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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.

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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 kth

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

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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 SamplingStratified Cluster

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Sampling MethodsState 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.

• 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.

• The subscribers to a magazine are numbered. Then a sample of these people is selected using random numbers.

• Every 10th 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.

CLUSTER

STRATIFIED

RANDOM

SYSTEMATIC

Bellwork with Group..Applying the Concepts

Sections 1.3

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page 1-17

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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.

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SurveysTelephone Mailed Questionnaire Personal Interviews

Less costly than personal interviews

Cover a wider geographicarea than telephone

Provides in-depth responses

Subjects are more candid than if face to face

Less expensive than telephone

Interviewers must betrained

Challenge---some subjects do not have phone, will not answer when called, or hang up (refusal to participate)

Subjects remainanonymous

Most costly of three

Tone of voice of interviewer may influence subjects’ responses

Challenge –low number of subjects’ respond, inappropriate answers to questions, subjects have difficulty reading/understanding the questions

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?

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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.

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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

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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 one-dimensional 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

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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

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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.

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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.

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With a partner

Bias Activity Worksheet

HomeworkPage 1-25

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Due Friday at the start of class