Turn on thread page Beta

Simple explanations of how to do Spearman Rank & Standard Deviation Please? watch

    • Thread Starter
    Offline

    17
    ReputationRep:
    Just wondering if someone could explain how to do the Spearman Rank and Standard Deviation techniques in the simplest way possible?
    Offline

    0
    ReputationRep:
    Here's standard deviation:

    You start with a load of data like:
    34 45 56 23 79
    (If you don't, and you start with a frequency table or something, let me know because you have to do different stuff for that!)

    Square each number:
    1156 2025 3136 529 6241

    Now add all of the above together:
    13087

    And then divide how many there are:
    2617.4

    Moving on, now find the mean average of the original data (add them and divide by number of them):
    47.4

    Square it:
    2246.76

    Now take this number (2246.76) from the number we calculated before (2617.4) to get:
    370.64

    And finally, square root it:
    19.252 (to 5.s.f.)


    So:

    Square
    Add
    Divide by n

    Average of original data
    Square
    Take
    Root
    Omg i just found the standard deviation!

    Spoiler:
    Show
    If you can't remember which one to take from which on the "Take" step, then just think it's the one which gives a positive answer!
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by Lou Reed)
    They're both long-winded and boring to calculate, so no simple ways really.

    For SD, i remember it as "sum of x squared over n", that's not all you do, here are the steps for a frequency table;
    - square x to get x^2
    - times frequency by corresponding x^2
    - sum this
    - divide by n
    - minus the mean squared (i'm sure you know how to work out mean)
    - square root it

    For SR, the equation is really self-explanatory:



    - find differences between the data
    - square them
    - sum them
    - times by 6
    - divide answer by (n(n^2 - 1))
    - take answer away from 1

    Does that help?
    Seems to, just give me a bit to get my head round it lol.
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by placenta medicae talpae)
    Here's standard deviation:

    You start with a load of data like:
    34 45 56 23 79
    (If you don't, and you start with a frequency table or something, let me know because you have to do different stuff for that!)

    Square each number:
    1156 2025 3136 529 6241

    Now add all of the above together:
    13087

    And then divide how many there are:
    2617.4

    Remember this number!
    Write it down or something

    Moving on, now find the mean of the original data (add them and divide by number of them):
    47.4

    Square it:
    2246.76

    Now take this number (2246.76) from the number we calculated before (2617.4) to get:
    370.64

    And finally, square root it:
    19.252 (to 5.s.f.)
    Nice explanation

    How would I calculate it for data on a frequency table then?
    Offline

    0
    ReputationRep:
    (Original post by sandeep90)
    Seems to, just give me a bit to get my head round it lol.
    Oh, erm, about this one - it's important that it's the ranks which have to be considered, rather than the actual values!
    Offline

    0
    ReputationRep:
    (Original post by sandeep90)
    Nice explanation

    How would I calculate it for data on a frequency table then?
    Cheers - I edited it a bit, so it's much clearer now

    To be honest, the formula is pretty much the same:
    I just think of it as "stick an f before the x".

    So instead of being:
    \sigma = \sqrt{\frac{\sum x^2}{n}-\bar{x}^2}

    It is now:
    \sigma = \sqrt{\frac{\sum f x^2}{n}-\bar{x}^2}

    Spoiler:
    Show
    If you prefer the alternative formula, then instead of being:
    \sigma = \sqrt{\frac{\sum (x-\bar{x})^2}{n}}
    It is now:
    \sigma = \sqrt{\frac{\sum f(x-\bar{x})^2}{n}}


    And here, f.x^2 is the value representing a class, squared, and then timesed by the frequency of that class - how many values lie therein.
    I appreciate that might be a little vague; let me know if it needs to be clarified.

    I think that (surprisingly) the hardest bit of this is remembering how to find the mean from the frequency table!

    \bar{x}=\frac{\sum x}{n}
 
 
 

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.