1-3 Data Collection and Sampling techniques  Data Collection  Surveys:  Most common method  Telephone Survey  Mailed questionnaire  Personal interview  Surveying records  Direct observation

Random sampling  All members of the population have a equal chance of being selected.  Subjects are selected using random numbers  Each subject in the population is numbered  Random numbers are generated using a calculator, computer, or table of random numbers.  The subjects whose numbers are selected are part of the sample  4 basic methods of sampling used to obtain unbiased samples.  Unbiased samples = each subject in the population had an equally likely chance of being selected.

Systematic sampling  Each subject in the population is numbered  Every kth is selected from the population (3 rd, 5 th, 10 th, etc…)  k is a counting number  The first number is selected at random  Numbering is NOT always necessary.

Stratified Sampling  Population is divided into subgroups, strata, according to some characteristic relevant to the study.  A random sample is selected from each subgroup.

Cluster sampling  The population is divided into sections or clusters.  One or more clusters are selected and all members of the cluster(s) are including in the sample.  Clusters are a pre-existing, intact group.

 Other Sampling Methods  Convenience Sample: Uses subjects that are convenient.  Customers entering a mall – favorite store  Customers entering a restaurant – favorite menu item  Students entering a school – favorite subject.  Volunteer sample or self-selected sample.  Respondents decide if they want to be included in the sample  Sampling Error: the difference between the results obtained from a sample and the results obtained from the population from which the sample was selected.  Nonsampling Error: when the data are obtained erroneously or the sample is biased.

1-4 Experimental Design Observational Studies  Researcher observes and draws conclusions based on what is happening or what happened in the past.  3 main types:  Cross-sectional study: the data are all collected at one time.  Retrospective study: data are collected using records obtained from the past.  Longitudinal study: data are collected over a period of time.  Advantages:  Typically occurs in a natural setting  Done in situations where conducting an experiment would be dangerous or unethical.  Studying rapes, suicides, murders, long-term psychological effects of the death of a close relative, effects on children of exposure to lead etc…  Done using variables that cannot be manipulated  Right-handed vs. left-handed, drug user vs. nondrug users  Disadvantages:  Cause-and-effect cannot be shown  Expensive  Time-consuming  Measurements used may have inaccuracies

Experimental Studies  Researcher manipulates one of the variables and tries to determine how the manipulation influences the other variable(s).  Subjects should be assigned to groups randomly  Treatments should be assigned to groups randomly  Quasi-experimental Study: intact groups are used instead of random groups  Advantages:  Researcher decides how to select subjects and assign them to groups  Researcher controls independent variable  Disadvantages:  Unnatural settings—results may not occur in a natural setting  Hawthorne effect: subjects changed their behavior that affected the results of the study

 Independent (explanatory) variable:  variable that is manipulated by the researcher  Type of instruction  Dependent (outcome) variable:  Resultant variable  studied to see if it has changed significantly due to the manipulation of the independent variable.  Confounding Variables: Influences the dependent variable, but cannot be separated from the independent variable.  Subjects taking a pill to help lower cholesterol or subjects in a diet/exercise program may also change their diet or take supplements without the researcher knowing.

Uses and Misuses of statistics  Uses:  Describe data  Compare multiple data sets  Determine if two variables are related  Test hypotheses  Make estimates/predictions about population characteristics

Misuses  Suspect Samples:  Was the sample size small compared to the population?  How were the subjects selected?  Convenience sample  Volunteers  When were the subjects selected and how long did they need them?  Ambiguous Averages  Researchers select the measure of average (Mean, Median, Mode or Midrange) that best supports their position.

 Changing the subject  Different representations of the same value  Uses different units, % vs. $  Why was that unit chosen?  Which unit best represents the data?  Detached Statistics  40% less fat…less fat than WHAT?  1/3 fewer calories…than what?  A comparison is made but you don’t know to what.  Implied Connections  May, can, could, some  Words that don’t commit the author to back it up.

 Misleading Graphs  No scale, or partial scale on axes.  Circles, 3D objects, figures often blur the actual numbers

 Faulty Survey Questions  Leading questions that cannot be answered with yes or no or that produce bias by author.  Don’t you agree that teachers should earn more money than they currently earn?  Yes, they should earn more  No, they should not earn more  Don’t know/no opinion  The phrase “Don’t you agree” leads the respondent. A more neutral wording would be:  Do you believe teacher salaries are a little lower than they should be, a little higher than they should be, or about right?  Teacher salaries are a little lower than they should be  Teacher salaries are a little higher than they should be  Teacher salaries are about right  Don’t know/no opinion

1-3 and 1-4 Progress Check 1. Identify the sampling method used. a) To determine how long people exercise, a researcher interviews 5 people selected from a yoga class, 5 people selected from a weight lifting class, 5 people selected from an aerobics class, and from people from swimming classes. b) In a medical research study, a researcher selects a hospital and interviews all the patients that day. 2. Determine whether an observational or experimental study was used: In a large city, a researcher decides to check the police department records for 2 months to determine what types of vehicles were stolen. 3. Identify the independent and dependent variables: A researcher found that the number of times people visited fast-food restaurants increased with increasing income. (Source: healthland.time.com) 4. York University in Toronto, Canada, stated that people who had suffered from fibromyalgia were able to reduced their pain by participating in twice-weekly yoga sessions. Suggest some confounding variables the researcher might want to consider.

1-3 and 1-4 Progress Check (Answer Key) 1. Identify the sampling method used. a) To determine how long people exercise, a researcher interviews 5 people selected from a yoga class, 5 people selected from a weight lifting class, 5 people selected from an aerobics class, and from people from swimming classes. b) In a medical research study, a researcher selects a hospital and interviews all the patients that day. 2. Determine whether an observational or experimental study was used: In a large city, a researcher decides to check the police department records for 2 months to determine what types of vehicles were stolen. 3. Identify the independent and dependent variables: A researcher found that the number of times people visited fast-food restaurants increased with increasing income. (Source: healthland.time.com) 4. York University in Toronto, Canada, stated that people who had suffered from fibromyalgia were able to reduced their pain by participating in twice-weekly yoga sessions. Suggest some confounding variables the researcher might want to consider.

1-3 and 1-4 Practice Assignments  Pg. 17 #1-4, 5-15odd  Pgs #1-14, 15-41odd