Bookmark this page. Poll Which percentage of your results is within 1cm of the mean? MENU 1: Home. Print Friendly Page Recommended by:. Validity Validity describes whether the results of an experiment really do measure the concept being tested. Accuracy Accuracy describes how well a measuring instrument determines the variable it is measuring. It can be employed in two ways An accurate measuring instrument, say a thermometer, is one whose readings confirm a known result.
The level of accuracy of a measuring instrument determines the detail to which it can measure. Always put repetition if if asks for something like "How could you improve the reliability of this experiment? Accuracy is like parallax error and using the same equipment because timers are different and rulers are different I hope this helped :S I never really understood the meanings of these either and so I kind of made it up and for now it has proven me fine.
Most probably look it up in the textbook? Aluminesis Member. Damn, my teacher gave us a sheet of definitions for these but I chucked all my HSC sheets out a few days back.
I never completely understood them myself, but the general consensus from all my classes was: Validity: the experiment correctly tests the aim - i. If in biology, for example, you were testing say the level of enzyme activity with respect to changes in temperature, you obviously wouldn't do one experiment at 30 degrees and say ph 4 and another at 40 degrees at pH 8; you'd keep everything except temperature constant.
Reliability: how consistent the results are. When you repeat an experiment and get the same results, it is reliable. Accuracy: the easiest one, simply how accurate it is. Measuring with a stopwatch that calculates milliseconds is obviously more accurate than one that only calculates up to seconds.
A data logger is obviously more accurate than the naked eye. A funny example my teacher told us was this: a scientist set out to prove that cockroaches listened through their legs. He ripped of a cockroach's legs, set it on a table and clapped loudly over it.
It didn't move. He did it again; ripped off the legs, clapped, and it didn't move. Again, not completely sure that my definitions are right. Reliability and accuracy I'm fairly confident about; validity was the one I was always iffy with. I suggest checking with a couple of teachers and classmates to be on the safe side.
In school assessments, it'd be safest to go by what your teacher tells you. The measurements are usually analysed in an experimental report, which is set out in a clear format to help the reader understand different aspects of the experiment, like the aim, the equipment and method used, the results obtained, how they were analysed, and what conclusions can be drawn.
When writing the method of an experiment, you must ensure that each step of the method incorporates reliability, accuracy or validity. Validity relates to the experimental method and how appropriate it is in addressing the aim of the experiment:. Several aspects of the experiment can contribute to validity: the equipment, the experimental method, and the analysis of the results. Although it may seem obvious, the appropriate equipment needs to be used.
The equipment must be suitable for carrying out the experiment and taking the necessary measurements. The experiment is ultimately testing a relationship between cause and effect: how changing X affects Y. To address this, you must only change X, and see what happens to Y.
If you allow other changes at the same time, then you cannot make a valid conclusion about how X affected Y, since Y may have been affected by the other changes as well. The correct way to describe this is in terms of the independent, dependent, and control variables. The independent variable in an experiment is the one you set X. The dependent variable is the one you measure Y, because it depends on X. All other variables are called control variables, and they must be kept constant to prevent them from affecting the dependent variable.
This forms part of the experimental method. The method including the analysis may contain some assumptions that need to be satisfied, e. The experimental method must ensure that all the assumptions are satisfied, otherwise, you will end up using a method or analysis that is inappropriate, and the result will be invalid.
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