Chapter 5 Section 1.pptx

Chapter 5 Section 1

Producing Data

Collecting and using sample data wisely

 _{Descriptive Statistics, use of numerical and graphical} summaries to characterize a dataset.

 _{Inferential Statistics, use of sample data to make}

conclusions about a broader range of individuals than just those who are observed

 _{Statistical Inference, producing answers to a specific question with a}

know degree of confidence on correctness.

 _{Fundamental Rule For Using Data For Inference, the}

available data can be used to make inferences about a much larger group…if the data can be considered to be

Chapter 5 Section 1

Observational Study & Experiments & Simulations

 _{Observational Study, the researcher simply observes}

individuals and measures variables of interest BUT does not attempt to influence the responses

 _{Example…opinions, behaviors or outcomes ( sources of data about}

topics)

Observational Studies are a poor way to gauge the effect of an intervention. In order to see a response change, the researchers must impose change. When this goal becomes to understand a cause- and –

effect relationship (the change), a researcher should use an experiment.

 _{Observational studies of the effect of one variable on another often}

Chapter 5 Section 1

Observational Study & Experiments & Simulations

 Experiment, the researchers manipulate a something and measure the effect of the manipulation on some outcome of interest

 Randomized experiments…are were participatians are randomly assigned to engage in one treatment or another.

 Designed to pin down the effects of a specific variable of interest  Preferred method of science, medicine and industry

 Simulations, alternative method of producing data

Used only when…

I. It is not possible to observe individuals directly or to perform an experiement

Who do we study?

Who Do Researchers Study

 _{Population, Entire group of individuals that the researcher} wants information about

 _{All NC High School students enrolled in AP Statistics}

 _{A census occurs when we attempt to contact the entire} population

 _{Example: if we want to know the average GPA of AP Stats}

students we would have to collect that data for every HS student currently enrolled in the class

Who Do Researchers Study

 _Sample,

PART

 _{Select specific NC High School students enrolled in AP Stats}

 _{In most cases it is impossible or improbable to study the} population which is why we generally look at only a small sample size

 _{When study only a part of a population this is called}

Sampling.

 _{The GOAL of choosing a sample is a picture of the}

population, disturbed as little as possible by the act of gathering information

Population

Sample

Collect data from a

representative Sample...

Sampling

Note: When making conclusions from sampling a sound design for selecting the sample is required

 _{Design, method used to choose the sample from the} population

 _{Poor designs lead to misleading data}

 _{Use a sample size LARGE enough so that we can see the true}

nature of any effects.

Sampling

 _{Voluntary Response Sample, People who choose} themselves by responding to a general appeal (People make the choose to respond to the survey)

Problems: • Biased

• Strong (usually negative) opinions are most likely to respond

 _{Selected (convenience) Sampling: People are selected} for the sample based upon the discretion of the person

creating the sample

 _{Bias, when the method used to obtain results in systemic} favor a particular outcome (either consistently too high or consistently to low)

 _{The goal of every sampling technique/survey Unbiased,}

without systematic favor or weight

Common types of Biased…

1. Under-coverage/Selection bias, when the method for selecting the participants in a sample do not represent the population of interest. Somebody was LEFT OUT of the

sample

 _{Mall bias – if shoppers at a mall are surveyed to determine}

attitudes about raising the sales tax, the results are not likely to represent all area residents

2. Nonresponse/Nonparticipation bias, when a representative sample is chosen for a survey but a subset cannot be contacted or does not respond

 _{Phone bias – phoning people at home in the evening would omit}

people who work during that time. Their opinions would not be represented

3. Response Bias, when the responses of those surveyed are swayed in way direction or the other

 _{Wording of the question}  _{Order of choices}

 _{Demeanor or appearance of the interviewer}  _Honesty

•

_{LARGER RANDOM SAMPLES GIVE MORE}

ACCURATE RESUSLTS THAN SMALLER

SAMPLES

Sampling: How we select people for a survey

1. Simple Random Sample (SRS)

 _{People are selected at random (draw names, computer}

program, random digits table)

 _{Gives each individual an equal chance but also gives every}

possible sample an equal chance to be chosen

These other three random sampling designs give each individual an equal chance but not each sample

2. Stratified Sample

 _{People are put into groups of similar characteristics (Age,}

Gender, Ethnicity, Income…) known as Strata

 _{THEN choose a separate SRS in each stratum and combine}

the SRS’s to form a full sample

Sampling: How we select people for a survey

3. Systematic Sample

 _{Every n}th person is selected

4. Clustered Sample

 People are grouped by convenience (known as clusters) and then randomly select some of the clusters for your sample.

 _{Typically people are grouped by geographic regions}

Multistage Sampling Design

 _{Choosing smaller samples in stages resulting in a sample}

consisting of clusters of individuals. Each stage may include a SRS, stratified sample, or another type of sample

 _{Example: when testing a shipment of goods I might randomly}

select one box of items and then from that box randomly select which item will be inspected

 _Or:

1. The US is divided in 2000+ Geographic Areas

2. Each area is divided into small “neighborhood” areas stratified using ethnic or other information

3. Each neighborhood is clustered into groups of

households that can be easily reached for an opinion poll or survey