Sections 2.3 – 2.6

RecapUnit Test on

Tuesday, October 2, 2012

2.3 Sampling Techniques

Scenario:

A sample of young adults were surveyed regarding their diets.

If the sample consists of young adults, then who is the population of this study?

Scenario:

A sociology professor talks to every 9th elementary school student walking into the local library about their reading skills. If he interviewed 34 people, what is the population size?

A sociology professor talks to every 9th elementary school student walking into the local library about their reading skills. If he interviewed 34 people, what is the population size?

interval = pop. size / sample size

Re-arrange it to get

pop. size = interval x sample size = 9 x 34 = 306 elem. school students

Was that an example of systematic sampling or stratified

sampling?

Sample Types

Sample

Simple random sample

Systematic sample

Stratified sample

Sample Types Cluster sample –

Multi-stage sample

Voluntary-response sample

Convenience sample

Sample Types Cluster sample - the total population is

divided into groups (or clusters) and a simple random sample of the groups is selected.

Multi-stage sample

Voluntary-response sample

Convenience sample

Sample Types Cluster sample - the total population is

divided into groups (or clusters) and a simple random sample of the groups is selected. *My drawing on the white board was not a definition, it was only describing the textbook’s fast-food chain example.

Multi-stage sample -

Voluntary-response sample

Convenience sample

Sample Types Cluster sample - the total population is

divided into groups (or clusters) and a simple random sample of the groups is selected. *My drawing on the white board was not a definition, it was only describing the textbook’s fast-food chain example.

Multi-stage sample – several levels of random sampling

Voluntary-response sample –

Convenience sample

Sample Types Cluster sample - the total population is

divided into groups (or clusters) and a simple random sample of the groups is selected. *My drawing on the white board was not a definition, it was only describing the textbook’s fast-food chain example.

Multi-stage sample – several levels of ran. sampling

Voluntary-response sample – researcher invites any member of population into survey

Convenience sample

Sample Types Cluster sample - the total population is

divided into groups (or clusters) and a simple random sample of the groups is selected. *My drawing on the white board was not a definition, it was only describing the textbook’s fast-food chain example.

Multi-stage sample – several levels of ran. sampling

Voluntary-response sample – researcher invites any member of population into survey

Convenience sample

Sample Types Cluster sample - the total population is divided

into groups (or clusters) and a simple random sample of the groups is selected. *My drawing on the white board was not a definition, it was only describing the textbook’s fast-food chain example.

Multi-stage sample – several levels of ran. sampling

Voluntary-response sample – researcher invites any member of population into survey

Convenience sample - sample selected but it’s easily accessible

Question A community centre chooses 15 of its

members and asks them to have each member of their families complete a short questionnaire.

A) What type of sample is the community centre using?

Question A community centre chooses 15 of its

members and asks them to have each member of their families complete a short questionnaire.

A) What type of sample is the community centre using?

Answer: Cluster Sample

Question A community centre chooses 15 of its

members and asks them to have each member of their families complete a short questionnaire.

B) Are the 15 community-centre members a random sample of the community?

Question A community centre chooses 15 of its members

and asks them to have each member of their families complete a short questionnaire.

B) Are the 15 community-centre members a random sample of the community?

Answer: No, not every member has an equal chance of being selected

Question A community centre chooses 15 of its

members and asks them to have each member of their families complete a short questionnaire.

C) To what extent are the family members randomly chosen?

Question

A community centre chooses 15 of its members and asks them to have each member of their families complete a short questionnaire.

C) To what extent are the family members randomly chosen?

Answer: to the same extent as the member of the community was selected

2.4 Bias in Surveys Sampling Bias

Non-response Bias

Measurement Bias

Response Bias

2.4 Bias in Surveys Sampling Bias – sample doesn’t rep. population

Non-response Bias – groups under-represented in survey b/c they chose not to participate

Measurement Bias – data collection method misestimates population characteristics

Response Bias – false/misleading answers given because of sensitive survey questions

Intentional bias –

Unintentional bias –

Leading questions –

Loaded questions -

Intentional bias – used to manipulate stats in favour of a certain point of view

Unintentional bias – can be introduced if sampling and data collection methods are not chosen carefully

Leading questions – can give suggested answers which causes a bias

Loaded questions – contains wording or information intended to influence respondents’ answers

Any bias below?

Can the proposed record level of

healthcare expenditures be justified in

view of the enormous deficits facing the

Canadian people and the pressing social

needs that are currently unmet?

2.5 Measure of Central Tendency

What does the above mean?

2.5 Measure of Central Tendency

What does the above mean?

values around which a set of data tends

to cluster

What is the difference between and ?

What is the difference between and ? refers to mean of population

refers to mean of sample

What is the difference between and ?

Hand back quizzes & … Exercise: Calculate mean quiz mark with

proper weights

Knowledge/Understanding 40%

Application 30%

Communication 10%

Thinking 20%

Grade 10 Exam Question on Determining the Centroid

Grade 10 Exam Question on Determining the Centroid

x mean = (1+3+5)/3 = 3

y mean = (2+4+0)/3= 2

centroid = (3, 2)

You can calculate x mean, y mean & z mean to get centroid of 3D objects

Grade 10 breaks down when weights are applied. Consider bottom right vertex mass = 2.2 kg top vertex mass = 5.7 kg left vertex mass = 0.2 kg Determine the center of the mass

x mean = [1(0.2)+3(5.7)+5(2.2)] / (0.2 + 5.7 + 2.2) = 3.5

y mean = [2(0.2)+4(5.7)+0(2.2)] / (0.2 + 5.7 + 2.2) = 2.9

Grade 10 breaks down when weights are applied. Consider bottom right vertex mass = 2.2 kg top vertex mass = 5.7 kg left vertex mass = 0.2 kg Determine the center of the mass

2.6 Measures of Spread

We’ll do this tomorrow

Review Questions Q #1, 5, 6, 7, 9, 11, 14

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