How to Minimize NON SAMPLE ERROR:;

1. M R I N M O Y P R A T I M B H A R A D W A Z
M . S C B I O S T A T I S T I C S & D E M O G R A P H Y
I I P S - M U M B A I
2 0 1 5 - 1 7 B A T C H
NON-SAMPLING ERROR

2. WHAT IS NON-SAMPLING ERROR
 It is a general assumption in the sampling theory
that the true value of each unit in the population can
be obtained and tabulated without any errors. In
practice, this assumption may be violated due to
several reasons and practical constraints. This
results in errors in the observations as well as in the
tabulation .Such errors which are due to the factors
other than sampling are called non-sampling
errors.

3. CATEGORIES
Non-sampling errors may be broadly classified into
three categories---
Specification errors(planning stage)
 Coverage error
 Content error
Ascertainment errors(field stage)
Tabulation errors(analysis stage)

4. SOURCES OF NON-SAMPLING ERRORS
Non sampling errors can occur at every stage of planning and execution of
survey or census. It occurs at planning stage, field work stage as well as at
tabulation and computation stage. The main sources of the non-sampling
errors are
 Lack of proper specification of the domain of study and scope of
investigation,
 Incomplete coverage of the population or sample(inability to
respond/Refusal to respond/inability to contact)
 Faulty definition(Mistake)
 Defective methods of data collection and Tabulation
errors(Researcher effect).

5. Reasons
 The data specification may be inadequate and inconsistent
with the objectives of the survey or census.
 Due to imprecise definition of the boundaries of area units,
incomplete or wrong identification of N units, faulty
methods of enumeration etc, the data may be duplicated or
may be omitted.
 The methods of interview and observation collection may
be inaccurate or inappropriate.
 The questionnaire, definitions and instructions may be
ambiguous.

6.  The investigators may be inexperienced or not trained
properly.
 The recall errors may pose difficulty in reporting the true
data.
 The scrutiny of data is not adequate.
 The coding, tabulation etc. of the data may be erroneous.
 There can be errors in presenting and printing the
tabulated results, graphs etc.
 In a sample survey, the non-sampling errors arise due to
defective frames and faulty selection of sampling units.
CONTINUE….

7. SOME MEASURES TO TAKE CARE OF NON-
SAMPLING ERRORS
 To reduce response errors, telephonic interview can be
done instead of mail or face to face interview.
 To reduce the errors due to the difference between
frame and target , we should use the most recently
updated list of respondents or map of the area under
study.
 To reduce the errors due to investigators negligence ,
we should appoint well experienced as well as well
educated personnel to supervise.
 The workers should be well paid so that they have some
interest to work with honesty.

8.  Investigators should be local , so that he can
communicate in local languages. We can crosscheck the
data collected by the investigators through different
questions and with the data available from some other
sources.
 Application of quality design principles in preparation
of instrument and instructions.
 Extensive data-cleaning procedure to detect and correct
mistakes including validity and reliability checking.
 Using external data sources to detect and correct errors
once identified.
CONTINUE….