1. GUIDANCE Connecting Science © Hodder Education 2009 Evaluating a practical technique When we evaluate our method and results, we reflect on what we did and judge whether it was successful. Then we say how we would improve the technique.

2. GUIDANCE Connecting Science © Hodder Education 2009 Were there problems with the plan? We tested the effect of increasing the number of batteries on how bright the bulb was. The more batteries, the brighter the bulb. Do you think we should have measured the brightness of the bulbs? Here, for example, should the plan have included measurements as well as observations?

3. GUIDANCE Connecting Science © Hodder Education 2009 How we investigated the question For example, sometimes the variables chosen for testing might not have been the right ones to answer the question. Can we answer the question if we have not kept some things fixed? (Made it a fair test.) If we were testing bulb brightness with different numbers of batteries, would it have been a good plan to use both these types of battery?

4. GUIDANCE Connecting Science © Hodder Education 2009 Choosing a range and sensible values We chose the values of the the independent variable (the variable we controlled). Time in minutes Temperature in foam cup in °C Temperature in metal cup in °C 26360 35853 64641 In this heat experiment, we chose to measure the temperatures at 2, 3 and 6 minutes. But the range should always include the starting point (here, when time = 0). It would also have been better to choose to measure at equal time values (at 1, 4 and 5 minutes, as well).

5. GUIDANCE Connecting Science © Hodder Education 2009 Comment on the measurements and the way we used equipment Scientists know that you have to make sure there are enough measurements to answer the question. The measurements also have to be precise and reliable. There should be few errors. Time in minutes Temperature in foam cup in °C Temperature in metal cup in °C 26360 35853 64641 A bigger range of measurements (beyond 6 minutes) would help to show whether there is a pattern.

6. GUIDANCE Connecting Science © Hodder Education 2009 Precision of equipment There are measuring instruments with different ranges. The large measuring cylinders here don’t allow measurements to the nearest 1 millilitre. They are not as precise. There are measuring instruments with different scale intervals. range is the maximum reading

7. GUIDANCE Connecting Science © Hodder Education 2009 Evaluating precision Did we read the scale to the smallest scale division? (In this case, it is the nearest 10, not the nearest 50.) Did we choose the best apparatus to give precise measurements? nearest 50 nearest 10

8. GUIDANCE Connecting Science © Hodder Education 2009 Accuracy and measurement errors Anybody can make a mistake when they make a measurement. These are human errors. For example, it’s difficult to stop a timer at exactly the right moment. If a measuring instrument is well made then it should measure very closely to the true value (if we use it correctly!) If the measuring instrument is faulty, there are instrument errors. The measurement is not close to the true value – it is not accurate.

9. GUIDANCE Connecting Science © Hodder Education 2009 Evaluating errors Did we get similar results when we repeated the experiment? This is a check on the reliability of the data. The measurements could still be inaccurate if we used a faulty measuring instrument.

10. GUIDANCE Connecting Science © Hodder Education 2009 Identifying errors Can we identify odd-looking (anomalous) results? The 3rd reading looks odd. It looks as though the person making the measurements did not zero the stopwatch between the 2nd and 3rd readings. It would be better to ignore the 3rd reading.

11. GUIDANCE Connecting Science © Hodder Education 2009 Identifying anomalies Should these be included, left out or repeated? It would be best to repeat them and also get further data in between. The first six points show a straight line pattern but the other two points don’t fit the pattern.

12. GUIDANCE Connecting Science © Hodder Education 2009 Improving the method It can be a good idea to alter the method if we notice the equipment or the way of using it could be improved. Be we must be careful – if we changed the method in the middle of the enquiry, can we still compare the results and draw a proper conclusion?

13. GUIDANCE Connecting Science © Hodder Education 2009 A good evaluation might include these points: Was it a fair test? Were there variables that were not easy to control? Where could we have made errors? Were our results reliable? Are there enough results to show a pattern? Did we use a good range for our independent variable, or have a good sample size? Were the values we chose for our independent variable sensible, or did preliminary tests show that we needed to change the range or the amounts? Were there any odd results and what shall we do with them? What improvements can I suggest?