Chapter 20

Card Set Information

Author:
damea134
ID:
306338
Filename:
Chapter 20
Updated:
2015-08-13 02:22:13
Tags:
Chance Error
Folders:
Statistics
Description:
Chance error in sampling
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user damea134 on FreezingBlue Flashcards. What would you like to do?


  1. Find the Expected Value
    How to find expected value in a sample of 25000 people

    • 10000 republicans 
    • 15000 democrats

    Sample size = 100

    Find the EV of republicans (not box)

    To find the expected value you have to find the average of the box

    • EV = (Number of draw x average of box)
    • Solution:

    ave of republicans = 10000/25000 =.04

    EV = 100 (#draws) x .04 (Ave) = 40
  2. Find the SD 
    Using SD ShortCut (289)
    Formula:

    Big# - Small# x [Square Root of (fraction of Big#) x (fraction of Small#)]

    • Can only be used with two numbers
    • 5,1,1,1

    Example

    (5-1) x 

    example 1,0

    • 25000
    • 10000 republicans
    • 15000 democrats

    1s, 0s

    SD = (1-0) x [Square root of (10000/25000 x 15000/25000)] = 4.9
  3. Finding the SE for Precentage
    SE for Precentage = SE of sample/#Draws) x 100

    How to find expected value in a sample of 25000 people

    • 10000 republicans 
    • 15000 democrats
    • Sample/draws = 100

    SE for Number (Republicans)

    • Find SD = 4.9 (or about 5)
    • SE = 10 x .5 = 5
    •  
    • Now use percentage formula

    (.5/100) x 100% = 5%
  4. Using Box Model
    If there are more than 2 numbers use box model to Consisting of 1 & 0

    example:

    out of a 100000 samples

    • 20% have shoes
    • 50% are broke
    • 40% have bad credit
    • 10% are on crack  

    Draws =1000

    Isolate the Variable it ask for into 1s & 0s

    find expected value (EV) of people who have bad credit 40% or 40,000

    find the SE  (need SD... this is where the box model shines)

    40% bad credit and the 60% good credit

    SD = Square Root of (.4 x .6) = .49

    SE = Square Root of (1000draws) x (.49 SD)

    SE = 15
  5. Using the Normal Curve
    out of a 100000 samples

    • 20% have shoes
    • 50% are broke
    • 40% have bad credit
    • 10% are on crack  
    • Draws =1000

    Find percentage between 39% and 40% have bad credit

    Need to convert into standard units

    • EV = 40%
    • SE = 15
    • Convert to percent 15/1000 = 1.5%

    • 39-40 = 1, 1/1.5 = +/- .67
    • Now look a normal curve to find percentage
    • Answer = 48%

What would you like to do?

Home > Flashcards > Print Preview