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Unit 4 - Reasons for Anomalous Results
An anomalous result is one which does not fit the pattern.

Unit 4 - Reasons for Anomalous Results

Most experiments will throw out one or two anomalous results. In this GCSE Biology quiz we look at some of the reasons why.

Anomalous means something that doesn't fit the pattern. In these results - 5, 10, 15, 17, 25, 30 - 17 is an anomaly as it doesn't fit the pattern of going up in 5's. Identifying anomalous results and finding reasons for them is a crucial part of the evaluation of any experiment, not just investigations. If you can see no data that is anomalous, you should state that in your evaluation so that the person marking your work knows that you have considered it.

Sometimes, in biological experiments, it can be difficult to spot anomalous results. Using a scatter graph with a line of best fit is usually the most effective way. You can quickly see any pattern and spot if any of the points are a long way from it. These can then be identified as anomalous.

There are many possible explanations for obtaining anomalous results. Human errors can lead to data which is anomalous and a lack of precision whilst taking measurements is one possible explanation. Using inappropriate measuring equipment could create problems too. If a linear scale is marked only in cm, it will not be as accurate as one marked in mm because you will have to estimate any readings that fall in between the cm marks. If the equipment is not adjusted to zero correctly before starting the experiment, this can give rise to zero errors which can lead to anomalous data. But it's not just human errors that you need to consider - faulty equipment or even the method of the experiment could be responsible.

When discussing anomalous results in an evaluation, top grade candidates will be very specific when suggesting causes. They will say things such as 'the result at 25oC is higher than expected so the temperature might have gone up when I was taking the reading'. This shows they are using their general scientific knowledge to find reasons for the anomaly - they know that reactions work faster at higher temperatures.

Anomalous data is...
close to the mean value
not in agreement with the pattern
Anomalous data does not agree with the pattern of the rest of the data
Zero error is when the equipment is not set to...
the maximum value
the minimum value
a known starting value
the endpoint
You don't necessarily need to set equipment to zero, although it does make things simpler
A systematic error is due to...
the equipment used
random measurements
actual data
human error
Systematic errors lead to anomalous data which is repeated over and over again. This leads to data which can have a high precision but is inaccurate. The main problems can occur if you have to carry out your experiment over a period of several lessons as you may end up using different equipment each time. This will give different systematic errors for individual results
Systematic errors can be identified by...
changing the experiment
doing a different experiment
changing the key variable
This is a high level skill - if you plan to calibrate equipment in your investigation it would impress the marker!
If anomalous data is identified, the experiment can be repeated and this can be recalculated.
All parameters
You only need to repeat the experiment for the readings that were anomalous. If you do this, always include the value(s) of the anomalous data in the evaluation but not in your recalculations
Which of these pieces of equipment needs to be set to zero before use?
Bunsen burner
Top pan balance
Air currents can affect a balance so make sure it has settled after zeroing and re-zero if necessary
If data is inaccurate, we will do more...
Using different equipment can identify if the errors are systematic
Identifying these can lead to increased accuracy and reliability.
Most students will focus on human errors, higher level candidates will also try to suggest systematic errors too
A chart of this type can reveal anomalous data.
Flow chart
Pie chart
Scatter graph
Bar chart
A line of best fit will quickly show you any anomalous results
If scientists discover anomalous data, they will do this and take an average.
Repeat many times
Delete the bad data
Give up
Select a different experiment
Repeating the experiment many times and calculating the average can smooth out errors
Author:  Donna Maria Davidson

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