The Stage 6 Science (Physics, Chemistry and Biology) syllabus asks students to distinguish between these terms in both first-hand investigations and when using secondary sources.
Students often confuse these terms – do you know the difference?
For Secondary Sources (journals, articles, websites, text, prior experiments)
Often students are asked to “Identify data sources, gather, process, analyse and present information from secondary sources”. When researching information, using articles from journals, mass media, textbooks etc, it is important to identify your sources in the correct manner and the information must be accurate.
To ensure secondary sources are accurate, the information from the site or source must be both valid and reliable.
To determine if the information you are gathering is valid, you must consider or evaluate the following:
• whether the information relates to the problem or hypothesis being investigated.
To determine if the information you are gathering is reliable, you must consider or evaluate the following:
• the author of the article’s credentials (i.e. the author is qualified in this area). For example, was the author a teacher, a scientist in that field etc?
• whether the purpose of the article is not resulting in bias
• whether the site or publication is reputable, i.e. .gov.edu, biology textbook
• whether the data was gathered using an appropriate method and measuring devices
• whether it is current (check date) This means that if your information is current, written by an expert in the area you are investigating, without bias and is in a reputable publication, then your information could be considered reliable.
To determine if the information you are gathering is accurate, you must consider or evaluate the following:
• whether the information can be substantiated in more than one reliable source. (i.e. is the information consistent with information from other reputable sources?).
This means that if you can find similar information in at least two valid and reliable sources, then your information could be considered accurate.
First Hand Investigations (Your experiments)
Students planning a first-hand investigation must consider issues related to accuracy, reliability and validity.
These will impact on the choice of equipment and how confident they are about the conclusions drawn from the results of the investigation.
A valid experiment is a fair test. A method is valid if:
• it investigates what you think it will investigate (i.e. the procedure actually tests the hypothesis and the experiment includes an appropriate range of values).
• it incorporates suitable equipment (e.g. measuring cylinder to measure volume rather than a beaker)
• variables are controlled
• appropriate measuring procedures are included
Discussions about validity must:
• identify what validity is
• identify the factors that affect the validity of the particular experiment you are considering (the variables that must be controlled, the appropriate equipment, the range of values etc)
• assess the overall validity of the experiment
A reliable experiment has results which can be obtained consistently. To ensure that results are reliable:
• the experiment must be repeated and consistent results obtained (within an acceptable margin of error)
Note: Repetition will only determine reliability (it will NOT improve it).
A useful analogy is that of a friend arriving on time for appointments. If they arrive on time once, you can’t say they are reliable or not, but if they arrive late over and over again, then you can say they are unreliable. Just because you make repeat observations of them arriving doesn’t make them reliable.
“The relationship between reliability and validity can be confusing. Measurements and other observations can be reliable without being valid. A faulty measuring device can consistently provide a wrong value therefore providing reliably incorrect results. However, measurements and observations cannot be valid unless they are reliable and accurate.” (Curriculum Support 2006 Vol. 11 No. 2)
Discussions about reliability must:
• identify what reliability is
• identify that reliability is assessed by repeating the experiment and averaging the results
• identify that repetition minimises the effect of random errors/outliers and/or allows them to be removed or disregarded
• give examples of possible random errors that may have crept into the experiment you are considering
• assess the overall reliability of the experiment
Accuracy depends on the design of the experiment (i.e. the validity of the method) and the sensitivity of the instruments used. Results are accurate if:
• they are close to the true value of the quantity being measured
• they can be substantiated in secondary sources
• Note: Accuracy is important by making the experiment as valid and reliable as possible.
Accuracy and repetition: The experiment should be repeated at least twice (i.e. carried out three times) and the results averaged. This ensures that the effect of random errors is minimised or that the outliers can be disregarded or removed. Random errors are errors that might affect your experiment the first time you do it, but not the second or third, for example. Random errors may also be present in every measurement taken and be caused by unpredictable fluctuations in the readings of a measurement apparatus, or in the experimenter's interpretation of the instrumental reading. In any experiment that involves measuring a variable that exhibits natural variation (particularly biological variables or environmental factors), the accuracy of the results will be improved by repetition. In statistical terms, the mean of the sample will more closely reflect the population mean. Similarly, investigations that involve measuring the probability of an event occurring are also improved with repetition. For example, one of the reasons why Gregor Mendel got such accurate results was because he tested large numbers of plants. This is essentially “the law of large numbers”: the average of the results obtained from a large number of trials should be close to the expected value, and will tend to become closer as more trials are performed.