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EMPA (Unit 3) Revision Booklet

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Things to always include on tasks 1 & 2:
An informative title (describe what the data shows)
Descriptive headings
The units (only one type) in the form "pulse rate /bmp"
First column containing the independent variable (the
thing that is constant)


The time taken for starch to be…

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Calculations in Data Processing

There are three forms of processing data that depend on what
data is available to when you use them.

1. The mean

This is calculated when more then one repeat has been done.

Calculate the sum of the X values and divide it by the number…

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Standard Deviation

This measures the spread of data, and it can only be calculated
when there is more than one repeat.

The larger the standard deviation, the more widely spread the
data is and therefore you have a less reliable mean.

You can compare the standard deviation of two different…

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Which Graph to Draw?

Bar Chart

Use this when the controlled variable:
Is non-numerical


Use this when the controlled variable:
Is numerical
Classified into groups

Line Graphs

Use this when the independent and dependent
variable are:

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It is used to show relationships that are unapparent from

Use logic to determine which to use, it's usually straightforward.


In scatter diagrams:
The more data points, the more reliable the line of best
fit s
A line of best fit may be drawn if there is an…

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When answering questions always state the type of correlation.

If you are evaluating, use the phrase "correlation does not
prove causation, there may be other factors involved for
example...(and give an appropriate example!)."

Never join points by a line of best fit, as you can never be sure
of intermediate…

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2. Always put the units and a brief description on the axis

3. Use a suitable scale so more of the graph is used. Use a
line break if necessary.

4. Have equal intervals between all values.

5. DON'T use circles as points; use crosses as they are more

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Improves reliability.
A more reliable mean can be
Repeatability calculated.
Anomalies can be identified and
their effect on the mean reduced.
Monitoring a Constantly recording the values of
Variable the variable.
A variable that affects the outcome
that is not the dependent variable.
It should be monitored.

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Validity ­ Data is valid if the measurements have been made
by a single independent variable only. Controlled experiments
and no bias make results valid.
Repeatability ­ This makes results more reliable.
Accuracy ­ A measurement close to the true value.
Precision ­ Very little spread around the mean value.…


Joanna Ly


did you mean independent variable is the thing that changes?



really helpful thanks 

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