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quick s1 question

this is probably really dumb but i shall ask it anyway ~

for a table that shows grouped data, where the values are presented as say 90-139, 140-149 blah blah, would the midpoint be between the values shown (so, (139+90)/2 ) or between the class intervals ( (139.5+89.5)/2 )?

also, if plotting a histogram with this data, i guess i'd end the bars at 90, 140, 150 etc instead of the actual class boundaries right? :I

(edited 10 years ago)

Reply 1

Air1337

Midpoint would be between the class intervals so as you said ((139.5-89.5)/2) which is 25 and then we do 139.5 + 25 which is 164.5, this is the midpoint.

In histograms, data is continuous therefore we have to use 89.5 - 139.5, 139.5 - 149.5, etc.

Reply 2

PurpleSquid

Original post by Air1337

haha, i meant to write (139.5+89.5)/2 but it results the same answer anyway
hope i don't make that mistake in the exam :colondollar:

the thing is that the 2 histogram examples in the textbook seem to show the bars ending at an integer - even one from a table of values that should have class boundaries of .5
:s-smilie:

should i just plot the class intervals anyway (if a question does come up on the exam)?

Reply 3

Air1337

Original post by PurpleSquid

haha, i meant to write (139.5+89.5)/2 but it results the same answer anyway
hope i don't make that mistake in the exam :colondollar:

the thing is that the 2 histogram examples in the textbook seem to show the bars ending at an integer - even one from a table of values that should have class boundaries of .5
:s-smilie:

should i just plot the class intervals anyway (if a question does come up on the exam)?

You can plot the axis with whole integers but when it comes to plotting the bars of the histogram we have to use the class boundaries of 0.5 otherwise it wouldn't be continuous. Do you have the Edexcel textbook, if so, what page?

(edited 10 years ago)

Reply 4

PurpleSquid

Original post by Air1337

page 70 (above where it says example 11).
and page 74 (question 5, although the actual data isn't shown so the boundaries could have been whole numbers)

i think you're right though.

Reply 5

Air1337

Original post by PurpleSquid

page 70 (above where it says example 11).
and page 74 (question 5, although the actual data isn't shown so the boundaries could have been whole numbers)

i think you're right though.

The book uses 500.5 as the boundary between 301-500 and 501-800, the values are simply too high for us to notice it since 0.5 would be extremely small in that histogram.

Reply 6

PurpleSquid

Original post by Air1337

The book uses 500.5 as the boundary between 301-500 and 501-800, the values are simply too high for us to notice it since 0.5 would be extremely small in that histogram.