Microsoft Word research method fm doc

Random sampling strategies to collect quantitative data: 
If the aim of a study is to 
measure
variables distributed in a population (e.g., diseases) or to test hypotheses about 
which factors are contributing significantly to a certain problem, we have to be sure that we 
can generalise the findings obtained from a sample to the total study population. Then, 
purposeful sampling methods are inadequate, and probability or random sampling methods 
have to be used. 
b) Probability sampling methods:
They involve random selection procedures to ensure 
that each unit of the sample is chosen on the basis of chance. All units of the study 
population should have an equal or at least a known chance of being included in the 
sample. 
1. Simple Random Sampling (SRS):
This is the most basic scheme of random 
sampling. To select a simple random sample you need to: 
ƒ
Make a numbered list of all the units in the population from which you 
want to draw a sample. Each unit on the list should be numbered in 
sequence from 1 to N (Where N is the Size of the population). 
ƒ
Decide on the size of the sample 
ƒ
Select the required number of sampling units, using a “lottery” method 
or a table of random numbers. 
2. Systematic Sampling:
Individuals are chosen at regular intervals (for example, 
every 5
th
, 10
th
, etc.) from the sampling frame. Ideally we randomly select a number 
to tell us where to start selecting individuals from the list. For example, a 
systematic sample is to be selected from 1000 students of a school. The sample 
size is decided to be 100. The sampling fraction is: 100/1000 = 1/10. The number 
of the first student to be included in the sample is chosen randomly by picking one 
out of the first ten pieces of paper, numbered 1 to 10. If number 5 is picked, every 
tenth student will be included in the sample, starting with student number 5, until 
100 students are selected. Students with the following numbers will be included in 
the sample: 5,15, 25, 35,45, . . . , 985, 995.

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Research methodology 
43
ƒ
Systematic Sampling is usually less time consuming and easier to 
perform than SRS. 
ƒ
It provides a good approximation to SRS. 
ƒ
Should not be used if there is any sort of cyclic pattern in the ordering 
of the subjects on the list. 
ƒ
Unlike SRS, systematic sampling can be conducted without a sampling 
frame (useful in some situations where a sampling frame is not readily 
available). 
4. Stratified sampling: If it is important that the sample includes representative 
groups of study units with specific characteristics (for example, residents from 
urban and rural areas), then the sampling frame must be divided into groups, or 
strata, according to these characteristics. Random or systematic samples of a 
predetermined size will then have to be obtained from each group (stratum). 
This is called stratified sampling.