CHARACTERISTICS OF NORMAL PROBABILITY CURVE

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.

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.

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%).

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.