Methods Of Research

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METHODS OF RESEARCH Res. 1E METHODS OF RESEARCH Res. 1E

Ana L. Vargas RESEARCH METHODOLOGY Assistant Professor 2

Prof. Ana L. Vargas

Research Methodology

Sampling

Sampling 

Process of selecting a required number of individuals from the study population so as to focus on the sample and not in the whole population.



Principle of sampling 

To get the maximum information about the population with minimum effort and with limited resources

Why do we need Sampling 

Studying the entire population is difficult.



It will be costly, time consuming and not feasible



Studying the whole population is impossible and unnecessary.



If sampling is done properly:  Accurate and reliable estimates can be made  More details/characteristics can be collected  Can get best results in least possible time  Project management is easy

Characteristics of Sampling 

Representativeness



Unbiased selection



Adequacy of sample.

Characteristics of Sampling 

Representativeness 



Sample has all the important characteristics and similar distribution

Unbiased selection 

Underrepresented or overrepresented members of the population 



Due to faulty selection of sample ot faulty demarcation of sampling units

Adequacy of sample. 

Results in reduction cost and saves time

Advantages of Sampling 

Provides a more comprehensive information.



Saves time and effort.



Provides a wider scope of study and interests.



Accurate with the data gathered in total population.

Sampling terms 

Population (universe) 



Group of individuals or units possessing certain predetermined characteristics intended for the study.

Representative sample 

It has all the characteristics with similar distribution as that of the population from which it is drawn

Sampling terms 

Sampling frame 



It is the list of all elements (persons, households, objects, specific events or units) in the population. e.g. voter’s list

Sampling unit 

the constituent elements of a population which are to be sampled from the population and cannot be further subdivided for the purpose of sampling at a time. e.g. town, village, district

Sampling terms 

Sampling fraction 



Sample size 



Proportion of population that is included in the sample. e.g. 20% the number of units in a sample

Sampling error 

Any type of bias that is attributable to mistakes in either drawing a sample or determining the sample size

Sampling 

Applicable to studies with very high population.



Uses the whole population as the source of information.



The study is tedious and impractical for it wastes a lot of time, effort and money if data will be gathered to all population.

Population 

Population is a group individuals to which the study is applied.



Population is limited by place or locality



Population describes who your population.



Examples   

All students at Partido State University. Government employees in the Bicol Region Teachers teaching science in public high schools in the Division of Camarines Sur

Three Types of Population 

Target Population - the actual population to which the researcher is unable to generalize.



Accessible (source)Population is the population in which the researcher can make a generalization.



Sampling (study) Population is the population from which the sample will be actually taken as determined by the sampling frame.

Population Distribution

Illustration #1 

Problem: The effects of Computer Aided Instruction to the Academic Performance of Students in Chemistry. 

Target Population: All Chemistry students.



Accessible Population: All Chemistry students at PSU.



Sample Population: Ten percent (10%) of the total Chemistry students at PSU.

Illustration #2 

The Attitudes and Perceptions of Public School Teachers Towards In Service Trainings and Seminars. 

Target Population: All Public School Teachers



Accessible Population : All Public School Teachers in the Division of Camarines Sur



Sample Population: Two hundred fifty school teachers selected from the division of Camarines Sur.

Sample vs. Population

Population

Sample

Two Types of Sampling 

Random Sampling (Probability)



Non random sampling-

Random (probability) Sampling 

Random Sampling (Probability) 

 



every member of the population are given equal chance of being selected.

Best among all the methods Most powerful statistical analysis on the results can be done subsequentlyCan be done by drawing lots to avoid bias.

Random (probability) Sampling 



Include: 

Simple random sampling (unrestricted)



Systematic random sampling (quasi-random)



Stratified random sampling



Cluster sampling (area sampling)



Multistage sampling

Important and frequently used methods

RANDOM SAMPLING

Simple Random Sampling

Simple Random Sampling     

Define the study population ( N ) Prepare a proper sampling frame (n) Determine the sample size Select the required number of samples Done by :  



Lottery method – small population Random number method – by using standard tables ( Tippet’s table, Fisher and Yate’s table and Kendall and Smith’s table ) Computer generated random numbers

Lottery Procedure 1. Write down the name of each member of the population on pieces of paper. 2. Place these papers in a box or a container drum.

3. The box or lottery drum must be shaken thoroughly to prevent some pieces of paper from sinking at the bottom. 4. Picked the required number of sampleunits from the lottery drum.

Simple Random Sampling 

Example Population

1 6 11 16

2 7 12 17

3 8 13 18

4 9 14 19

Sample

5 10 15 20

3

6

9

12 15 18

Advantages   

 



Personal bias is eleminated Representative of a homogenous population No need for thorough knowledge of the units of population Accuracy of the sample can be tested Used in other methods of sampling

Disadvantages    

Cannot be used for large population When there is large difference between units Cost and time of collection of data are more Logistically more difficult in field conditions

Systematic Random Sampling

Systematic Random Sampling   

   

Simple & convenient way of selecting a sample Requires less time and cost Sample is spread evenly over entire reference population Can be used in infinite population requires sampling frame Units are selected at an uniform interval Useful when information is collected from units which are in serial order (i.e.) entries in register, house in blocks etc.

Systematic Random Sampling 

Done by: 

Identify the sample size (n)



Put the population in sequential order & number them serially – sampling frame



Identify total no.of units in the population (N)



Divide N/n = sampling interval (k)



Identify a random no.which is less than or equal to ‘k’



Select every n’th item starting with a random one

Stratified Random Sampling

Stratified Random Sampling (SRS) 

Dividing the population into subgroups or strata - stratification



Units within the stratum are homogenous and between the strata are heterogeneous



From each stratum a simple random sample is selected and combined together to form the required sample from the population

Two types of SRS 

Proportional stratified random sampling 



Unequal size

Disproportionate stratified random sampling 

Equal size

Proportional stratified sampling • cases are drawn from each strata in proportion to their prevalence in the population.

Advantages of SRS 



  

Every unit in the stratum has the same chance of being selected More representative Ensures proportionate representation Greater accuracy Greater geographical concentration

Disadvantages of SRS 



Division of population into strata needs more money, time and statistical experience Improper stratification leads to bias – if there is overlapping of strata



Certain Subgroups or strata are selected. Strata

Population

%

Sample Size

Upper Class

200

30%

60

Middle Class

400

40%

160

Lower Class

200

30%

60

Learning check A survey to find out if families living in a certain municipality are in favor of Charter change will be conducted. To ensure that all income groups are represented, respondents will be divided into high income (class A), middle-income (class B) and low income (class C). Strata High- income (Class A) Middle-income Cclass B) Low-income (Class C)

No. of families 1 000 2 500 1 500 N= 5 000

Learning check 1. Using a 5% margin of error, how many families should be include in the sample? 2. Using proportional allocation, how many from each group should be taken as samples? 3. Using equal allocation, how many from each group should be taken as samples?

Learning check Strata

No. of families

Class A

1 000

Class B

2 500

Class C

1 500 N= 5 000

Proportional Equal allocation allocation (%)

Cluster Sampling 

The whole population is divided into groups called clusters.



Each cluster is representative of the population



Clusters are selected randomly



A random sample is then is taken from within each cluster



Lot of clusters are sampled so that the results can be generalized for whole population

Cluster Sampling 

Clusters should be as small a possible consistent with the time & cost limitations



No. of units in each cluster must be more or less equal

Advantages 





Cuts down the cost of preparing sampling frame and cost of travelling between selected units Eliminates the problem of “packing”

Disadvantages 



Sampling errors is usually higher than for a simple Random sample of the same size

Cluster Sampling Example WHO 30 clusters for coverage evaluation survey  Pulse polio immunization coverage evaluation survey In a PHC estimate the proportion of infants with age 6 months to 1 yr who are fully immunized . 

Cluster Sampling Example In a PHC estimate the proportion of infants with age 6 months to 1 yr who are fully immunized . 1. Identification of total population and the geographical area 2. Identification of age group to be included 3. Listing of all villages 4. Tabulation



Cluster Sampling Selection of groups or clusters of subjects rather than individuals A A

B

C C

Population E D

E

F Sample

Cluster sampling

Learning check 

You want to determine the average expenses of families living in the province of Camarines Sur. In sum, there are 208 Brgys. In four districts of Camarines Sur. What should be the sample size?

Multi-Stage sampling 

Used for large and diverse populations (eg) nation, region or state



Usually carried out in phases



Involves more than one sampling methods



Example : Estimating the problem of Iodine deficiency disorders in India

Multi-Stage sampling 

First stage : few states are randomly selected



Second stage : few districts from above states



Third stage : few blocks from above districts



Fourth stage : few villages from above districts



Fifth stage : few households from each village

Multi-Stage sampling ADVANTAGES :  Sample frame for individual units not required  Cuts down the cost of preparing sample frame DISADVANTAGES :  final sample may not be representative of the total population  Sampling error is increased, when compared with simple random sampling

Multi-Stage Random Sampling 

A combination of cluster random with simple random sampling. ABC

DEF

GHI

DEF KLM

KLM

NOP

QRS

QRS

ELR

NON-PROBABILITY SAMPLING

Non-Random Sampling 

Does not provide equal chance for every member to be selected.



May lead to unrepresentative samples



It lacks accuracy in view of selection bias



May not represent the population well



Used when there is no sample frame for the population



Mostly used in qualitative research like exploratory research, opinion surveys and marketing studies

Non-Random Sampling 

Include: 

Purposive sampling (judgemental sampling)



Convenience sampling (oppurtunity sampling)



Quota sampling



Expert opinion sampling



Snowball sampling (chain sampling, chain referral



sampling or referral sampling)

Non-Random Sampling 

Include: 

Purposive sampling (judgemental sampling)



Convenience sampling (oppurtunity sampling)



Quota sampling



Expert opinion sampling



Snowball sampling (chain sampling, chain referral



sampling or referral sampling)

Convenience(Accidental) Sampling 

Accidental, opportunity, accessibility or haphazard sampling



Use of readily available persons for the studysample of convenience



Stopping people in a street corner, people select themselves in response to public notices-risk of bias is greater.



Lack of representativeness



Used for making pilot studies

Purposive Sampling 

Judgmental sampling



Researchers knowledge about the population can be used to hand-pick sample members, knowledgeable about the study



Used in newly developed instruments can be pretested and evaluated

Quota Sampling 

Researcher utilizes knowledge about the population – representativeness into the sampling plan



Population is divided into quotas – age, socioeconomic status, religion etc.



Number of units within each quota –personal judgment of the investigator.



Used by quantitative researchers



Used in public opinion studies

Example

Snowball Sampling 

Network or chain/referral sampling



Research population of specific traits-difficult to identify



Early sample members asked to refer other people who meet eligibility criteria



Sampling hidden populations-homeless or IV drug users-respondent driven sampling (rds),variant of snow ball sampling

Choice of Sampling method 

Method



Best when



Simple random sampling



Whole population is available



Stratified random sampling



When specific subgroups are to be investigated

Choice of Sampling method 

Method 



Systematic random sampling

Cluster sampling



Best when 

When stream of representative people are available



When population groups are separated & access to all is difficult

SAMPLE SIZE

Sample size 

Percentage



Specific Margin of Error



Formula

Use of percentage Population

Percentage

Sample

100

100

100

200

70

140

300

50

150

400

35

150

500

30

150

600

25

150

700-10,000

20

140-2000

11,000-15,000

15

1,650-2,250

16,000 and above

10

1,600-above

Rivera, 1999

Use of Formula 

Sloven Formula n = N/1 + Ne2 Where: n = sample size N = population size e2 = margin of error raised to the second power



Percentage Rs = n/N 

Where: Rs = representative sample for a group  N = Population size  n = computed sample size

Example 

Use of specific margin of error Population

Margin of Error

500

+5%

1,500

+3%

2,500

+2%

10,000

+1%

Rivera, 1999

Learning check 

A group of students want to know the age of the students in College of Engineering and Tecgnology but do not have the resources to survey the entire population of 2 500. if they want to use sample with 5% margin of error, what should their sample size be?

Learning check 

What should be the representative sample size if the population from which the sample will be taken is 15 000 and the desired margin of error is 10%?

Learning check 

At present Brgy. San Isidro has about 1 800 registered household members and the Brgy. Captain is planning to conduct a survey that would determine the members’ opinion on the issue of Solid Waste Dumping site in their barangay. How many respondents must be considered?

Ethical Issues

Ethical Issues 1. A permit to conduct the study must be properly sought from the authority. Willingness of the prospective respondent must also be considered. 2. The researcher must assure the respondents of confidentiality of the data that will be generated and used in the study. 3. The researcher must be willing to share the results or findings of the study with the institution where the respondents belong.

Ethical Issues 4. The researcher must maintain integrity in the publication of the findings of the study. 5. The researcher must not inflict any harm to the respondents especially during experimental research. 6. The researcher must consider the potential benefits that the respondents may get from the study. 7. The research must observe intellectual honesty in undertaking such research

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