Random vs. Systematic Errors – Know the Difference

24.11.22 Reliability & Validity Time to read: 6min

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In scientific research, you will often encounter random vs. systematic errors. Random vs. systematic errors are known as measurement errors, which make the difference between the observed and true values of something. This post discusses random vs. systematic errors.

Random vs. Systematic Errors – In a Nutshell

Below are some takeaways on random vs. systematic errors:

  • Measurement errors are differences between observed and true scores of something.
  • Random errors are unpredictable and can deviate from the true score in either direction.
  • Systematic errors are consistent differences, and they skew the observations in a specific direction.

Definition: Random vs. systematic errors

In random vs. systematic errors, the former (random) is a chance difference between observed and true values. By chance, it means that they are not intended. For instance, a random error may result from a researcher misreading the weighing scale.

In random vs. systematic errors, the latter (systematic) is a consistent difference between observed and true values. This error is usually consistent. For example, a systematic error occurs when a miscalibrated scale may register inaccurate weights.1

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Random vs. systematic errors

When comparing random vs. systematic errors, the latter is considered worse. In scientific research, random errors are not considered a mistake but a result of unavoidable variability in measurement. For instance, if you measure the same thing severally, you may get different results due to environmental factors and inaccurate instruments. However, measurement variability can affect your ability to conclude the relationships between the variables. Unfortunately, this issue is more common with systematic errors.

Let’s look at other differentiating elements of random vs. systematic errors.

Precision vs. accuracy: Random vs. systematic errors

Random errors primarily affect precision. Note that precision is how reproducible the same value is under equivalent conditions. In contrast, systematic errors affect accuracy, which is how close observed measurements are to the factual values.

For high precision, you need to get repeated observations as close to each other as possible. In contrast, for accuracy, you need to get the measurements in your observation as close to the targeted value (true) as possible.

Random errors introduce inconsistency between diverse measurements of the same things, while systematic errors tilt your measurements from the true value in a definite course.

For example, if you measure the same thing repeatedly, your measurements will vary around the true value when you only have a random error. Therefore, random errors are not so problematic, especially in studies with large samples.

In contrast, systematic errors are more of a problem because they can tilt your data, resulting in false or inaccurate conclusions. Eventually, you may obtain a false negative or positive deduction of the correlation between variables in your study.2

Random vs. systematic errors vs. no error

Random error: Random vs. systematic errors

The impact of random error in your measurements is usually unpredictable. For example, the measurements may be higher or lower than the true score.

Random error is also known as noise because it blurs the factual score (true value) of what you want to measure.

How does a random error occur?

Random may occur from many sources, including:

  • Natural disparities in the real-life or experimental context
  • Using faulty instruments
  • Differences between the participants or units in the study
  • Poorly conditioned trial processes


Source of random error Example
Natural contextual variations In a trial, participants take memory tests at different times of the day where some perform better at specific times will not produce authentic results for all.
Unreliable instruments You use a tape measure to collect data. Rounding up the data to the nearest centimeter will cause a random error.
Individual differences In a trial where you measure pain response, you may get a random error because some participants have a higher pain tolerance than others.
Poor experiment conditions Testing pain resistance in a cold room may not give you the most precise measurements because the temperature affects the amount of pain.

Decreasing random error: Random vs. systematic errors

Random vs. systematic errors are always present in research. While you cannot eradicate random error 100%, the following methods can decrease it.

Measure multiple times

You can take the measurements repeatedly and then use their average as the observation value. Doing this will bring you closer to the factual score.

Using a larger sample

Increasing the sample size also helps reduce random errors because they cancel each other in different directions. Therefore, a larger sample will increase precision.

Control the variables

Conducting controlled experiments can also eliminate extraneous variables that cause random errors. However, controlled conditions must be present for all participants.

Systematic error

In random vs. systematic errors, the latter means that your measurements of the same thing will vary predictably. Therefore, every observed value will vary from the true score in the same course. For instance, they may all be less than the true value or more. In some cases, the variations may also feature the same amount.

Systematic error is also known as a bias because the values are skewed consistently, hiding the true score. Therefore, it may cause inaccurate deductions.

Two types of systematic errors

A difference between random vs. systematic errors is that systematic errors come in two quantifiable types. They are:

1. Offset/additive/zero-setting error:

  • This occurs when the measurement scare is not calibrated to a correct zero point.


When measuring participants’ weights in a study, you may misread the “1” value as the zero point. Therefore, all measurements will have an extra centimeter to them.

2. Scale factor/correlational systematic/multiplier error:

  • This is when the values consistently differ from the factual score proportionally (like by 10%)


In an experiment measuring the weight of newborns, the weighting scale may add 10% to each weight. Therefore, if the recorded value is 11kg, the true weight is 10kgs.

How does a systematic error occur?

Various things may cause systematic errors in research, like materials and data collection procedures. However, the most common (but not all) are:

  • Response bias
    • This occurs when your data collection materials promote inauthentic answers from participants. For example: using leading questions in a questionnaire can trigger inauthentic responses.
  • Experimental drift
    • Occurs when observers become bored, unmotivated, or tired after long data collection. For example: after long hours of collecting data, coders may deviate from standardized procedures.
  • Sampling bias
    • Occurs when some participants have a higher chance of being part of a study than others.3

Decreasing systematic error

The methods below can help you reduce systematic errors.


You use multiple techniques to record annotations instead of one instrument or method. For example, you can use a ruler and a string to measure participants’ wrist circumference instead of a tape measure only.

Regular calibration

Regular instrument calibration can help you maintain accuracy. However, it would help if you had an accurate reference to ensure proper calibration. You can also calibrate the observers or researchers by providing a standardized procedure for data recording and conducting routine checks.


Random sampling can help prevent sample bias, a source of systematic errors. Additionally, using the random assignment technique to place participants in various treatment conditions can help.


Finally, you can hide the condition assignment from participants and researchers to get authentic observations without influence from experimenter expectancies and environmental demand characteristics.4

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Random error is a coincidental difference between observed and factual values, while, systematic errors are proportional or constant differences between factual and observed values.

In random vs. systematic errors, systematic ones are worse than random errors. This is because random errors are usually a natural part of the measurement and have variability, while systematic ones may easily go undetected.

Random vs. systematic errors are both measurement errors. A measurement error is a difference between the values you observe during an experiment and the factual ones.

Yes, you can reduce the impact of random vs. systematic errors in scientific research by recognizing their source. Identifying whether they are random vs. systematic errors also helps because random vs. systematic errors have different reduction methods.


1 Yadav, Piyush. “Difference between Systematic and Random Error.” Accessed November 10, 2022. https://askanydifference.com/difference-between-systematic-and-random-error/

2 Dunee. “Difference Between Random Error and Systematic Error.” March 21, 2012. https://www.differencebetween.com/difference-between-random-error-and-vs-systematic-error/

3 Helmenstine, Anne Marie, Ph.D. “Random Error vs. Systematic Error.” ThoughtCo. Accessed November 10, 2022. https://www.thoughtco.com/random-vs-systematic-error-4175358 

4 WallStreetMojo. “Random vs Systematic Error.” Accessed November 10, 2022. https://www.wallstreetmojo.com/random-vs-systematic-error/