Question

help me!
quick stats question
X f
5.5 4
15.5 10
25.5 18
35.5 25
45.5 30
55.4 3

i need to find Q1, Q2, Q3, D7 and P30

Answer 1

whats D7 ?

Answer 2

deciles

Answer 3

i have my exam tomorrow please help!

Answer 4

@amistre64

Answer 5

deciles are divisions by 10
percentiles division by 100
quartiles division by 4

etc ...

the process is the same in each case, just sub in the appropriate divider

Answer 6

\[1~k-cile=\frac{\#~elements}{k}\]
\[n^{th}~k-cile=n*\frac{\#~elements}{k}\]
and round or average as needed

Answer 7

for example:there are \(\sum f\) individual elements

\[Q1=\frac{\sum f}{4})\]

Answer 8

Q1= 90+1/4 = 22.75th term which means i have to take the 22 and 23 term?

Answer 9

\[Q3=3*\frac{\sum f}{4}\]

Answer 10

22.75 rnds up to 23

if we had gotten 22.0000 then we would average the 22 and 23 elements

Answer 11

and thats Q1 = 90/4, rounded not 90+1/4 :)

Answer 12

90/10 = 1D

9*7 = 63 so you would average the 63,64 elements ... but if they are the same value then thats a rather pointless step :)

Answer 13

i have seen in many website the formula for Q as i* n+1/4

Answer 14

Qk = k*n/4

Answer 15

youd have to link the sites for me to see what you are trying to express :)

Answer 16

ok wait

Answer 17

http://www.alcula.com/calculators/statistics/quartiles/

here you go

Answer 18

http://quartilesdecilespercentiles.blogspot.com/#

also this one

Answer 19

i see, they are starting their count at n=0 or n=1 and are adjusting for it

Answer 20

now which formula should i follow?

Answer 21

1 2 3 4 5 6

lets take this for example:

the median is equal to Q2 is 3.5

Q2 = 2*6/4 = 3 ... the average of 3+4 is 3.5

Answer 22

Q0 = 0*6/4 = 0 ... what is the 0th position? may be what they are trying to address

Answer 23

i don't get it. like even from that formula i could get 3.5

Answer 24

by their account: Q2 = the 2*7/4 ... out right so they seem to be combining the averaging step to a more concise form

Answer 25

they have to adjust when it is not an integer ... but im just used to the way i was taught it

Answer 26

the formula you use is the one your material gives you to work with. is the best advice i can give for that one

Answer 27

this problem may not make it so complicated ... since the like the 14th and 15th elements are the same value.

Answer 28

90/4 = Q1 = 22.xx, so the 23rd value

elements 15 thru 32 are all the same value

Answer 29

no it is not just about one question. i mean which one should use generally?

Answer 30

Q2 = 2*90/4 = 45


5.5 4 4
15.5 10 14
25.5 18 32
35.5 25 57 .... 45 is in these
45.5 30
55.4 3

Answer 31

generally i use the one i posted to start with

Answer 32

D7 = 7*90/10 = 70


5.5 4 4
15.5 10 14
25.5 18 32
35.5 25 57
45.5 30 87 70 is in this set ....
55.4 3

Answer 33

P30 = 30*90/100 = 27 which is in the third grouping regardless of interpolation

Answer 34

yeah i got it. but i am still confused about quartile formula. it is used in so many other formulas as well that i am afraid my answer will go wrong

Answer 35

forget the formula and look at what is going on in the process.

you are dividing the data set into Quart=4 parts and picking the 1,2,3,4 Q

Answer 36

how accurate you need to be is up to the person doing the grading and all sorts of interpolations can be generated to match the accuracy needed.

Answer 37

so either formula could be used?

Answer 38

yes, they are both expressing the same thing but differ on how accurate you want the outcome.

Answer 39

in this specific instance, the interpolation doesnt matter since some number between 25.5 and 25.5 is going to be 25.5

Answer 40

ok thank you so much and wish me luck for tomorrow's exam :)

Answer 41

good luck ;)

Answer 42

:)