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165 pagesrevision 46935
printed 156 · PDF 157
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156
Table 1: People Age and Frequency Distribution
People Age
Frequency
19 - 29
21
29 - 34
10
34 - 39
22
39 - 44
22
44 - 49
14
49 - 54
11
54 - 60
8
Total
108
examples we previously looked at for mean and mode were un-grouped data.
Now to calculate the mean, follow the steps:
3
1. The formula to calculate mean for
grouped data is:
P
Pf
imi
f. This means:
you are going to calculate the midpoint of each interval and make a sep arate
column of that, then multiply each of those midpoints m with the frequency
column respectively to calculate fimi after which sum them all together. This value
that you get, divide it by the total of the frequency, which in the Table [1] is 108.
To calculate median, the step are as follows:
1. Find Pf which is 108 (the total of the frequency) and then apply and the even-
odd rule for it
2. Then find the cumulative frequency for the dataset by adding each of the
consecutive frequencies and adding it in front of the new frequency’s row.
3. Next see between in which row does your median lie
4. That row is your answer for the median since for grouped datasets, at IGCSE
level, we cannot find the exact median value in it
2.3 Modal Class in a grouped frequency distribution
To calculate the modal class, simply see which distribution range has the highest
frequency value - that is your answer.
2.4 Spread of a Data
The spread of a data refers to how spread out from the central point the data is.
Let’s say the central point is 50 so if we have data that is 49,49,48,51 it’s very
close to the central point so it’s not very spread out. On the other hand, if we had
data like 101,1000,2000,300 then we would say it’s very spread out - has a
greater standard deviation (you don’t need to know this term at IGCSE level)
3 Statistical Charts and Diagrams
The charts you need to know are all displayed below with their keys to help you
understand better.