 Fertilizer 2 Fertilizer 3 64.8 56.5 65.8 60.5 53.8 73.2 63.4 59.4 59.5 48.2 61.1 66.3 55.5 58.8 70.2Chapter 1 Page 4 A census is a sample survey that attempts to include the entire population as the sample. The US Census is required by the constitution every 10 years You can see 2010 Census Data and info here http://www.census.gov/2010census/ Lots of really cool data can be found here. Let’s take a look at some in class. We’ll always miss some people in the census count… http://www.cnsnews.com/news/article/dozens-us-cities-line-contest-2010-censu Example 4 The University of Pennsylvania’s National Annenberg Election Survey conducted a poll from July 30 to August 5, 2004. They asked: Do you favor or oppose Federal funding of research on diseases like Alzheimer’s using stem cells taken from human embryos? The survey reported that the poll consisted of 1345 randomly selected adults in the United States. Population? Sample? Example 5 The American Community Survey (ACS) contacts 3 million households, including some in every county in the US. This new Census Bureau survey asks each household questions about their housing, economic, and social status. Population? Sample? Example 6 Video adapter cables have pins that plug into slots in a computer monitor. The cable will not work if pins are bent or broken. A store chooses 5 cables from each lot and inspects the pins. If any of the cables have bent or broken pins, the entire lot is sent back. Population? Sample?Chapter 1 Page 5 Example 7 A sociologist wants to know the opinions of employed adult women about government funding for day care. She obtains a list of the 580 members of a women’s club and mails a questionnaire to 100 of these women selected at random. Only 41 questionnaires are returned. Population? Sample? What percentage of the women contacted responded? 3. Experiment An experiment deliberately imposes some treatment on individuals in order to observe their responses. The purpose of an experiment is to study whether the treatment causes a change in the response. Virtually all scientific research involves conducting well-designed experiments. Researchers hope the results from these experiments support a research hypothesis. Example 8 Salmonella bacteria are widespread in human and animal populations, and there are over 2,000 known serotypes. The reported incidence of salmonella illnesses in humans is about 17 cases per 100,000 people. A food scientist wants to see how withholding feed from pigs prior to slaughter can reduce the size of gastrointestinal tract lacerations during the actual slaughtering process. This is an important issue since pigs infected with salmonella may contaminate the food supply through these lacerations (among other routes, including fecal matter and meat juices). He chose 45 pigs from 3 farms. Individuals = Population = Sample =Chapter 1 Page 6 Three treatments (we’ll give a formal definition of “treatment” in