Sec 1.1 Sampling

Vocabulary:

1.Statistics

Statistics is the study of procedures(操作) for collecting,describing and drawing conclusions from data.

2.Population

A population is the entire collection of individuals about what information is sought.

3.Sample

A sample is a subset(子集) of a population.

4.Statisic

A statistic is a number that describes a sample.

5.Parameter

A parameter is a number that describes a population.

Types of Sampling:

1.Simple Randon Sampling(SRS)

A sample collected such that each collector of n item from a population is equally likely to be chosen,usually done by computer.

p.s. n = sample size

2.Stratified Sampling

Population is first divided into subgroups called "strata"(地层).Then,some individuals are selected from each subgroup in a random fashion(方式).

3.Cluster Sampling

Population is first divided into subgroups called "Cluster".Then,some subgroups are randomly selected and all members of selected subgroups are chose.

4.Systematic Sampling

Population is ordered.Then select every Kth individual. (K大于等于2)

5.Convenience Sampling

A sampling is chosen with no defined(界定的) method.Only ok if you can believe your sample is really reflective of your population.

6.Voluntary Response Sampling(VRS)

A news commentator asks people to call,In radio station,Surveys on ineternet.

(No Random)

Example:

1. To conduct a pre-election opinion poll on a proposed amendment to the state constitution, a random sample of 10 telephone prefixes (first three digits of the phone number) was selected, and all households from the selected phone number was selected,and all the households from the selected phone pretixes were called.

Cluster Sampling

2. A construction engineer has just received a shipment of 2000 concrete blocks, each weighing approximately 50 pounds. The blocks have been delivered in a large pile. The engineer wishes to test the crushing strength of the blocks so she takes 10 blocks of the top of the pile and tests them for crushing strength.

Convenience Sampling

3. To maintain quality control in a brewery, every 20th bottle of beer coming off the production line was opened and tested for purity.

Systematic Sampling

4. Foothill students were assigned numbers. Then, 50 numbers were randomly generated by a computer. The students who correspond to these numbers were interviewed about campus life.

Simple Random Sampling

5. To judge the appeal of a proposed television sitcom, a simple random sample of 10 people from each of three different age categories was selected and those chosen were asked to rate a pilot show.

Startified Sampling

6. A radio talk how host invites listeners to call in and express their opinions on foreign policy.

Voluntary Respond Sampling

Sec 1.2 Types of Data

Vocabulary:

1.Individuals

People or things from which we collect information.

2.Variable

Charcteristics of the individuals about which we collect information.

3.Qualitative Variables

Classify indivduals into categories.(Not numerical)

4.Quantitative Variables

Numerical variables that tell how much or how many of something there is.

5.Data

Values of ratable (可估价的).

Levels of Measurement

QUALITATIVE:

1.Nominal

Qualitative variables whose categories have no natural ordering

2.Ordinal

Qualitative variables whose categories have a natural ordering

QUANTITATIVE:

3.Discrete

Quantitative data whose values can be listed.(List could be infinite)

4.Continuous

Quantitative data whose values are measurable over an internal(间隔).

Example:

1. Which are qualitative and which are quantitative?

a. A student's major

QUALITATIVE

b. The number of hours a student typically studies per week

QUANTITATIVE

2. Which are nominal and which are ordinal?

a. A student's country of origin

NOMINAL

b. A student's grade in statistics class

ORDINAL

3. Which are discrete and which are continuous?

a. The number of units a student is taking

DISCRETE

b.A student's height

CONTINUOUS