How do I write the Evaluation of a lab report?

Evaluate the method, not the scientist!

Evaluations can be difficult, that’s why they get you the top marks (or bump you up to the higher levels), especially if you start off evaluating the wrong thing. Just like in an essay or a presentation, you have to have a clear idea of what you are evaluating before you start brainstorming. People may feel strange pointing out weaknesses in the method they used for an experiment, especially if it is one that they designed themselves. However, this is exactly what you have to do, evaluate the Method, not the scientist (which is you or you and your lab partner)! 

Don’t worry though, this ABEL article will help you get the top marks and not make it sound like you are a terrible scientist. The first thing to be aware of is the trick of always referring to ‘the method’, rather than ‘I’ or ‘we’. It is always advised not to refer to yourself in lab reports anyway, but this is especially true when pointing out problems or mistakes that have been made. For example, you can say:

The method says that 3.5 g of copper(II) sulfate should be added to the mixture but this was too much.

This is much better than saying “We put too much in”. Another way to avoid sounding like a terrible scientist is to use the passive voice. This way of writing is normally used by scientists, who focus on the science, not the scientist. For example, you might say:

The 3.5 g of copper(II) sulfate added to the mixture was found to be too much.

You haven’t said who found this out, or who wrote the method, but you have clearly shown you have identified a problem with the method. The Evaluation should be based on problems you have noticed that might change the results of your experiment. Your conclusion is based on your results. If the results are not as precise or accurate as they could be, this will affect your conclusion, and therefore your marks.

As ABEL has already pointed out, by the time students start writing the Conclusion and Evaluation they are tired and these parts are often rushed, even though they can give you the most marks. This is one reason why it is best to start writing the Evaluation as soon as you start reading about/designing the experiment. 

As soon as the teacher says something in their introduction to the lab session, you read something in the online introduction or method, or you spot something as you are performing the experiment—write it down straight away!

It is very tempting to think “I’ll remember that and put it in the Evaluation at the end of the experiment or when I write it up”, but chances are you will forget. You might be tired, rushed, or distracted and it is very frustrating trying to remember those great points you had. It may even lose you marks. So don’t wait, keep track of all your ideas. You might only need to include three evaluation points, and you have five or six that you’ve written down. Great! Include more or choose the best three. It will increase the quality of your lab report.

What should go in the Evaluation?

An evaluation typical includes the strengths and weaknesses of something, the pros and cons, or advantages and disadvantages. You do this all the time, when you are deciding which cereal to buy, which phone to get, where to go at the weekend, but obviously in a lab report there is a specific way to do this. Again, this process overlaps with those in a scientific essay or presentation, but some mark schemes, schools, and syllabuses do not require scientists to report on the strengths of the method; they only award points (or levels) for identifying problems that may affect the results of the experiment. If you don’t need to identify any strengths of the method, skip the next section.

If you need to give examples of what parts of the method helped you to record accurate and precise measurements, this is where you would do this. In a real scientific paper, this would help you to “sell” the research and show people why your method is an improvement on other techniques. As a general rule, three strengths is usually sufficient, but always check the mark scheme or ask your teacher.

Read your method again, even if you noted some great points when you were designing or performing your experiment (see above). It is always better to double check, you might spot something even more helpful and relevant. Can you see any specific things you did that helped make your measurements for each IV value be quite similar? This would help your measurements be accurate.  What did you do that ensured your DV measurements are the closest to the actual results they could be (precise)?

For example, in the ABEL Writing Variables in a Lab Report Overview, we used the following example experiment:

The method describes how to fix a ruler in the tank so photos of the fish can be taken and the fish’s length can be measured. The method tells the reader how a box was stuck to the front of the tank so the camera was always the same distance away from the ruler, and at the same angle. If either of these two things changed, this would change the results (That’s why they are control variables). However, this is a clever way to control these variables, and something that is easily explained and repeated by other scientists. So you can definitely include these as strengths of the method. 

Strengths of the Method should therefore be one of these things:

1. Unique to your experiment or interesting

2. Help make the DV measurements precise or accurate

3. Be easily repeatable by other scientists

4. Use a simpler method/materials than similar experiments.

Remember to use the mark scheme/rubric/teacher’s advice to include the most relevant points for your school/age/education system. The above points are for evaluations in general, so you know what goes into a great lab report by the end of your school career. It is unlikely you will need to write something for all four points, so find out in advance and don’t worry if you can’t think of any strengths for all the above points.

All scientific reports, and academic writing in general, include a limitations section. You will probably only have to do this when instructed to by your teacher, after you have practised writing all the other sections (see ABEL’s overview of how to write a lab report). This is because everyone needs to be able to confidently write the other sections (which takes practice) and according to most mark schemes, the evaluation needs higher level thinking and so distinguishes the top scientists in the class, as is the difference between an 8/10 and a 10/10, an A and a B, or a 8/8 and a 6/8 — depending on your school.

We will now outline everything a great Evaluation has in it, but please remember that this is for a complete Evaluation, you probably won’t need all the parts until you do a final project when you are finishing your final year at school and need to be prepared for university. As above, remember to use the mark scheme/rubric/teacher’s advice to include the most relevant points for your school/age/education system.

Look again at the example table above, try to imagine doing the experiment. Can you think of any parts that might:

1. Make the DV measurements less precise or less accurate?

2. Stop the method being easily repeatable by other scientists?

3. Are more complicated than they need to be?

For example, you might say in your Evaluation that measuring the length of a fish, especially different types of fish, might not be the best way to record their growth. Fish grow in three-dimensions after all! Some might have used the energy in the food to grow wider or taller, rather than longer, and this wouldn't have been recorded in your results. 

So you might write something like:

Not all energy from the food is used to grow in length. The fish may have grown in height or width at different rates and this was not measured. 

You now need to suggest an improvement to the method. You probably aren’t going to do the same experiment again, but a standard way to start the sentence is:

To improve the method we will measure the mass of the fish by placing them in a small tank of water on a digital balance. This will allow us to record the mass in grams.

You should always try to think about these four kinds of sentences for each problem with the method. Even if you don't get marks for them now, it’s great practice and helps you in other ways. The four points to think about are:

• What is the problem?

• How might it change the results?

• What would you do next time to avoid the problem?

• Can you give a specific example of your solution?

Even if you can think of problems with your solution — your teacher will still have to give you the marks! 

Let’s look at one more example.

You might have done an experiment in school where you put pieces of potato into hydrogen peroxide to make bubbles of oxygen. You can visualise the bubbles by adding some washing-up liquid to the mixture. It’s a fun and interesting experiment and there are lots of different things you can change to see what affects the height of bubbles. Let’s look at an example method that investigates the effect of temperature on the reaction:

Objective

To study the effect of temperature on the activity of catalase enzymes.

Materials 

Potato, Thermometer, Beaker, Ruler, Water bath, 5 test tubes, Stopwatch, Washing-up liquid, 

Test tube rack, Ice, Goggles, Dropper pipettes, Pipette, Hydrogen peroxide (H2O2)

Method 

1. Place five test tubes in a rack.

2. Fill each test tube with 5 mL of H2O2 and 5 mL of water.

3. Using a clean dropper pipette, add 2 drops of soap to each test tube.

4. Heat/cool tubes to correct temperature.

5. Cut 5 cubes of potato.

6. Add one of the cubes to the first test tube and begin timing with a stopwatch. 

7. Measure the froth length after 3 minutes of enzyme catalyzed reaction.

8. Repeat at another temperature.

As you do the experiment in the lab, you will probably think of some other points to add to the evaluation, but just by reading the method we can identify some things that might change the results. Can you think of a problem with the above method? How might it change the results?

What would you do next time to avoid the problem, giving a specific example of your solution?

You will notice that:

• The Method isn’t very specific — it would be difficult to follow without needing to know some more details. Do you think it would get top marks?

• A positive point is that iIt is quite short and simple, it is not overly complicated.

Perhaps the most obvious problem is in Step 5, cutting the potato cubes. The pieces obviously have to fit into a test tube, but how big should they be? Changing the size may well affect the reaction, so you may write something like this:

Because the method does not specify the size of the potato cubes, each cube can be cut to a different size. This means each reaction has a different surface area of potato in it and a greater surface area will increase the rate of reaction. This means it is an unfair test as the results will be affected. To solve this problem, I will include a size of potato cube in the method, for example 1 cm2. If each side of the cube is cut to 1 cm, this will be easy to measure and all the cubes will be the same size.

This is quite a complete answer to the problem in Step 5, but for the whole evaluation. You only need three paragraphs like this to get full marks for this section. 

With practice, you will have identified the three problems before you start writing the lab report, have a good idea of solutions to the problem, and you will be able to easily write this section knowing what your teacher is looking for. 

Here, you can see an example of a complete lab report, that contains a comprehensive evaluation, or download a template for lab reports to let ABEL help you get the top marks!

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