1 / 11

Quantitative Methods

Quantitative Methods. Part 2 Standard Deviation. Standard Deviation. Measures the spread of scores within the data set Population standard deviation is used when you are only interested in your own data

nardo
Télécharger la présentation

Quantitative Methods

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quantitative Methods Part 2 Standard Deviation

  2. Standard Deviation • Measures the spread of scores within the data set • Population standard deviation is used when you are only interested in your own data • Sample standard deviation is used when you want to generalise for the rest of the population

  3. Standard Deviation • To find the standard deviation • Calculate the deviation from mean (x – m ) • Square this (x – m ) * (x – m ) • Add all squared deviation (S) = SS • SD ( s ) = Square Root of SS / N

  4. Standard Deviation

  5. Workshop 3 Activity 4 Comp1 and Comp 2 student grades: • Comp1: 12, 15, 11, 12, 13, 10, 12, 9, 15, 14, 12, 13 ,14, 11, 12, 13, 14, 11, 13, 11, 10, 12 • Comp2: 15, 15, 12, 15, 9, 15, 10, 9, 15, 15, 9, 14, 10, 9, 9, 15, 15, 9, 14, 10, 9, 15

  6. Workshop 3 Activity 4 • Calculate the deviation of each number from the mean, like this (data number – mean) (Look at Wk3Act4.xls) • Square each of these deviations (data number – mean)*(data number – mean) • Add up all these squared deviations. (SS) • Calculate the standard deviation as “the square root of (SS divided by N)” where N is the number of data points.

  7. How did I do in my OOP exam? • A student gets 76 out 100 • Sounds good, but is it?  • Depends on what the rest of the class got • Need to take the mean score into account • If mean score = 70 then it is 6 points better than average then  • But how did the rest of the class do? • Need to know the spread of grades round the mean • If lots got 10 points above then 

  8. Can Standard Deviation Help? • His raw score X = 76 • Mean m = 70 • SD s = 3 • We can see that the score is 2 sds above average (76 – 70)= 6 and 6/3 = 2 sds • 97.72% got 76 or below • Only 2.28 % did better

  9. Same Student, different module • His raw score X = 76 • Mean m = 70 • SD s = 12 • We can see that the score is only 1/2 sd above average (76 – 70)= 6 and 6/12 = ½ sd • 69.15% got 76 or below • But 30.85 % did better

  10. Z - Scores • Z = ×-μ/σ • A specific method for describing a specific location within a distribution • Used to determine precise location of an in individual score • Used to compare relative positions of 2 or more scores

  11. Workshop • Work on Workshop 5 activities • Your initial Gantt chart and Start on initial questions • Your journal (Homework) • Your Literature Review (Hand in) References • Dr C. Price’s notes 2010 • Gravetter, F. and Wallnau, L. (2003) Statistics for the Behavioral Sciences, New York: West Publishing Company

More Related