The frequency of a class is centred at its mid-point, called its class mark.

The cumulative frequency of a class is the frequency obtained by adding the frequencies of all the classes preceding the given class.

There is a empirical relationship between the three measures of central tendency : 3 Median = Mode + 2 Mean

The term ‘ogive’ is pronounced as ‘ojeev’ and is derived from the word ogee. An ogee is a shape consisting of a concave arc flowing into a convex arc, so forming an S-shaped curve with vertical ends. The median of grouped data can be obtained graphically as the x-coordinate of the point of intersection of the two ogives for this data.

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