Data collection is a science, not an art form. Be sure to use rigor and thought before assembling the data that you seek to analyze.

Ensuring Data Accuracy & Integrity

Be sure to address these point in your data collection plan. and make use of a data collection form.

  • Data should not be removed from a set without an appropriate statistical test or logic.
  • Generally, data should be recorded in time sequence.
  • Unnecessary rounding should be avoided.
    • If done, should be late in the process.
  • Screen the data to remove entry errors.
  • Avoid emotional bias.
  • Record measurements of items that change over time as quickly as possible after manufacture and again after the stabilization period.
  • Each important classification identification should be recorded alongside the data. (Ex. Time, machine, operator, gage, lab, material, conditions, etc).
  • Also see data sampling.

Coding Data

Sometimes it is more efficient to code data by adding, subtracting, multiplying or dividing by a factor.

Types of Data Coding

  • Substitution – ex. Replace 1/8ths of an inch with + / 1 deviations from center in integers.
  • Truncation– Ex. data set of 0.5541, 0.5542, 0.5547 – you might just remove the 0.554 portions.

Problems due to NOT Coding

  • practitioner tries to squeeze too many #s on a form – poor usability & legibility.
  • increased errors in data entry.
  • insensitivity of analytics due to rounding

Effects of Coding Data

  • Will affect the mean to the extent that the mean must be uncoded for reporting purposes.
  • Coding and uncoding of the mean will be exactly opposite. (Ex. Add X, subtract X or multiply by X, divide by X.)
  • The effect the coding has on standard deviation depends on how the data is coded.

Rounding Data

  • Rounding data will affect the standard deviation but not the mean – if done properly.

Also See:

Data Sampling

Data Collection Form

Data Collection Plan

Data Collection Reading List

Quality Control and Industrial Statistics. Fifth Edition A very good and comprehensive reviews of Acceptance Sampling, Control Chart and Statistics.

ASQ Six Sigma Black Belt Exam Data Collection Questions

Question: An important aspect of data collection is that the data collector should

(A) determine the dispersion of the data
(B) know how the data are to be used
(C) use a control chart to analyze the data
(D) use a stratified sampling plan

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Question: A method that changes data without significantly reducing accuracy or precision is known as

(A) bias adjustment
(B) statistical efficiency
(C) blocking
(D) coding

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ASQ Six Sigma Green Belt Exam Data Collection Questions

Question: When the sampling method used creates a difference between the result obtained from the sample and the actual population value, the difference is known as

(A) correlation
(B) precision
(C) accuracy
(D) bias

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