Final PPt of Sampling

8/4/2019 Final PPt of Sampling

1/17

Population & Sampling


2/17

Population

Population refer to the entire groupof people,events,or things of interestthat the researcher wishes toinvestigate.


3/17

Element

An element is a single member ofthe population.


4/17

Sampling Frame

The population frame is a listing ofall element in the population fromwhich the sample is drawn


5/17

Sample

A sample is a subset of the

population. it comprise somemember selected from it

Target Population

Sample


6/17

UNIT

A unit is a single member of thesample, just as an element is a singlemember of the population


7/17

Why Sample?

Lower Cost.

Greater Accuracy of result.

Greater speed of data collection.


8/17

What is a Good Sample?

Validity of a sample depends on twoconsideration

Accuracy

Precision


9/17

Steps In Sampling Design

What Is Target Population?

What are the parameter of interest?

What is sampling frame? What is the appropriate sampling

method?

What size sample is needed?


10/17

Normality Of Distribution


11/17

Sampling Method

Probability

Nonprobability


12/17

Probability

Simple Random

Complex Random

Systematic Stratified

Cluster

Double


13/17

Nonprobability

Convenience

Purposive

JudgmentQuota

Snowball


14/17

The Problem Of Non-Responce

You can randomly pick elements from sampling

frame and use them to randomly select people

But you cannot make people respond

Non-response destroys the generalize ability of the

sample. You are generalizing to people who arewilling to respond to surveys

If response is 90% or so, not so bad. But if it is

50%, this is a serious problem


15/17

Errors in sample surveys

Survey results are typically subjectto some error. Total errors can beclassified into sampling errors and

non-sampling errors. The term"error" here includes systematicbiases as well as random errors


16/17

Sampling errors

Sampling errors are induced by the sampledesign. They include:

Selection bias

When the true selection probabilities differfrom those assumed in calculating the results.

Random sampling error

Random variation in the results due to the

elements in the sample being selected atrandom.
http://en.wikipedia.org/wiki/Selection_biashttp://en.wikipedia.org/wiki/Sampling_errorhttp://en.wikipedia.org/wiki/Sampling_errorhttp://en.wikipedia.org/wiki/Selection_bias


17/17

Non-sampling error

Non-sampling errors are caused by other problems in datacollection and processing. They include:

Overcoverage Inclusion of data from outside of the population.

Undercoverage

Sampling frame does not include elements in the population. Measurement error E.g. when respondents misunderstand a question, or find it

difficult to answer.

Processing error Mistakes in data coding.

Non-response Failure to obtain complete data from all selected individuals.

Documents

Final PPt of Sampling