1.8 Grouping continuous data
Earlier you used a grouped frequency table to organise the number of DVDs owned by school students. In a similar way, grouped frequency tables are needed for continuous data.
There is a slight difference in the way the class intervals are organised for continuous data. Since continuous data can take any values within a given range, you need to allow for this in your table, as follows.
Table 6 How long do you spend on your mobile phone each week?
|Hours (h) spent on phone||Tally||Frequency|
|0 ≤ h < 10|
|10 ≤ h < 20|
|20 ≤ h < 30|
|More than 30|
In this grouped frequency table we are using ‘less than’ and ‘less than or equal to’ notation.
Earlier, when discussing the discrete data example of DVDs, we discussed the importance of having no overlap in the categories. For this reason, the categories were 0–5, 6–10, and so on.
In this example, since time is continuous, we need to allow for values such as 10.5 hours. The first category includes 0 but does not include 10. This means that any value less than 10 hours will be included in the first row. This would include values such as 9.5 or 9.7.
In the second row, 10 is included but 20 is not. This means that any value which is between 10 (including 10) and 20 (not including 20) will go here.
This concept is covered towards the end of lower secondary school but learners in primary school will have seen the notation <, to mean ‘less than’ and ≤ to mean ‘less than or equal’ to. So, we can write 10 ≤ h < 20.