MBA 604 Introduction Probaility and Statistics Lecture Notes
MBA 604 Introduction Probaility and Statistics Lecture Notes
MBA 604 Introduction Probaility and Statistics Lecture Notes
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5 Sample Mean <strong>and</strong> Variance<br />
For Grouped Data<br />
Example: (weight loss data)<br />
Let k = number of classes.<br />
Formulas.<br />
Weight Loss Data<br />
class boundaries mid-pt. freq. xf x2f x f<br />
1 5.0-9.0- 7 3 21 147<br />
2 9.0-13.0- 11 5 55 605<br />
3 13.0-17.0- 15 7 105 1,575<br />
4 17.0-21.0- 19 6 114 2,166<br />
5 21.0-25.0- 23 3 69 1,587<br />
6 25.0-29.0 27 1 27 729<br />
Totals 25 391 6,809<br />
<br />
xf<br />
xg =<br />
n<br />
s 2 2 2 x f − ( xf) /n<br />
g =<br />
n − 1<br />
where the summation is over the number of classes k.<br />
Exercise: Use the grouped data formulas to calculate the sample mean, sample variance<br />
<strong>and</strong> sample st<strong>and</strong>ard deviation of the grouped data in the weight loss example. Compare<br />
with the raw data results.<br />
6 z-score<br />
1. The sample z-score for a measurement x is<br />
z =<br />
x − x<br />
s<br />
2. The population z-score for a measurement x is<br />
17