Reducing Mail Survey Errors

Mail surveys are the preferred survey methods due to their low cost and ease of implementation. However, like other survey methods, they are also prone to various errors such as sampling error, non-coverage error, non-response error, and measurement error. This blog intends to put forward ways to minimize the impact of these errors on the survey results.

Sampling Error

The most common error is the sampling error which exists because the sample selected to conduct the survey might not be the right representative of the population.

Using statistics, it can be showed that for a given confidence level, increasing the sample size can reduce the sampling error. This is true for random or probabilistic sampling methods. How large should be the sample size depends on the trade-off between precision of estimation and costs.

Non probabilistic sampling involves subjective selection of sample. Therefore, precise estimate of sampling error in such cases is not statistically feasible.

Coverage Error

Under-coverage and over-coverage, both can affect the results of the mail survey conducted. Coverage error affects the survey estimates if the characteristics of the respondents covered or not covered in the survey, differ from the characteristics of those covered. Having complete, up-to-date sample frame can reduce the chance of incorporating coverage error.

Non-Response Error

Non-response error arises when some of the sample members do not respond to the survey questions. A lot of research has been conducted to improve the response rates. Some of the variables which have been found to have positive effect on response rate are the number of contacts (more the better), relevance/ salience of the questionnaire topic, government sponsorship (compared to private sponsorship), specificity of the target sample (compared to general population), incentives, pre-notifocation, stamped return postage, etc.

Research on incentives has shown that response rates increase only when incentives are provided with initial mail and not for those where the incentives were made contingent on return response. Further, no statistically significant difference was found between monetary and non-monetary incentives.

Research also has shown that that through mixed-mode surveys which use mailing questionnaires, electronic mail, telephone, and face-to-face interviews, all in some proportion, can increase the response rate compared to a typical mail survey.

Measurement Error

Measurement errors arise from the respondents’ side when they either do not respond to certain questions, or leave open-ended questions unanswered/incomplete, or fail to follow instructions. Measurement errors signify the difference between the recorded answers and the true answers.

Mail surveys have some advantage when it comes to measurement errors due to absence of an interviewer which not only lessens the likelihood of driving the respondents’ to provide socially desirable responses and but also removes interviewers’ bias.

Some ways to reduce measurement errors are:

  • Pre-testing the questionnaire
  • Making the questionnaire more respondents’ friendly
  • Making questionnaire instructions clear and simple
  • Streamlining the questionnaire design in case of mixed-mode surveys to reduce deviance among the different modes


Section A _Group 3_Sameer Pandey_13PGP047


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