## 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.