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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

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