Section 1-3 Objectives Identify the five basic sample techniques Data Collection In research, statisticians use data in many different ways. Data can be used to describe situations. Data can be collected in a variety of ways, BUT if the sample data is not collected in an appropriate way, the data may be so completely useless that no amount of statistical torturing can salvage them. 1
Basic Methods of Sampling Random Sampling Selected by using chance or random numbers Each individual subject (human or otherwise) has an equal chance of being selected Examples: Drawing names from a hat Random Numbers Basic Methods of Sampling Systematic Sampling Select a random starting point and then select every k th subject in the population Simple to use so it is used often Basic Methods of Sampling Convenience Sampling Use subjects that are easily accessible Examples: Using family members or students in a classroom Mall shoppers 2
Basic Methods of Sampling Stratified Sampling Divide the population into at least two different groups with common characteristic(s), then draw SOME subjects from each group (group is called strata or stratum) Results in a more representative sample Basic Methods of Sampling Cluster Sampling Divide the population into groups (called clusters), randomly select some of the groups, and then collect data from ALL members of the selected groups Used extensively by government and private research organizations Examples: Exit Polls Stratified vs Cluster Sampling Stratified Cluster 3
Sampling Methods State which sampling method was used. Out of 10 hospitals in a municipality, a researcher selects one and collects records for a 24 hour period on the types of emergencies that were treated there. CLUSTER A researcher divides a group of student according to gender, major field, and low, average, and high GPA. Then, she randomly selects six students from each group to answer questions in a survey. STRATIFIED The subscribers to a magazine are numbered. Then a sample of these people is selected using random numbers. RANDOM Every 10 th bottle of Diet Cola is selected, and the amount of liquid in the bottle is measured. The purpose is to see if the machines that fill the bottles are working properly. SYSTEMATIC Bellwork with Group.. Applying the Concepts Sections 1.3 Page 1-17 & page 1-17 #11 16 all 4
Section 1-4 Objectives Explain the difference between an observational and an experimental study Types of Studies Observational Studies The researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations No interaction with subjects No modifications on subjects Occur in natural settings Can be expensive and time consuming Example: Counting cars as they drive by. 5
Surveys Telephone Mailed Questionnaire Personal Interviews Less costly than personal interviews Subjects are more candid than if face to face Challenge---some subjects do not have phone, will not answer when called, or hang up (refusal to participate) Tone of voice of interviewer may influence subjects responses Cover a wider geographic area than telephone Less expensive than telephone Subjects remain anonymous Challenge low number of subjects respond, inappropriate answers to questions, subjects have difficulty reading/understanding the questions Provides in-depth responses Interviewers must be trained Most costly of three Interviewer may be biased in his/her selection of subjects Types of Studies Experimental Studies The researcher manipulates one of the variables and tries to determine how the manipulation influences other variables Interaction with subject occurs Modifications on subject occurs May occur in unnatural settings (labs or classrooms) Example: Clinical trials of new medications,treatments, etc. Partner chat! For each of the following scenarios determine whether a sample survey, observational study, or experiment would be best. EXPLAIN YOUR ANSWER. We will discuss as a group in a few minutes. 1. What percentage of teenagers leave the water running when they brush their teeth? 2. Which of two drugs is more effective at preventing nausea following the onset of a migraine? 3. Do male or female teenagers tend to have more numbers stored in their cell phones? 4. What percent of drivers come to a complete stop at a stop sign near a local elementary school? 5. Does printing suggested tip amounts on the bottom of a restaurant bill increase the average amount that customers leave in tips? 6
Independent/Dependent Variable Independent variable Manipulated/Controlled by researcher Explanatory variable Dependent Variable Resultant variable Outcome variable Independent/Dependent Variable The grade on a test depends on the number of questions answered correctly The number of calories consumed in a week determines the number of pounds lost(or gained) that week. A burning candle is an example of a functional relationship. The variables are the height of the candle and the amount of time the candle has been burning. Heart rate is a function of the amount of activity someone is engaged in. The variables are heart rate and activity level. 7
Independent/Dependent Variable The grade on a test depends on the number of questions answered correctly The number of calories consumed in a week determines the weight that week. A burning candle is an example of a functional relationship. The variables are the height of the candle and the amount of time the candle has been burning. Heart rate is a function of the amount of activity someone is engaged in. The variables are heart rate and activity level. Sources of Misuse There are two main sources of misuse of statistics: Evil intent on part of a dishonest researcher Unintentional errors (stupidity) on part of a researcher who does not know any better Misuses of Statistics Samples Voluntary-response sample (or self-selected sample) One in which the subjects themselves decide whether to be included---creates built-in bias Telephone call-in polls (radio) Mail-in polls Internet polls Small Samples Too few subjects used Convenience Not representative since subjects can be easily accessed 8
Misuses of Statistics Graphs Can be drawn inappropriately leading to false conclusions Watch the scales Omission of labels or units on the axes Exaggeration of onedimensional increase by using a two-dimensional graph Is there anything wrong? Misuses of Statistics Survey Questions Loaded Questions---unintentional wording to elicit a desired response Order of Questions Nonresponse (Refusal) subject refuses to answer questions Self-Interest ---Sponsor of the survey could enjoy monetary gains from the results 9
Misuses of Statistics Missing Data (Partial Pictures) Detached Statistics ---no comparison is made Percentages -- Precise Numbers People believe this implies accuracy Implied Connections Correlation and Causality when we find a statistical association between two variables, we cannot conclude that one of the variables is the cause of (or directly affects) the other variable The Hawthorne Studies Studies of how characteristics of the work setting affected worker fatigue and performance at the Hawthorne Works of the Western Electric Company from 1924-1932. 2-29 The Hawthorne Studies Worker productivity was measured at various levels of light illumination. Researchers found that regardless of whether the light levels were raised or lowered, worker productivity increased. 2-30 10
With a partner Bias Activity Worksheet Homework Page 1-25 #27 46 all Due Friday at the start of class 11