Stats 1 - Grouped data

If we had these data:

time taken:
10 - 19
20 - 24
25 - 29
30 - 39
40 - 54

I don't understand how we find the class width of the first and last, for the middle ones I understand how to get it (from what out teacher told us we in this case:

we add up the sum of the numbers between the red lines e.g. 19 + 20 then divide by 2

but I don't understand how the 10 - 19 would be 9.5 or how the 40 - 54 would be 54.5

thanks!

(edited 11 years ago)

Reply 1

ghostwalker

Original post by Secret.

but I don't understand how the 10 - 19 would be 9.5 or how the 40 - 54 would be 54.5

thanks!

It depends on how the data is defined.

If we've rounded to the nearest integer which would be the usual case, then yes, the class boundaries are 19.5 for example.

Our first lower class boundary would be 9.5 because that would round to 10, similarly our final upper class boundary.

Reply 2

Secret.

Original post by ghostwalker

Aah okay so usually it will be the upper bound of the first number in that first class?
e.g. if the data was:
1-20
21-30
31-40

our first one would be 0.5, second would be 20.5, third 30.5 and so on?

Reply 3

ghostwalker

Original post by Secret.

Aah okay so usually it will be the upper bound of the first number in that first class?

Don't follow that statement.

e.g. if the data was:
1-20
21-30
31-40

our first one would be 0.5, second would be 20.5, third 30.5 and so on?

Yep, those would be your class boundaries.

Reply 4

Secret.

Original post by ghostwalker

Don't follow that statement.

Yep, those would be your class boundaries.

Is it because it's not always that all the time? If not could you give me an example of when it isn't please :biggrin:

Reply 5

ghostwalker

Original post by Secret.

Is it because it's not always that all the time? If not could you give me an example of when it isn't please :biggrin:

Nope - I just didn't understand what you meant by "the upper bound of the first number in that first class"

Reply 6

Secret.

Original post by ghostwalker

Nope - I just didn't understand what you meant by "the upper bound of the first number in that first class"

Aah okay thanks very much! :biggrin:

Reply 7

Secret.

Original post by ghostwalker

Nope - I just didn't understand what you meant by "the upper bound of the first number in that first class"

Hi, sorry to be a pain but what if the class intervals were:

0 - 9
10 - 14
15 - 19
etc

what would be the value for the first interval (0 - 9) thanks!

Reply 8

ghostwalker

Original post by Secret.

Hi, sorry to be a pain but what if the class intervals were:

0 - 9
10 - 14
15 - 19
etc

what would be the value for the first interval (0 - 9) thanks!

What's the underlying data? Has it been rounded to the nearest whole number, or truncated so 4.9 is treated as 4, for example?

PS: Have a go yourself first.

Reply 9

Secret.

Original post by ghostwalker

What's the underlying data? Has it been rounded to the nearest whole number, or truncated so 4.9 is treated as 4, for example?

PS: Have a go yourself first.

It's been rounded to the nearest metre, also what would be the difference in the answer if 4.9 was treated as 4?

thanks so much :biggrin:

Reply 10

ghostwalker

Original post by Secret.

It's been rounded to the nearest metre, also what would be the difference in the answer if 4.9 was treated as 4?

thanks so much :biggrin:

As it's been rounded your first class boundaries would be -0.5 to 9.5 (yep, I know it goes below 0)

If 4.9 is treated as 4, then your first class boundaries would be 0 to 10.

Reply 11

Secret.

Original post by ghostwalker

As it's been rounded your first class boundaries would be -0.5 to 9.5 (yep, I know it goes below 0)

If 4.9 is treated as 4, then your first class boundaries would be 0 to 10.