Cumultative frequency graph

baldy

When you plot a cumulative frequency curve should the line go through the origin (0,0)? Thanks!

Reply 1

Chewwy

17

baldy

When you plot a cumulative frequency curve should the line go through the origin (0,0)? Thanks!

if the cumulative frequency at 0 is 0, then yes.

Reply 2

baldy

OP

chewwy

if the cumulative frequency at 0 is 0, then yes.

Thanks for replying. Sorry to be a little ambiguous in the question - here goes again...

Out of a set of 6 data; if the first class width is say 20 - 30 with a frequency of eg: 8 mph ie: first plot from data given is at cf = 8 and speed = 30, and so on for the rest of the data: Query is whether to extend the lower portion of the curve (left hand end) back to cross the x axis at 0 or just with a natural curve or straight line from 30, 8 to perhaps 20, 0 if going with the natural flow ? ie; if not given the data where x or y = 0 do you automatically return the curve to 0 , 0 anyway?

Reply 3

manps

baldy

Thanks for replying. Sorry to be a little ambiguous in the question - here goes again...

Out of a set of 6 data; if the first class width is say 20 - 30 with a frequency of eg: 8 mph ie: first plot from data given is at cf = 8 and speed = 30, and so on for the rest of the data: Query is whether to extend the lower portion of the curve (left hand end) back to cross the x axis at 0 or just with a natural curve or straight line from 30, 8 to perhaps 20, 0 if going with the natural flow ? ie; if not given the data where x or y = 0 do you automatically return the curve to 0 , 0 anyway?

I think, in this case the c.f on the y axis will go from 0 to whatever it goes up to and then on x it will start at 20 and increase in the intervals stated. So your first plot is, (20,0) because at 20 your c.f is nothing, i.e you havent counted any yet, your next one is at (30, 8), you have to plot it at the end of the interval because you dont know where the data is from. You should join the points together and usually you end up with a diagonal enlongated S shape curve.

Regards

Reply 4

the bear

20

it does not have to go through the origin...for instance if the data was weights (kg) of hairdressers and the intervals were 0 to 20, 20 to 40, 40 to 60, 60 to 80 etc then you would not have any hairdressers in the first interval. the first point to plot would be (20,0) not (0,0)

Reply 5

baldy

OP

Thanks for taking the trouble to reply, that's a great help.

Cumultative frequency graph

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