non sampling error

Non-Sampling ErrorNon-Sampling Error

Sampling and Non-Sampling Sampling and Non-Sampling ErrorError

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.

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

Non-Sampling ErrorNon-Sampling ErrorContd…Contd…

Major source of non-sampling error can be divided into two groups.

1. Non-observation error 2. Measurement or observation

error

Non-Observation ErrorNon-Observation ErrorNon-Observation Error Two sources of Non-observation

error are most important 1. Non-coverage 2. Non-response

Non-Observation ErrorNon-Observation ErrorContd…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Cost factor Use of out of date or inaccurate household listing as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.


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.


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-response2. 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.


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.


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.

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

Measurement ErrorMeasurement ErrorContd….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


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.


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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