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Difference Between Accuracy, Validity, Reliability and Precision

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    In regards to scientific investigations, could somebody please clarify for me what these words mean? I'm getting them all confused.
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    To get the ball rolling the difference between Accuray and Precision.

    Precision is to with the instruments that you use. A thermometer can be in degrees centergrade or in 0.1 degrees. The latter is more precise.

    Whereas accuracy is how close your value is to the real value.

    Is that is any help?
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    (Original post by IPlayThePiccolo)
    In regards to scientific investigations, could somebody please clarify for me what these words mean? I'm getting them all confused.
    I remember Revd Mike posted a useful picture explaining accuracy and precision. Reliability is difficult for me to explain without using the word reliable, but I'm sure it's when a number of scientists do the same experiment and get the same results, that result is said to be reliable.

    Definitions are on this page http://store.aqa.org.uk/qual/gce/pdf...-TRB-OGHSW.PDF
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    Well, regarding accuracy vs precision:

    http://labspace.open.ac.uk/mod/resou....php?id=346092

    Reliability can be described as the likeliness of someone repeating the experiment and getting the same result.

    I'd guess validity is to do with how 'properly' the experiment was performed, and whether it was 'proper' enouh for the conclusion to be made.
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    Validity- was the investigation taken out on the correct assumptions and were results logically drawn
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    Another way to look at it....

    An experiment where you can faithfully tell the difference between a change of 0.00001% and 0.00002% would be precise. (Problem: more decimal points doesn't mean an actual biological difference in all settings!)

    An experiment where you can repeat it many times and get all results close to one another is very reliable. (Problem: it could be the same wrong result each time!)

    An experiment where you can actually demonstrate by other means that it's representative of a 'true' value is accurate. (Problem: How do you determine the true value?)

    Validity is just whether your experiment has sufficient integrity to be asking the right questions. A very very good study of a single beach wouldn't give you valid predictive ability against another beach: only a study of several beaches would work towards that.
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    (Original post by IPlayThePiccolo)
    In regards to scientific investigations, could somebody please clarify for me what these words mean? I'm getting them all confused.
    Accuracy: A measure of how close the data is to the actual true value. Not the difference between accuracy precision. If a man is 1.81m tall, a measurement of 1.743 is precise but not accurate.

    Precision: The closeness of repeated measurements to one another. Precision involves choosing the right apparatus and using it properly. Precise readings are not necessarily accurate. A faulty piece of equipment or incorrectly used apparatus may give preide readings (all repeated values are close together) but inaccurate (not true) results. Eg in an experiment with a colorimeter, using a dirty of scratched cuvette (sample tube) might give precise readings but they will be highly inaccurate.

    Reliability: If a measurement or test is reliable, it gives consistent results each time the activity is repeated. When undertaking an investigating a large number of repeats should ideally be taken, and any readings that vary considerably from the others (anomalous) should be repeated.

    Validity: The confidence that researchers put in a set of results and the conclusions drawn from those results. Results are valid if they measure what they are supposed to, and if they are precise, accurate and reliable.

    Source:Collins Student Support Materials AQA AS BIO Unit 2 book
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    (Original post by namzy01)

    Precision: The closeness of repeated measurements to one another. Precision involves choosing the right apparatus and using it properly. Precise readings are not necessarily accurate. A faulty piece of equipment or incorrectly used apparatus may give preide readings (all repeated values are close together) but inaccurate (not true) results. Eg in an experiment with a colorimeter, using a dirty of scratched cuvette (sample tube) might give precise readings but they will be highly inaccurate.

    Reliability: If a measurement or test is reliable, it gives consistent results each time the activity is repeated. When undertaking an investigating a large number of repeats should ideally be taken, and any readings that vary considerably from the others (anomalous) should be repeated.

    Source:Collins Student Support Materials AQA AS BIO Unit 2 book
    Wow Collins Student Support Materials can't be very good if they are giving pretty much the same definition for both, muddling up Precision!

    A better way to think about it is that a ruler with Millimetre divisions is a more precise instrument than one with only centimetre divisions.

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