Results tables
A results table keeps your data organised.
- The independent variable goes in the first column.
- Each heading has the quantity and the unit: "Mass of rust (g)". Units go in the heading, not after every number.
- Leave columns for each trial and the average.
- Use the same number of decimal places down a column.
| Temperature (°C) | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) | Average (s) |
|---|---|---|---|---|
| 20 | 62 | 58 | 60 | 60 |
| 40 | 41 | 39 | 40 | 40 |
| 60 | 26 | 24 | 64 | 25 |
| 80 | 15 | 16 | 14 | 15 |
Look at 60 °C. The third trial, 64 s, does not fit. It is an outlier. Leave it out of the average and repeat that trial if you can: .
Graphing data
- Independent variable on the x-axis, dependent variable on the y-axis.
- Label both axes with the quantity and unit.
- Use an even scale that fills most of the grid.
- Plot neat crosses, then draw a line of best fit (straight or a smooth curve). Never join dot to dot.
- Give the graph a title.
| Use a... | When the independent variable is... | Example |
|---|---|---|
| Line graph | A number that can take any value (continuous) | Temperature, time, mass |
| Column graph | A name or group (categorical) | Type of liquid, metal used |
Describing trends and patterns
A trend is the overall direction of the data. Describe it in words and use numbers.
- Positive trend: as x increases, y increases.
- Negative trend: as x increases, y decreases.
- No trend: no clear link.
- Directly proportional: a straight line through the origin. Double x and y doubles.
Good answer: "As the temperature increased from 20 °C to 80 °C, the dissolving time decreased from 60 s to 15 s. The decrease was larger at low temperatures."
Errors
| Error | What it does | Example | How to reduce it |
|---|---|---|---|
| Random error | Results scatter up and down unpredictably | Starting the stopwatch a little late or early | Repeat trials and average |
| Systematic error | Every result shifts the same way | A balance that reads 0.2 g with nothing on it | Fix or calibrate the equipment. Repeating does not help |
| Mistake | Human slip, gives an outlier | Reading 64 instead of 24 | Repeat that trial |
Parallax error happens when you read a scale from an angle. Always read a measuring cylinder at eye level, from the bottom of the curved surface (the meniscus).
Accuracy, precision, reliability, validity
| Word | Meaning | Improve it by |
|---|---|---|
| Accurate | Close to the true value | Calibrated equipment, removing systematic error |
| Precise | Repeated results close together. Also, an instrument with small divisions | Finer instruments (a 10 mL cylinder instead of 100 mL) |
| Reliable | Repeating gives similar results | More trials, averaging |
| Valid | Fair test that measures what it claims | Controlling variables |
Suggesting improvements
When asked to improve an experiment, pick the weakness and give a precise fix.
- Results scattered: more repeats.
- Big gaps between x values: more intervals in the range.
- Hard to see the end point: use a better end point (for example, a cross under the beaker that disappears).
- Readings too coarse: use more precise equipment.
- A variable not controlled: control it (for example, use a water bath to keep temperature steady).
- Independent in first column
- Units in headings
- Trials and average
- Line: continuous
- Column: categories
- Line of best fit
- Positive or negative
- Proportional: straight through origin
- Random: repeat
- Systematic: fix equipment
- Outlier: leave out, repeat
- Accurate, precise
- Reliable, valid
Quick summary
- Tables: independent variable first, units in headings, trials and an average.
- Leave outliers out of the average and repeat them.
- Line graph for continuous data, column graph for categories. Draw a line of best fit.
- Describe trends with direction and numbers.
- Random errors scatter results: repeat. Systematic errors shift all results: fix the equipment.
- Accurate means close to the true value. Precise means close together. Reliable means repeatable. Valid means a fair test.
- Improvements must be specific, never just "human error".
Quiz
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