Unit 4 AOS 3 Flashcards
define true value
The value that would be found if the quantity could be measured perfectly.
is it possible to get the true value exactly?
In reality, it is impossible to obtain the true value of any quantity since there will always be variations and errors.
define accuracy
A measurement value is considered to be accurate if it is judged to be close to the true value of the quantity being measured.
what type of term is accuracy?
Accuracy is a qualitative term
define precision
A measure of the repeatability or reproducibility of scientific measurements and refers to how close two or more measurements are to each other.
how is accuracy described in relation to a true value?
a measurement value or measurement result may be described, for example, as being ‘less accurate’ or ‘more accurate’ when compared with a true value
what do precise measurements have in relation to the mean value?
A set of precise measurements will have values very close to the mean value of the measurements.
does precision give indication of true value?
Precision gives no indication of how close the measurements are to the true value and is therefore a separate consideration to accuracy.
define Measurement result
Refers to a final result, usually the average of several measurement values.
what is the measurement result when there is only one value?
In the (unusual) case where only one value has been measured, then measurement result also applies to that single measurement value.
define repeatability
The closeness of the agreement between the results of successive measurements of the same quantity being measured, carried out under the same conditions.
what conditions are the same for repeatability?
→ observer
→ measurement procedure
→ measuring instruments
→ used under the same conditions, over a short period of time
what experiments may yield results that are not repeatable?
Experiments that use subjective human judgement(s) or that involve small sample sizes may yield results that may not be repeatable.
what can repeatability be used for in analysis?
Repeatability can be used to evaluate the quality of data in terms of the precision of measurement results.
what should measurements be in relation to repeatability?
Ideally, measurements should be repeated where possible to produce a measurement result.
define reproducibility
The closeness of the agreement between the results of measurements of the same quantity being measured, carried out under changed conditions of measurement.
what conditions are different/changed for repeatability?
→ different observer
→ different measurement procedure
→ different measuring instrument
→ used under different conditions, carried out at a different time.
what is the purpose of reproducing?
The purposes of reproducing experiments include checking of claimed precision and uncovering of any systematic errors that may affect accuracy from one or other experiments/groups.
what experiments may yield results that are not reproducible?
Experiments that use subjective human judgement(s) or that involve small sample sizes or insufficient measurements may also yield results that may not be reproducible.
do small changes in experiments effect the results (resolution)?
- The smallest change in the quantity being measured that causes a perceptible change in the value indicated on the measuring instrument.
- This has implications for determining the number of decimal places to which a quantity may be quoted.
define validity
A valid experiment investigates what it sets out and/or claims to investigate.
what should be considered when evaluating validity?
Both experimental design and the implementation should be considered when evaluating validity.
how can an experiment not be valid?
An experiment and its associated data may not be valid, for example, if the investigation is flawed and controlled variables have been allowed to change. Data may not be valid, for example, if there is observer bias.
what do random errors affect?
Affect the precision (or repeatability) of a measurement and may be present in all measurements.
define random errors
Random errors are unpredictable variations in the measurement process and result in a spread of readings (both above and below the true value).
what helps minimise random errors?
→ more trials will generally help average out random errors
what do systematic errors affect?
Affect the accuracy of a measurement and will likely be present in all measurements.
define Systematic errors
Systematic errors often result from the quality or calibration of measuring equipment or experimenter bias. They result in a skew in readings (either all above or all below the true value).
do more trials help average out systematic errors?
→ more trials will not help average out systematic errors
define mistakes/personal errors
Also known as personal errors. (eg. you stuffed up the data collection).
should personal errors be included?
Mistakes should not be included in reporting and rather, the experiment should be repeated correctly.
define repeated measurements
Also known as trials.
what do repeated measurements/trials help with?
Are made to reduce the effect of random errors (and reduce the likelihood of mistakes).
define outliers
Data points or observations that differ significantly from other data points or observations.
what do you have to do when you have an outlier?
Outliers in data must be further analysed and accounted for, rather than being automatically dismissed. Repeating readings may be useful in further examining an outlier: for example, to determine whether the outlier is a personal mistake.
