Sources of error in lab experiments and laboratory tests


One of the major research aspects of laboratory science is physical and chemical testing; and its test findings are the primary scientific basis for assessing product quality. Physical and chemical laboratory experiments include three primary sources of error: systematic error, random error and human error. These sources of errors in lab should be studied well before any further action.

So, what are the particular sources of each error?

The reliability of physical and chemical testing has been significantly impaired; by equipment, samples, instruments, lab environment, reagents, operating procedures and other factors; leading to many errors in physical and chemical testing.

System Error in laboratory experiments

Systematic error applies to repeated measuring of the same object under repeated conditions of measurement. The amount of the error value is either positive or negative; which is called the fixed system error in laboratory experiments and laboratory tests. Or the error changes show a certain law; which is also called the variable system error, as the measurement conditions varies.

The systemic sources of error is caused primarily by:

  • The incorrect method of measurement in laboratory experiments
  • The incorrect method of using the instrument in laboratory experiments
  • The failure of the measuring instrument in laboratory experiments
  • The performance of the testing tool itself in laboratory experiments
  • The inappropriate use of the standard material and the changing environmental conditions in laboratory experiments

With certain steps and proper Laboratory Equipment these sources of errors can be minimized and corrected.

Different types of system errors are:

Method error in laboratory experiments

The method error in laboratory experiments refers to the error created by the very process of physical and chemical examination. This error is inevitable so often the test result is low or high.

For example, the dissolution of the precipitate is likely to trigger errors while conducting gravimetric analysis in physical and chemical tests; there is no full reaction during the titration, or a side reaction occurs due to the incoherence of the end point of the titration with the metering level.

Instrument error in laboratory experiments

The instrument error in test labs is caused primarily by laboratory instrument inaccuracy. If the meter dial or the zero point is inaccurate, for instance; the measurement result would be too small or too big. Unless the adjustment is not done for too long, the weighing error will eventually occur. The glass gauge has not undergone standard and scale testing; so it is used after purchasing from the manufacturer, which will allow the instrument error to occur.

Reagent error in laboratory experiments

The reagent error in lab test is caused primarily by the impure reagent or the inability to meet the experimental provisions; such as the existence of impurities in the reagent used in the physical and chemical testing phase; or the existence of contaminated water or reagent contamination that may influence the results of the examination; or the storage or operating climate. Changes in reagents and the like can cause errors in reactants.


Random Error in laboratory experiments

Error caused by various unknown factors is known as random error. This error poses erratic changes at random, primarily due to a variety of small, independent, and accidental factors. The random error is atypical from the surface. Since it is accidental, the random error is often called unmeasurable error or accidental error.

Statistical analysis can also measure random sources of error in lab, unlike systemic errors; and it can also determine the effect of random errors on the quantity or physical law under investigation. To solve random errors, scientists employ replication. Replication repeats several times a measurement, and takes the average.

Although, it should be noted that in the usual physical and chemical testing phase, which has some inevitability, both the systematic error and the random error do exist. The disparity in results caused by the inspection process mistake of the usual physical and chemical inspection personnel, incorrect addition of reagents, inaccurate procedure or reading, mistake in measurement, etc., should be considered “error” and not an error.

Thus, if there is a significant difference between repeated measurements of the same measuring object; whether it is caused by “error” should be considered. in such situation, the source of error in lab should be examined carefully, and its characteristics should be calculated.

An Example of some random sources of errors in lab

Example for distinguishing between systemic and random errors is; assuming you are using a stop watch to calculate the time needed for ten pendulum oscillations. One cause of error in starting and stopping the watch is your reaction time. You may start soon and stop late during one measurement; you can reverse those errors on the next.

These are accidental errors, since all cases are equally probable. Repeated tests yield a sequence of times, all slightly different. In random they differ around an average value. For example, if there is also a systemic mistake, your stop watch doesn’t start from zero; so the calculations will differ, not about the average value, but about the displaced value.

In this example both random and systemic source of errors in lab explained.


Human Error in laboratory experiments

The human error in laboratory experiments and lab tests primarily refers to the mistake in physical and chemical inspection phase caused by the factors of the inspector; particularly in the following three aspects:

Operational error in laboratory experiments

Operational error applies to the subjective factors in regular activity of the physical and chemical inspectors. For instance, the sensitivity of the inspector to observing the color would result in errors; or there is no effective protection when weighing the sample, so that the sample is hygroscopic.

When washing the precipitate, there is an error in the absence of appropriate washing or extreme washing; Throughout the burning precipitation, did not regulate temperature; Unless the burette is not rinsed in the physical and chemical testing process before the liquid leakage, the liquid hanging phenomenon will occur which will allow the air bubbles to linger at the bottom of the burette after the liquid is injected; Inspectors looking up (or down) the scale at the time of the degree would cause errors.

Subjective error in laboratory experiments

Subjective errors are caused mainly by the subjective considerations of physical and chemical test analysts. For example, because of the difference in the degree of sharpness of color perception, some analysts believe the color is dark when the color of the titration end point is discriminated against, but some analysts think the color is brighter;

Because the angles from which the scale values are read are different, some analysts feel high while some analysts feel low in situations. Moreover, many observers would have a “pre-entry” tendency in the actual physical and chemical inspection job, that is, subjectively unconsciously biased towards the first measurement value whenever reading the second measurement value.

Negligible error in laboratory experiments

Negligible error refers to the mistake caused during the physical and chemical examination by the inspector’s reading mistake, operation error, measurement error etc. A individual can, for example, record an incorrect value, misread a scale, forget a digit while reading a scale, or record a calculation, or make a similar blunder.

Errors can lead to incorrect results, and knowing the sources of error in lab will help us mitigate error occurrence and increase test results quality.


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