Carrying out the project: plan, do, check
Take your plan from the earlier stage and work in short rounds.
- Plan the next small piece (for example "measure 8 plants on Monday").
- Do it in the same way every time.
- Check: did it work? Is the data sensible? If not, change the plan.
Keep a project log: date, what you did, what you saw, what went wrong, what you changed. Keep your time plan with small deadlines, keep your tools safe, and ask a teacher or expert when you are stuck. Keep copies of your files.
Collecting and recording data
Write results at once, with the unit, the date and how you measured. Make a table with a clear heading for each column. Repeat each measurement several times, because one measurement can be wrong. For a survey, ask the same questions in the same words to enough people, and keep names private. For a product, model, event or artwork, record tests and feedback: who tried it, what happened, what they said.
Checking the data honestly
An outlier is a value far from the others. It may be a typing mistake, a measuring error, or a real surprise. Find out which. Write it in the log. If it is a proved mistake you may leave it out, but you must say so in the report. Never remove values just because they do not match your hypothesis. Honest results are worth more than nice ones.
Analysing: mean, median, range, percent and charts
- Mean = sum of values ÷ number of values.
- Median = the middle value when the values are in order (for an even count, the mean of the two middle values). The median is not pulled much by an outlier.
- Range = largest − smallest. It shows how spread out the data is.
- Percent = part ÷ whole × 100. Percent change = (new − old) ÷ old × 100.
Choose a chart that fits: a bar chart to compare groups, a line graph for change over time, a pie chart for shares of a whole. Label axes with names and units, give a title.
Drawing conclusions and naming limits
Put your result next to the hypothesis or goal. Say: "The data supports / does not support the idea because ... (give numbers)". A result that does not support your idea is still a good result. Then write the limits (small sample, one place, short time, tool error) and the next step (more trials, a better tool, another group). Do not claim more than the data shows: "plants with more light grew taller in our test" is better than "light always makes plants taller".
Try it
Mini-experiment (10 minutes). Drop a ball from the same height 8 times and time the fall with a phone stopwatch. Write each time in a table. Spot any odd value, find the mean and the range, and make a bar chart. In the 3D above (step 5), move the slider to see how more measurements steady the mean. Write one sentence of conclusion and one limit.
Key formulas and definitions
- Mean = sum of values ÷ number of values
- Median = middle value of the ordered list
- Range = largest − smallest
- Percent = part ÷ whole × 100
- Percent change = (new − old) ÷ old × 100
Worked examples
1. Find the mean of the plant heights 12, 14, 13, 15 cm.
Sum = 12 + 14 + 13 + 15 = 54. Number = 4. Mean = 54 ÷ 4 = 13.5 cm.
2. Find the median of 3, 9, 4, 8, 5.
Order: 3, 4, 5, 8, 9. The middle (third) value is 5. Median = 5.
3. 18 of the 24 students surveyed liked the new timetable. What percent is that?
18 ÷ 24 × 100 = 75%.
4. The eight values 12, 14, 13, 15, 13, 14, 13, 15 have a ninth value 40 added. What happens to the mean?
Before: 109 ÷ 8 = 13.6. After: 149 ÷ 9 = 16.6 (about). The single odd value raised the mean by 3 cm. That is why we check the data before we calculate.
5. Plants in the dark average 13.6 cm; plants in light average 17.0 cm. Find the percent change.
(17.0 − 13.6) ÷ 13.6 × 100 = 3.4 ÷ 13.6 × 100 = 25%.
6. Your data does not support your hypothesis. What should you write in the conclusion?
Say clearly that the data does not support the hypothesis, give the numbers, and suggest reasons and limits (sample size, conditions). Do not change the data. A clear "no" with evidence is a good result.
Common mistakes
- Writing data later from memory. Record at once with the unit and date.
- Quietly deleting a value that spoils the pattern. Explain it in the log and the report.
- Using the mean when there is a big outlier and not checking it. Check, and also compare the median.
- Claiming more than the data shows, such as "always" or "proves". Say "in our test" and give numbers and limits.