Sample Size• The number of sampling units selected from the

population for investigation.

• The size of the sample should be neither to big nor

too small. It should be optimum.

Factors affecting sample size

• Homogeneity or Heterogeneity of the population.

• Nature of study

• Practical consideration

• Standard of accuracy

• Type of sampling

• Size of questionnaire

Sampling Errors

• The errors which arise due to use of sampling

surveys are known as the sampling errors.

Types of Sampling Errors

• (a) Biased Errors

• (b) Un biased Errors

Biased Errors• Biased errors are those errors which arise as a result of

any bias or prejudice of the person in selecting a

particular sampling method.

• Known as- cumulative errors, non compensating

errors, because bias or prejudice forms a constant of

errors that does not decrease in a large population as

the number in the sample increases.

Causes for bias• Faulty process of selection ;

• The investigators desire or motive to obtain a certain result

from the sample survey may influence his selection of the

samples, consciously or unconsciously.

• Failure to cover the whole samples.

• An appeal to the vanity of the person interacted may give

rise to yet another kind of bias.

• Bias due to faulty collection of data

• Negligence or prejudice of the person collecting

information either in asking the questions or in

recording the answers.

• Poorly designed questionnaire.

• Un organized collection procedure, faulty editing

or coding of response.

Bias in analysis

• Faulty methods of analysis of data may also

introduce bias.

Avoidance of bias• Draw samples either at random or at random subject

to such restrictions as, while improving the accuracy,

would not introduce bias into the result.

• The survey once selected should be strictly adhered

to throughout the enquiry.

• Investigator should try to investigate the entire

sample.

Un Biased Errors• They are such errors which are either accidental or

arise in the natural course of events and are without

any bias or prejudice.

• Known as – Random sampling errors,

• Because if a census is taken such errors could be

expected to disappear.

Methods of reducing Sampling Errors • Removing the errors of bias

• Enlarging the size of the sample.

• The sampling error is approximately inversely

proportional to the square root of the number of

units included in the sample.

Relationship between Sampling Error and Sample Size

Sampling Errors

Sample Size

Non Sampling Errors• Non sampling errors are errors which arise from

sources other than sampling.

• Errors arises due to :

• (a) un interview able

• (b) not found

• (c) not at homes

• (d) refuses

References• Research methodology – Pankaj Madan

• Research Methodology in Social Science

– Chava Nachmias

• Research Methodology and Statistical Techniques -

Santhosh Guptha

• Research Methodology in Social Science –

Devendra Thakur