(Edited so it is better understood.)
This way of grouping frequency distribution?
Age of mother f
15 up to 20 7
20 up to 25 36
25 up to 30 23
30 up to 35 18
35 up to 40 10
40 up to 45 6
I am in a dilemma. My question is, for example, a mother with an age of 20, where was her age placed? In the first interval or the second? How do we qualify if the mother’s age should be in the first interval or in the second interval? I would assume it is valid to place that range value (20) in two intervals, that 20 is the upper limit of the first interval and at the same time the lower limit of the 2nd interval, same with 25 in the 2nd and 3rd interval, and so on because it is written in a very popular book by a prestigious and high standard publisher.
So far, my understanding of grouped frequency distribution is limited to the following format only, where a value can exist in only one interval or grouped frequency.
Age of mother f
16 up to 20 7
21 up to 25 36
26 up to 30 23
31 up to 35 18
36 up to 40 10
41 up to 45 6
Or if the values involve decimal, (probably includes months and days and hours) in my papers, I report them as such. Like for example;
Age of mother f
15.001 up to 20 7
20.001 up to 25 36
25.001 up to 30 23
30.001 up to 35 18
35.001 up to 40 10
40.001 up to 45 6
At the back of my mind, it doesn’t make sense that a value exists in 2 intervals. In this case, these values seem confused for me… they don’t know where they belong. Age 20 for example doesn’t know if it belongs to the first interval or the second.
Please help me understand where I am lost or if I am missing something.
Age is a real-valued statistical feature (e.g. if a mother is 20 years and one day old, it can be expressed as 20+(1/365)=20,0027 years). So, a mother has a little chance to have exactly 20 or 30 years, and she'll probably fall into first or second class (15-20 or 20-25).
But, for those rare cases (if someone has a birthday) it can be set nominal class limit that declares whether the exact round value (20, 30, 40) falls into first or second class. You can establish a class that encompasses all mothers with age from exactly 15 years to 19.999 years. Second class would be from 20 to 24.999 years and so on. Corresponding nominal class limits, which you would write in the table, would be from 15 to 19, 20 to 24 and so on. You can also make the opposite classification (exact 15.001-20, 20.001-25 etc.; nominal 16-20, 21-25 etc.).
The most important thing is that you know these relations and let the others to know it.
Exactly what's at the back of my mind Tomislav. But the given data is what they are. Only age (in ratio scale btw). no birthdays. In decision-making, I just want to know how to decided that a value should fall in the 1st interval or the 2nd interval. I do think however that there is something wrong with this illustration but I would assume it is valid because it is written in a very popular book by a high standard publisher. I just need to know what I am missing.
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