A-Level Experimental terms

• Control variables


  the variables you keep the same in an experiment
• Dependent variable


  the variable that is being measured when there is a change in the independent variable
• Independent variable


  the variable that is being changed deliberately to investigate the effects
• Validity


  Actually measuring exactly what you intend to measure
• How to increase validity

  -Ensure controlled variables-Experimental controlled condition-Larger sample size
• Precision


  a measure of how close a series of measurements/readings are to one another
• How to increase precision

  -increase sample size (calculate mean)-reduce effect of random errors-calibration-use same equipmentsystematic error does not increase precision as results still can be close to each other (precise), but just not accurate
• Accuracy


  A description of how close a measurement is to the true value of the quantity measured.
• How to increase accuracy

  -use equipment with higher resolution-larger sample size and then therefore calculate mean-read off the bottom of the meniscus-reduce systematic and random errors
• Difference between precision and accuracy

  Precision is values of repeated measurements are clustered and have little cluster. Accuracy is measured value is close to true value.

  
• Repeatability


  refers to the fact that a procedure can occur repeatedly through time achieving similar/same results
• How to increase repeatability

  -standardise method-remove subjectivity/ try use quantitative results rather than qualitative
• Uncertainty


  an estimate of how much a measured or calculated value differs from a true value
• How to decrease uncertainty

  -decrease systematic and random errors-take multiple measurements and calculate mean-use equipment with higher resolution/smaller intervals +- e.g. a caliper instead of a standard ruler
• Resolution


  Smallest change in the input quantity being measured by a measuring instrument that gives a perceptible change in the reading of the measuring instrumente.g. resolution of a ruler is 1mm
• What must you never mention in these experimental questions

  Human error (does not exist)
• Reproducibility

  The precision obtained when measurement results are obtained by different operators using different pieces of apparatus. A measurement is reproducible when similar results are obtained by students from different groups using different methods or apparatus. This is a harder test of the quality of data.
• Reducing random error


  Take multiple samples to reduce the spread of data (and calculate mean) and reduce random error effects.
• Reducing systematic error


  This can be done by recalibrating the instrument, assessing and controlling environmental conditions and taking multiple measurements using more than one observer.
• Anomaly (outlier)


  A value in a set of results that is judged not to be part of the inherent variation