RESEARCHSAMPLING DESIGNS

(PA 298 Research for Social Science)

Presented by:Mr. John Ladaran

March 12, 2011

Presented to:Maria Theresa P. Pelones, DM

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Sampling: The process of obtaining information from a subset

(sample) of a larger group (population) (webster 1985)

The act, process, or technique of selecting a suitable sample, or a representative part of a population for the purpose of determining parameters or characteristics of the whole population. (Mugo, Fridah)

used to make inferences about a population from a relatively small number of observations, that are assumed to be representative of the population.

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Purpose of Sampling:To draw conclusions about populations from

samples

To accurately describe the parameters of a population based on the description (statistics) of a set of elements drawn from the population.

make generalizations about the whole [the population] which are valid [accurate] and which allow prediction. If this spoonful needs salt, then it's likely that this would be true for others as well.

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Terminologies:Population

* The entire group of people of interest from whom the researcher needs to obtain information

Sample

* contacting a portion of the population (e.g. 10%)Census

* the entire populationElement

* one unit from a population

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Two keys to be considered:1.) Selecting the right people

Have to be selected scientifically so that they are representative of the population

2.) Selecting the right number of the right people

To minimize sampling errors

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Principles of samplingTwo keys:

1.) Selecting the right people

- have to be selected scientifically so that they are representative of the population

2.) Selecting the right number of the right people

- to minimize sampling errors

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Principles of sampling

Measure the sample using statistics in order to draw inferences about the population and its parameters

populationsample

Population

sample

parameters

statistic

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Principles of samplingCharacteristics of good samples

Truly RepresentativeAccessibleLow costOptimum sizeResult can be applied universally with

reasonable level of confidenceSimilar to population

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Principles of sampling

sample

population

sample

population

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Advantages & DisadvantagesSampling saves time and

moneySampling saves labor.A sample coverage permits

a higher overall level of adequacy than a full enumeration.

Complete census is often unnecessary, wasteful, and the burden on the public.

•There is room for potential bias in the selection of suitable subjects for the research. This may be because the researcher selects subjects that are more likely to give the desired results, or that the subjects tend to select themselves.

•Sampling requires a knowledge of statistics, and the entire design of the experiment depends upon the exact sampling method required.

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Processes of Sampling Design1.) Define the population

2.) Identify the sampling frame

3.) Select a sampling design or procedure

4.) Determine the sample size

5.) Draw the sample

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Processes of Sampling Design

Determine sampling frame

Non-Probability Sampling

Probability Sampling

Sample Size

Execute sampling design

Determine sampling procedure

Define Population

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1.) Define the Target PopulationIt addresses the question “Ideally, who do you want

to survey?”

It involves

- defining the population units

- setting population boundaries

- screening

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2) Determine the sampling Frame Obtaining a list of population (how will you reach

sample)

Problems with lists

- omissions

- ineligibles

- duplications

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3.) Selecting a Sampling Design Probability Sampling

- equal chance of being included in the sample

Non-probability Sampling

- unequal chance of being included in the sample

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4.) Sample SizeHow large a sample should be?

Sample size constrains:depends on the nature of the analysis to be

performedDesired precision of the estimatesKind and number of comparisonsNumber of variables that have to be examinedHow heterogeneous a population is sampled.

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Determination of Sample sizeNature of population

-heterogeneous or homogenous

-dispersion variabilityNumber of variables to be studiedNature of groups and sub-groups proposedNature of study (quantitative or qualitative)

-intensive & continuous or general surveyType of sampleIntended depth of analysis

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Determination of Sample sizePrecision and reliabilityLevel of non responseAvailable finance and other resourcesSize of populationNature of size of populationSize of questionnaire

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to be continue by….

MS. CHONA CASANOVA

ON DIFFERENT TYPE OF SAMPLING DESIGN