Non sampling error

How to Minimize NON SAMPLE ERROR:;

1. MRINMOY PRATIM BHARADWAZ M.Sc BIOSTATISTICS & DEMOGRAPHY IIPS-MUMBAI 2015-17 BATCH 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 L ack 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) F aulty definition(Mistake) D efective 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….