1 / 17

STANDARD DEVIATION

RESEARCH METHODOLOGY

Download Presentation

STANDARD DEVIATION

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. STANDARD DEVIATION M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.

  2. It is an improvement over mean deviation • Measure of dispersion • Used most commonly in statistical analyses

  3. Calculation of SD • First find the mean of series • Find the deviation or difference of individual measurement from mean • Next find the sum of squares of deviation or difference of individual measurements from their mean • Now find the variance (Var) – mean squared deviation var = ∑ (X - X) 2/ n

  4. Square root of variance that gives SD • If large sample size : • If sample less than 30 :

  5. For ex : Mean = 2+5+3+4+1/5 = 15/5 = 3 Var = 10/5 = 2

  6. Uses of SD • It summarizes the deviation of a large distribution from mean in one figure used as unit of variation • Indicates whether the variation of difference of an individual from mean is by chance • Helps in finding the SE which determines whether the difference between means of two similar samples is by chance or real • Helps in finding the suitable size of sample for valid conclusion.

  7. SD of normal curve • The shape of curve will depend upon mean and SD of which in turn depend upon the number and nature of observation. • In normal curve :- • Area b/w 1 SD on either side of mean will include approximately 68% of values in distribution • Area b/w 2 SD is 95% • Area b/w 3 SD is 99.7% • These limits on either side of mean are called “confidence limits”

  8. Standard normal curve • Smooth • bell shaped • Perfectly symmetrical • Based on infinity large number of observation • Total area of curve = 1 • Mean = 0 • SD = 1 • Mean , median and mode all coincide

  9. Thank you

  10. SD of normal curve • Bell shaped curve will show an inflexion on the ascending as well as descending units of curve • If vertical lines are drawn from each of these points they will intersect the X axis on either side of the mean at an equal distance from it • A large portion of area under the normal curve has been included in portion of curve b/w the 2 points of inflexion

  11. The distance b/w the mean and point of inflexion either side is equal to SD and is denoted by a + sign prefixed to it to indicate that it extends on either side of mean. • If another vertical line is drawn an either side of mean at a distance equal to twice SD most of values in distribution table would have been included in this part of curve • In most cases, + SD will include 2/3 of sample values and mean + 2 SD will include 90% of values.

  12. THANK YOU

More Related