Whether it is in Natural Science or Social

Science , most of the students will have to do a project or assignment using some kind of research

In the research process, sampling and data collection is one of the vital components

This presentation will provide an introduction to various sampling methods that one could adopt in research in Social as well as Natural Sciences

Process The sampling process comprises several stages:

Defining the population of concern Specifying a sampling frame, a set of items or events

possible to measure Specifying a sampling method for selecting items or

events from the frame Determining the sample size Implementing the sampling plan Sampling and data collecting Reviewing the sampling process

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PopulationAll subjects (items/people) having the characteristic

the researcher wishes to understand.As the time and resources are limited to get

information from all, it is required to identify a subset or a representative sample of that population.

Sampling FrameThe sample which we believe to have the

elements/properties we are looking forIs representative of the population

SamplingA sample is a smaller but representative collection of

units from a population to determine the truths about the population

Why sampleAs time, resources and work are limited need to work

on something manageable but representative

Methods of data collectioni. Measurementsii. Observations ( non- interviews)iii. Personal interviews

iv. Type- structured or unstructuredv. Approach – direct or indirect

vi. Telephone interviewsvii. Mailing questionnaires

Types of SamplingQuantitative sampling

Sampling of biological material Plots, transects, quadrats etc.

Qualitative sampling Surveys, questionnaires, discussions, observations etc.

Sampling tools in biological data collection

Quadrat Sampling

Transect Sampling

Some methods used in sociological data collection

Surveys

Key informant interviews

Preparation of a questionnaire with different categoriesI. Quantity or informationII. In which year did you receive the membership of Knuckles

Environment Society?III. CategoryIV. Have you ever been or are you now involved in conservation

activities for the nature?V. 1.Yes(currently) 2.yes (in the past) 3.Never

VI. List or multiple choicesVII. Do you think the time spend on nature protection programs as any

of the following?1.A must 2.a necessity 3.a right 4.an investment

5.Waste of time 6.non of these

iv. ScaleHow would you describe your parents’ attitude to nature protection programs?1.Very positive 2.positive 3.mixed/neutral 4.negative

5.very negative 6.not sure

v. Ranking

What do you see as the main purpose of your nature protection activities? Please rank all these relevant in order from 1.

Personal development/career development/ subject interest/ recreation/ fulfill ambition /keeping stimulated /other

vi. Complex grid/tableHow would you rank the benefits of your study for each of the following. Please rank each item.

For Very positive

Positive Neutral

Negative

Very negative

Not sure

you

Your family

Your employer

country

community

Vii. Open endedWe would like to hear from you if you have any further

comments.

Ethical issues in data collectionEthical issues concerning the participants….

I.Collecting information (time wasting)II.Seeking consentIII.Providing incentivesIV.Seeking sensitive informationV.Possibility of causing harm to the participantsVI.Maintaining confidentiality

Ethical issues in data collectionEthical issues relating to the researcher….i.Avoiding biasii.Provision of deprivation of a treatmentiii.Using inappropriate research methodologyiv.Incorrect reportingv.Inappropriate use of information

What is your population of interest?

To whom do you want to generalize your results?

All doctorsSchool childrenAll CanadiansAll Women aged 15-45 yearsOther

19SAMPLING BREAKDOWN

SAMPLING…….

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TARGET POPULATION

STUDY POPULATION

SAMPLE

Types of SamplingProbability SamplingEvery unit in the population has a chance of being

selected in the sampleAll sample units are given same weightAlso known as equal probability of selection

Non Probability SamplingSome elements of the population have no chance of

selection hence non random samplingSampling is done based on a predetermined criteria

Non probability sampling includesAccidental SamplingQuota SamplingPurposive Sampling

ExampleWe visit every household in a given street,

and interview the first person to answer the door. In any household with more than one occupant, this is a nonprobability sample, because some people are more likely to answer the door (e.g. an unemployed person who spends most of their time at home is more likely to answer than an employed housemate who might be at work when the interviewer calls) and it's not practical to calculate these probabilities.

Types of Samples

Probability (Random) SamplesSimple random sample

Systematic random sampleStratified random sampleMultistage sampleMultiphase sampleCluster sample

Non-Probability SamplesConvenience samplePurposive sampleQuota

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SIMPLE RANDOM SAMPLING• Applicable when population is small, homogeneous

& readily available• All subsets of the frame are given an equal

probability. Each element of the frame thus has an equal probability of selection.

• It provides for greatest number of possible samples. This is done by assigning a number to each unit in the sampling frame.

• A table of random number or lottery system is used to determine which units are to be selected.

• Estimates are easy to calculate.25

SIMPLE RANDOM SAMPLING contd……..

Disadvantages

If sampling frame large, this method impracticable.Minority subgroups of interest in population may not be present in sample in sufficient numbers for study.

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SYSTEMATIC SAMPLINGSystematic sampling relies on arranging the

target population according to some ordering scheme and then selecting elements at regular intervals through that ordered list.

Systematic sampling involves a random start and then proceeds with the selection of every kth element from then onwards. In this case, k=(population size/sample size).

A simple example would be to select every 10th name from the telephone directory (an 'every 10th' sample, also referred to as 'sampling with a skip of 10').

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SYSTEMATIC SAMPLING……

ADVANTAGES:Sample easy to selectSuitable sampling frame can be identified

easilySample evenly spread over entire reference

populationDISADVANTAGES:Sample may be biased if hidden periodicity in

population coincides with that of selection.Difficult to assess precision of estimate from

one survey.29

Stratified SamplingThe sampling frame is organised into pre determined

strataSampling is done within the strata as an independent

sub populationIndividual elements are randomly selected within itAs each stratum is treated as independent population

different sampling approaches can be applied to different strata.

Advantages Ensures proportionate representation of the sample E.g.. If we want to represent the minority sub groups adequately

this can be done by this Drawbacks

When there are many strata to be used, the sampling size per group may be larger than other methods

Stratifying variable may be related to some but not to others and may lead to complications

If equal no of samples taken from all the stratified groups, less representative ones could be over sampled if not careful.

STRATIFIED SAMPLING…….

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Draw a sample from each stratum

CLUSTER SAMPLINGCluster sampling is an example of 'two-stage

sampling' . First stage a sample of areas is chosen Second stage a sample of respondents within

those areas is selected. Population divided into clusters of homogeneous

units, usually based on geographical contiguity.Sampling units are groups rather than individuals.A sample of such clusters is then selected.All units from the selected clusters are studied.

Cuts down on the cost of travel and other administrative costs

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Difference Between Strata and ClustersAlthough strata and clusters are both non-

overlapping subsets of the population, they differ in several ways.

All strata are represented in the sample; but only a subset of clusters are in the sample.

With stratified sampling, the best survey results occur when elements within strata are internally homogeneous. However, with cluster sampling, the best results occur when elements within clusters are internally heterogeneous

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ActivityIn estimation of immunization coverage in a

province, data on seven children aged 12-23 months in 30 clusters are used to determine proportion of fully immunized children in the province.

Give reasons why cluster sampling is used in this survey.

Non Probability Sampling methods

CONVENIENCE SAMPLINGSometimes known as grab or opportunity sampling or accidental

or haphazard sampling. A type of nonprobability sampling which involves the sample being

drawn from that part of the population which is close to hand. That is, readily available and convenient.

The researcher using such a sample cannot scientifically make generalizations about the total population from this sample because it would not be representative enough.

For example, if the interviewer was to conduct a survey at a shopping center early in the morning on a given day, the people that he/she could interview would be limited to those given there at that given time, which would not represent the views of other members of society in such an area, if the survey was to be conducted at different times of day and several times per week.

This type of sampling is most useful for pilot testing. In social science research, snowball sampling is a similar technique,

where existing study subjects are used to recruit more subjects into the sample.

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CONVENIENCE SAMPLING…….

Use results that are easy to get

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QUOTA SAMPLING The population is first segmented into mutually exclusive

sub-groups, just as in stratified sampling. Then judgment used to select subjects or units from

each segment based on a specified proportion. For example, an interviewer may be told to sample 200

females and 300 males between the age of 45 and 60.It is this second step which makes the technique one of

non-probability sampling. In quota sampling the selection of the sample is non-

random. For example interviewers might be tempted to interview

those who look most helpful. The problem is that these samples may be biased because not everyone gets a chance of selection. This random element is its greatest weakness and quota versus probability has been a matter of controversy for many years

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Judgmental sampling or Purposive sampling- The researcher chooses the sample based on

who they think would be appropriate for the study. This is used primarily when there is a limited number of people that have expertise in the area being researched

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PANEL SAMPLING (Time Series) Method of first selecting a group of participants through a

random sampling method and then asking that group for the same information again several times over a period of time.

Therefore, each participant is given same survey or interview at two or more time points; each period of data collection called a "wave".

This sampling methodology often chosen for large scale or nation-wide studies in order to gauge changes in the population with regard to any number of variables from chronic illness to job stress to weekly food expenditures.

Panel sampling can also be used to inform researchers about within-person health changes due to age or help explain changes in continuous dependent variables such as spousal interaction.

There have been several proposed methods of analyzing panel sample data, including growth curves.

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Selecting sample sizesSelecting sample size is a function of

Study goalsDegree of precision requiredDesign typeBudgetOther (ethical etc.)

Selecting the sample sizeA simple formula for this is as follows;

n = N/1+N*(e)2

Wheren=sample sizeN = population size e=the confidence level we like to work with (eg. If it is

95% then the error is 5% (0.05); if it is 99% then the error is 1% (0.01)

The larger the population variability larger the sample size to get an accurate reading

If the population is mostly homogenous the sample size can be small

Example:It is required to identify a presence of a disease in a

population. The number of the population that we need to get information is 2500. We would like to have the confidence level is 95%. Then the sample size would be

N=2500/1+ (2500)*(0.05)2

=344

Eg. Investigating the level of biodiversity in a natural forestsUsing either plots or transects, the sampling needs to

be increased until the number of plant species becomes no more

Describe physical/biological and sociological experiments separately taking some examplesFor examplesBiological experiments – can show how to use the

plots/transects and give reasons for using them – this is for non moving objects such as plants.

For moving objects – circular plots with time series observations

For social experiments – other methodologies can be used such as interviews, observations, key informant surveys, focal groups discussions etc. – elaborate this

CheersMaxwell

maxran1@yahoo.com