7.6 - Drawing Conclusions
What a conclusion question looks like
- Exam questions often give results in a table or graph and ask you to state a conclusion.
- A conclusion is not just a single reading from the table. It must answer the aim of the investigation by linking the two variables together.
What a conclusion must do
A complete conclusion does two things:
- Names both variables - The variable that was changed and the variable that was measured.
- States the relationship between them - How changing one affects the other.
For example: "As the height of the ramp increased, the speed of the trolley at the bottom increased."
A typical question
A student released a trolley from two different heights on a ramp and measured its speed at the bottom each time. The results are shown in the table. State a conclusion the student can make from these results.
Writing and evaluating conclusions
- A conclusion answers the aim by stating how the variable you changed affected the variable you measured.
- The most reliable structure to use is:
As the [variable you changed] increased, the [variable you measured] increased (or decreased).
For example: "As the height of the ramp increased, the speed of the trolley increased."
Common errors
- Quoting a single reading - Writing "the speed was 1.8 m/s" gives a value from the table, not a relationship between two variables.
- Naming only one variable - Writing "the speed increased" doesn't mention what caused the increase.
- Reversing the statement for a second conclusion - When asked for two separate conclusions, writing the same relationship backwards (e.g. "as the ramp got lower, the speed decreased") doesn't count as a new point.
Valid and invalid conclusions
- A conclusion is valid when the data support it and the investigation was a fair test (all other variables were kept constant).
- A conclusion is invalid when:
- The results don't support the claimed link.
- Key variables weren't controlled.
- It goes beyond what was tested (e.g. claiming a trend continues past the range of values actually measured, or applies to all objects).
Common exam questions
Question 1
A student investigated how the length of a wire affects its resistance. With reference to the aim, give a conclusion for this investigation.
As the length of the wire increased, its resistance increased. Both variables are named, the direction is given, and it answers the aim of finding how length affects resistance.
Question 2
A table gives the average stopping distance of a car on a dry road and on a wet road. Using this information, give a conclusion.
The stopping distance is greater on a wet road than on a dry road. The conclusion links the road condition to the measured stopping distance rather than just quoting one value.
Question 3
A student wrote: "as the height of the ramp increased, the speed increased, so a higher starting point always makes any object faster." Is this conclusion valid or invalid, and why?
Invalid. The data support the link for the trolley that was tested, but the claim about any object goes beyond what was investigated, so the conclusion cannot be extended that far.
Question 4
A student concludes "the speed was 1.8 metres per second". Why does this not score as a conclusion?
Because it quotes a single reading and never mentions the variable that was changed; a conclusion must link the two variables, for example "as the height of the ramp rose, the speed of the trolley rose".
Question 5
A resistor obeys Ohm's law up to a point, then the wire heats and the current stops rising as fast. Why can you not write "the higher the potential difference, the higher the current, always"?
Because the relationship does not hold across the whole range; the conclusion must match what the results actually show, including where the pattern changes.
Question 6
A question asks for a second, different conclusion. Why does "as the ramp gets lower, the speed falls" not earn it?
Because it is the first conclusion written backwards, not a new point; a second conclusion has to add something different, such as identifying the height at which the speed stopped increasing.