Accuracy:**** How close your experimentally derived number is to the “true” or “real” quantity being measured. This relies on scale.
Precision: How close the repeat values or a given trial are to each other, OR the fineness of the scale on the instrument being used to take measurements
Reliability: If we conduct more trials and find that the results we get each time are not significantly different from the others
Validity: No other variables, known or unknown, are impacting the independent or dependent variables (fair tests)
Uncertainty/Error
Measurement uncertainty: uncertainty which is a property of the measuring instrument
- Unavoidable, quantifiable, hopefully very small
Systematic Error: Impacts each trial in the same direction away from the true value
- Bias in direction
Random Error: Impacts each trial but with no bias in direction, and if truly random, should cancel out with respect to accuracy
Absolute uncertainty(AU):
- A.k.a. Measurement Uncertainty
- A fundamental property of any measuring instrument
- Equal to the smallest increment of scale
- E.g., 30 cm ruler with 1 mm increments, AU is ± 0.005 cm
Relative/Percentage Uncertainty(%U)
- A property of the measurement taken
Rules for Calculating Error in compound measurements
- If multiplying or dividing, add %U together
- If adding or subtracting, add AU together