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# Test yourself now

High marks in science are the key to your success and future plans. Test yourself and learn more on Siyavula Practice.

## 18.5 Chapter summary

• Data handling means gathering and recording information, and then presenting it in a way that can be understood easily and used by other people.
• The population is the entire group being studied.
• A sample is a subset of the population that represents the population.
• Bias is the over- or underestimating of an outcome in a data set.
• Tallies are a way of counting by drawing a short vertical line to record each item.
• The frequency is how many times an event or observation occurred.
• We can organise data by grouping data points into intervals (classes).
• Intervals are a range of values that are consistently defined and equal in size.
• The mean is the sum of a set of values, divided by the number of values in the set.
• The median of a data set is the value in the central position, when the data set has been arranged from the lowest value to the highest value.
• The mode of a data set is the value that occurs most often in the set.
• The mode can also be described as the most frequent or most common value in the data set.
• A bimodal data set has two modes.
• The range of a data set is the difference between the maximum value and the minimum value in the set.
• An extreme value (outlier) is a number in the data set that is not typical of the rest of the set. It is usually a value that is much greater or much smaller than all the other values in the data set.