Analysing & Interpreting Data

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What does it mean to analyse and interpret data?

Data can be collected from many different situations. The data we collect are not much use without analysis and interpretation. The analysis involves finding patterns and trends. For example:

The graph shows that the height of the plants increased when fertiliser was applied.

The interpretation is where you show the explain what those patterns and trends mean.

Being able to analyse and interpret the results and to write a valid conclusion depends on a good understanding of the purpose of the investigation and of the scientific principles related to the topic being investigated.

This is where your research on the topic becomes important and you explain your results. Relationships should be stated clearly and concisely. Refer to the measurements as evidence, and draw conclusions from the data. Be sure that conclusions are supported by evidence.

Sometimes, it may be possible to explain data in more than one way. Your experiment may not always reveal the causes of your observations, so other explanations should always be considered. For example, if the leaves of a plant start to discolour and become yellow, it could indicate that the plant is suffering from a lack of water. It could also mean that the plant has a nutrient deficiency or a disease caused by an insect. It is important to consider alternative explanations when discussing data and analysing results.

Analysis of Quantitative and Qualitative Data

Quantitative Data

When quantitative data is collected and put on a graph, a trend or relationship can be explained in terms of the two variables shown on the axes.

A trend - identify the consequences of changing the independent variable, e.g. the larger the force the faster the speed of the trolley.
A relationship - show a quantitative link between the independent and dependent variables, e.g. when the force is doubled the acceleration of the trolley is doubled.

Qualitative Data

When qualitative data is collected, a comparison between the control and the experiment, or between features before and after, needs to be interpreted.

What does the difference between the control and the experiment show?

When to use the Mean, Median or Mode

There are three ways of describing the data midpoint:

Mean - the average.
1. - When measuring the midpoint, the mean uses all data points.
  - Use when the data is quantitative, symmetrical, and on an interval or ratio scale.
  - Symmetrical data means the data is not affected by extreme values, and that the mean, median and mode are very similar. Symmetrical data is close to a normal distribution where there are roughly equal values to the left or right of the median.
Median - the middle number when all of the readings are put in numerical order
1. - Use when the data is quantitative, skewed, and on an ordinal, interval or ratio scale.
  - Ordinal data is categorised and ranked, and there is a clear order or ranking among categories (e.g. satisfaction ratings, achievement level).
  - Skewed data means there are more values to the left or right of the median. Skewed data means the median, mean and mode are probably not equal.
Mode - the most common data point
1. - Use when the data is qualitative, nominal (describes variables without any quantitative value) and when the variables are discrete (countable and cannot be subdivided).

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Glossary

Key terms and definitions.

Reading Graphs

Drawing a line of best fit helps you see the trend or general pattern of the results. Then you can see the relationship between the input variable and the outcome variable.

You can also extend the line and to read off the graph and a PREDICTION of data. Extending the data beyond the plotted points is to EXTRAPOLATE (extra = outside). Extrapolating is best done where the trends are known and predictable. If the trend in the data is not known then extrapolating should not be done.

The line graph to the right shows the speed of an object that has been dropped from an aircraft. To find out the speed of the object six seconds after it was dropped, follow these steps.

Go to 6 seconds on the x-axis.
Follow this grid line up to the graph line.
Go across to the y-axis and read the value. It is 152 km h−1.
So after six seconds, the object was moving downwards at 152 km h−1.

To read between the points on a graph, the reverse can be done. For example, when is the object travelling at 100 km h−1? Following the green dotted line on the graph, the value on the x-axis is 4.1 s. So the object was travelling at 100 km h- 4.1 seconds after it was dropped.

Trends in Graphs

All graphs are drawn to show the relationship, or trend, between two variables. Some variables increase when another variable increases, and some variables decrease when another variable increases. These relationships produce trend lines with characteristic shapes.

Note that:

Variables that change in linear or direct proportion to each other produce a straight trend line.
A variable that changes exponentially in response to the other variable produces a curved trend line.
'Inverse' means that one variable decreases as the other variable decreases.

Analysing Data Thinking Questions

Amylase Story & Questions

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