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Characteristics of normal probability curve

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Characteristics of normal probability curve

1. 1. CHARACTERISTICS OF NORMAL PROBABILITY CURVE
2. 2. INTRODUCTION  The literal meaning of the term normal is average.  We make use of this term while computing the average in data related to education , psychology or sociology.  In this area, those who are able to reach a particular fixed level of qualification or characteristics are termed as normal.  In simple terms by probability we mean the possibility of being selected.  NPC is mainly computed for finding out average strength of the class, average marks and its distribution.
3. 3. PROPERTIES OF NORMAL PROBABILITY CURVE  For this curve mean, median and mode are the same at the centre of the curve.  The curve is perfectly symmetrical.  Since there is only one maximum point in the curve, the normal curve is unimodal, i.e. it has only one mode.
4. 4. PROPERTIES OF NORMAL PROBABILITY CURVE  It extends from minus infinity to plus infinity.  As the curve doesn’t touch the baseline , the mean is used as the starting point for working with normal curve.  To find the deviation from the point of departure(i.e. mean), standard deviation of the distribution is used as a unit of measurement  There are two equal halves(50%-50%).
5. 5. PROPERTIES OF NORMAL PROBABILITY CURVE  The curve extends on both sides -3 sigma distance on the left to +3 sigma distance on the right.  The total area under the curve is equal to 1.  It is completely determined by its mean and standard deviation.  The Empirical Rule – About 68% of the area under the graph is within one standard deviation of the mean; about 95% of the area under the graph is within two standard deviations; 99.7% of the area under the graph is within three standard deviations of the mean.