Lesson 4: Ensuring Reliability: Repeats, Sample Size & Averaging
Carrying out a practical biological investigation with direction into a biological context.
🎯 Ngā Whāinga Akoranga | Learning Intentions
The importance of trial repetition (minimum 3 trials per IV value) to reduce random error, calculate mean averages, and detect anomalous outlier data.
Construct a raw data table with repeat trials (Trial 1, 2, 3), identify and omit anomalous outliers, and calculate mean values.
🎥 Media Anchor & Pedagogical Scaffold
Experimental Reliability & Data Outliers
Video Clip: GCSE Working Scientifically — Repeatability and Reproducibility: what they mean and why they matter (Freesciencelessons) (Runtime: 3m 51s).
🧠 1. Before Viewing (Activate & Predict)
Why is performing a single test at each temperature insufficient to draw a valid biological conclusion?
👁️ 2. During Viewing (Watch With a Job)
- Define: what is the difference between REPEATABILITY and REPRODUCIBILITY? Use the video's definitions.
- Repeats and averages: how many repeats does the video recommend for a reliable result? Why does calculating a mean improve reliability?
- Apply: if your biology investigation has very different values between three repeats, what does this tell you? What should you do before writing your mean?
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Demonstrate live data entry showing how a single timing error distorts results if unrepeated.
Immediate Task: Complete Section 4 of your Investigation Log: Raw Data Table Template & Reliability Protocol.
⚡ Whakaoho | Do Now: Investigation Recall (10 mins)
One result is an anecdote. A pair reports that at 30 °C their reaction took 12 seconds. Another pair, same setup, records 12, 13 and 41 seconds.
Two minutes: which pair knows more? Say what the 41 tells you that a single reading never could, and decide — before you are taught the rule — whether it should be included in the average, and on what grounds.
📖 Activity 1: Investigation Planning & Practical Execution (25 mins)
Build the table (12 min). Construct a raw data table with Trial 1, 2, 3 and a mean column, one row per IV value, units in the headers not in the cells. Then enter the class data provided.
Hunt the anomaly (13 min). Calculate means. Identify any anomalous value, and justify keeping or excluding it using the other two trials — not by whether it looks wrong. Then recalculate. Answer: how much did the mean move, and does that change your conclusion?
📝 Activity 2: Level 1 Biology Investigation Log & Merit/Excellence Scaffolding (20 mins)
Report — Section 4. Submit: (1) a correctly headed raw data table with three trials and means; (2) your anomaly decision with the reasoning and both means shown; (3) a sentence on how many repeats you would run given more time, and what that would buy you.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 1 Alignment: Direct preparation for NCEA Level 1 Biology — Internal (Carry out a biological investigation with direction). Emphasise complete variable control, accurate data processing, and clear biological explanations for Merit/Excellence grades.