Statistics 1 - Edexcel

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SKEWNESS

Negative Skew

mean < median < mode

  (Q2 – Q1) > (Q3 – Q2)

Longer left hand whisker

 Positive Skew

 mode < median < mean

    (Q2 – Q1) < (Q3 – Q2)

Longer right hand whisker

Symmetrical

mode = median = mean

  (Q2 – Q1) = (Q3 – Q2)

       Equal whiskers

Interpolation to find a median Value

Lower Class Boundary + (Cumulative Frequency X whatever you want to find, e.g. 0.25 for Q1, Minus the Cumulative Frequency before the modal class, Divide by Frequency in the modal class) Then Times by the Class Width.

Equation (http://www.allinfo.plus.com/levelup/Images/linear.gif)

Mean

(http://www.mathsisfun.com/data/images/mean-frequency-table.gif)  The mean is very simple to calculate, If you are given a table with single integers on the top, e.g. 1,2,3,4(x) , and they have frequencys to them, e.g. the number 1 has a frequency of 5 (f). all you do is make a new table and calculate all the X's multiplied by the Frequencys, this is FX, then Add them together to get the sum of FX, Efx. Then devide Efx by the sum of all the Frequencys, EF, which is also the same as CF.

However if the Data is in groups, e.g. 0-9. Then Instead of Summing Efx, You should Sum the Frequency multiplied by the Midpoints of the Grouped data. e.g. mp of 0-9 is 4.5. So its Ef(mp) over Ef in grouped data.

Variance and Standard Deviation.

Variance = Sum of X^2 / n (The number of data sets, not the total) - Xbar^2(the mean squared)                 or see below for when it involves frequency's

Variance = Sum of FX^2 over the Sum of F, - Xbar^2(The mean squared).

The Standard Deviation is simply the Square Root of the Variance.

Probability 

P(Event A or Event B) = P(AuB)

P(Both Events A and B) = P(AnB)    (Remember this one because it had N in the middle like AND)

P(Not Event A) =

Comments

Noor

Thank you! Exactly what I needed! :)

Harry Owen

No problem, im doing an absolute grind through before the exam, so im continually updating it mate lol :D

Noor

Thanks! Any more updates? :P

I think I am screwed for this exam.. :/

*Goes off to write the formulas down 8 times*

:)

forbidden

to remember the pmcc think of the **** song! sxy/by the square root of sxxsyy!! btw thanks for this!!

Lydia xo

this is really good! thanks!

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