This document discusses non-sampling error in surveys. It notes that non-sampling error occurs for reasons other than the sampling technique and can happen at every stage of a survey. There are two main types of non-sampling error: non-observation error, which includes non-coverage and non-response; and measurement error, which is when a respondent's answer differs from the true value. The document outlines various causes of non-sampling error and methods to reduce errors, such as improved training and monitoring of interviewers.

1. Non-Sampling ErrorNon-Sampling Error

2. Sampling and Non-Sampling ErrorSampling and Non-Sampling Error
 Sampling error arises due to the sampling
technique used to draw a sample.
Non-Sampling error is due to the reasons
other than sampling techniques during a
survey process.
Both the errors can be controlled but
cannot be made zero.
Complete enumeration is free from sampling
errors but is subject to non-sampling error.
Sample survey is subject to both sampling
and non-sampling error.

3. Non-Sampling ErrorNon-Sampling Error
 Sampling error decreases with increase in sample size, whereas non-
sampling error increases with increase in sample size.
 Non-sampling error is likely to be more in case of complete enumeration
survey than in case of a sample survey.
 Non-sampling error can occur at every stage of planning and execution of
a census or a survey. Such as:-
 Faulty definition
 Improper Training methodology
 Defective methods of data collection
 Incomplete coverage or non-response
 Improper or ambiguous questionnaire
 Lack of monitoring or supervision of primary staff
 Errors during tabulation
 Errors in data processing operations
 Improper interpretation during analysis and report writing

4. Non-Sampling ErrorNon-Sampling Error
Contd…Contd…
Major source of non-sampling error can
be divided into two groups.
1. Non-observation error
2. Measurement or observation error

5. Non-Observation ErrorNon-Observation Error
Non-Observation Error
Two sources of Non-observation error
are most important
1. Non-coverage
2. Non-response

6. Non-Observation ErrorNon-Observation Error
Contd…Contd…
 Non-coverage occurs when there are units in the population
of interest that have no chance of being sampled for survey.
 Possible reasons:
 Geographical limits like hilly areas, boundaries, etc.
 Institutional restrictions like military establishments, jails, etc.
 Incomplete frame differing from target population.
 Deliberate leaving of a portion of population out of frame,
Ex-A restriction to travel to a particular region due to riot
or civil unrest.
 Cost factor
 Use of out of date or inaccurate household listing as frame.

7. Non-Observation ErrorNon-Observation Error
Contd…Contd…
 Non-coverage arises due to errors or problems in
the frame being used for sample selection; but non-
response arises after frames have been constructed
and sample elements selected from the frame.
 Possible measures to control non-coverage error:
Reducing the level of non coverage through improved
field procedure like use of multiple frames or through
improving the listing process.
Clearly defining the target population.
Use of up to date more accurate household listing as
frame.

8. Non-Observation ErrorNon-Observation ErrorContd…Contd…
 Non-response occurs when a sampled unit fails to participate
in the survey, either completely or partially. Non-response is
believed to be more in household surveys.
 Non-response can be divided in two categories.
1. Unit non-response
2. Item non-response
 Unit Non-response
 Unit non-response can be at primary or secondary stage
sample units.
 Due to weather condition or natural disaster an entire 1st
stage unit may become non-response.
 A listed household may become non-responsive due to non-
cooperation of household member or the household
member may not be available.

9. Non-Observation ErrorNon-Observation Error
Contd…Contd…
 Unit Non-response
 Non-response of household unit may be due to following
reasons.
◦ Refusal to participation.
◦ Non-availability during survey period.
◦ Language barrier.
◦ Health condition, etc.
 Remedy
◦ Household member may be persuaded for giving reply.
◦ Frequent visit
◦ Awareness campaign for improving rate of participation.
◦ Increasing sample size to adjust non-response base upon the
past experience.

10. Non-Observation ErrorNon-Observation Error
Contd…Contd…
 Item Non-response
 Item response refer to the situation where some items of the
questionnaire are not answered by the respondent.
◦ Female health related questions.
◦ Questions related to disability.
◦ Questions related to income.
◦ Questions related to property, etc.
 Remedy
◦ Predicting missing values based on related trend analysis or from
other available information.
◦ Interviewers can be trained to get answer by cross questioning or
seeking for other related information from which the required
answer can be predicted.
◦ Interviewer may try to collect information in a range.

11. Measurement ErrorMeasurement Error
 Measurement error occurs when there is a difference
between the respondent’s answer to a question and
the true value.
 The measurement error is otherwise known as
observation error.
 Sources of Measurement error
 Effect of questionnaire design
 the topic it covers
 wording of the questions
 Length of the questions
 Length of the questionnaire
 Order of the questions

12. Measurement ErrorMeasurement Error
Contd….Contd….
Sources of Measurement error
 Mode of data collection
 Face to face interview: Use electronic mode like Tabs/
Palmtops improves quality of data collection and
reduces error than paper and pencil.
 Presence of outside members may affect the answers
 Direct Observation
 Interviewer effect
 Interviewer error can be reduced through interviewer
training, supervision and workload manipulation.
 Respondent effect

13. Measurement ErrorMeasurement Error
Contd….Contd….
Effective Training can reduce Non-
sampling error
 There should be less layers of training
 Uniform module should be developed so
that every trainer and every trainee should
talk the same language.
 Manual or module should have empirical
examples or filled in schedules.
 FAQ and common mistakes committed
should be part of training manual.

14. Measurement ErrorMeasurement Error
Contd….Contd….
Effective monitoring mechanism can
reduce Non-sampling error
 Sample selection for supervision should be
done at central level.
 Higher layer of supervision should be done
from among the units already checked at
lower level.
 Supervision should be minimum two levels.
 Technical supervision should be done on
some key indicators.

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