P.07 Accuracy, Precision, and Replicates

Key Concepts in Measurements

1. Accuracy

• Definition: How close a measurement is to the true value.
• Example: In a temperature reading, if a calibrated thermometer shows 31°C when the actual temperature is 31°C, the reading is accurate.
• Factors Affecting Accuracy:
  • Calibration of the instrument (e.g., thermometers, pipettes).
  • Proper use of measurement techniques to avoid systematic errors.

1. Precision

• Definition: How consistently a measurement yields the same value each time under the same conditions, regardless of accuracy.
• Example: A thermometer that always reads 32°C when the actual temperature is 31°C is precise but not accurate.
• Importance of Precision:
  • Precision is valuable in comparing consistency in measurements.
  • It helps determine reliability in the measurement process, even if accuracy is lacking.

1. Replicates

• Definition: Multiple trials of the same experiment using identical materials and methods to improve reliability.
• Purpose:
  • Identifies variation in measurements and increases confidence in the results.
  • By calculating the mean of replicate readings, you get a more reliable representation of the expected outcome.
• Example in the Rennin Experiment:
  • Use three tubes with the same rennin concentration, measure the clotting time for each, and calculate the average.
  • If the readings are consistent, this suggests high precision; if they vary greatly, it indicates low precision.

Application in Experiments

1. Improving Accuracy:

• Calibrate Instruments: Ensure all tools (e.g., thermometers, pipettes) are calibrated correctly before taking measurements.
• Avoid Parallax Error: Position your eye level with the measurement scale to avoid reading errors.

1. Achieving Precision:

• Standardize Methods: Follow the same measurement techniques every time.
• Replicate Measurements: Take multiple readings of the same sample to assess the consistency of the measurements.

1. Using Replicates for Reliable Data:

• Set Up Multiple Samples: Repeat the experiment for each value of the independent variable (e.g., rennin concentration).
• Calculate Mean and Check for Outliers: Use the mean value of replicates for each condition to reduce the impact of any outliers or random errors.

Key Terms

Practical Tips for Measurements

• Use a Control:
  • Always include a control sample to verify the effect of the independent variable.
• Apply Consistent Techniques:
  • Handle equipment carefully and maintain the same conditions to improve both accuracy and precision.
• Document and Analyze Variability:
  • Note any variations in replicates and calculate means to enhance the reliability of your findings.

Using these practices in experiments helps ensure the data collected is dependable, enabling valid and reproducible conclusions.