To interpret indicator data, compare the values, describe the pattern with numbers, and say what the data does and does not show. Repeating the table in words earns nothing.
This lesson opens the environmental sustainability cluster. The next lesson, explaining pollution pathways, shows how to link a pattern to a cause.
What are the three steps of reading indicator data?
- Compare. Find the highest and lowest values and what each belongs to.
- Describe. Which way does the pattern go, and by how much?
- Limit. What would you need to know before saying why?
Do these in order. Students who jump to step 3 first tend to write a cause the data never showed.
Worked example: a fictional river
Dissolved oxygen was measured at four stations along an invented river on one morning, all using the same meter. Dissolved oxygen is the oxygen available to fish and other living things in the water.
| Station | Position | Dissolved oxygen (mg/L) |
|---|---|---|
| 1 | Upstream, forest | 8.2 |
| 2 | Beside a vegetable farm | 6.4 |
| 3 | Below a town drain | 4.1 |
| 4 | Further downstream | 5.3 |
Compare. The highest value is 8.2 mg/L at station 1 and the lowest is 4.1 mg/L at station 3.
Describe the pattern. The value falls from 8.2 to 6.4 between stations 1 and 2, a drop of 1.8, then falls to 4.1 at station 3. It rises to 5.3 at station 4, which is 1.2 higher than station 3 but still below station 1.
Limit the claim. The data shows that oxygen is lowest below the town drain. It does not prove the drain caused it, because only one day and one reading per station were taken. The assumptions are that the same meter and method were used at each station at about the same time.
The mistake that costs marks
The usual slip is “The town drain pollutes the river and kills the fish”. The table contains no fish data, and a single reading cannot name a cause.
A supported sentence is “Dissolved oxygen is lowest at station 3, below the town drain, which is consistent with waste entering the river there”. The words “consistent with” keep the claim inside the evidence. A fuller explanation of how waste lowers oxygen belongs in a pathway answer.
Reading a trend over time
The same steps work when the readings are weekly instead of by place. Suppose an invented pond has pH readings of 6.8, 6.7, 6.2 and 5.9 over four weeks.
The trend is a fall in pH, so the water is becoming more acidic. The total change is 6.8 − 5.9 = 0.9. Because the weeks are equal gaps, you can also say the fall sped up after week 2, since the drop from week 2 to week 3 is 0.5 while the first drop was only 0.1.
Check yourself
Using the pond readings above, write one sentence describing the trend and one sentence stating what cannot be concluded.
Answer
Trend: the pH of the pond fell from 6.8 to 5.9 over four weeks, a drop of 0.9, so the water became more acidic.
Limit: the data does not show what caused the fall, and it does not show any effect on living things, because only pH was measured. More readings and other measurements would be needed.
What to study next
Follow up with explaining pollution pathways, then try the environmental sustainability practice set. The graph evidence and fair-comparison lab gives more tables to read.
If you would like a teacher to go through your interpretations line by line, see online one-to-one Science tuition.