The information in the form of facts or figures is called data. Its singular form is called datum. The data collected by someone with a specific purpose in mind is called primary data. Data collected from some other source, which has been originally collected for some other context, is called secondary data. The process of gathering information is called collection of data. The way to present the collected data in an understandable and meaningful form is called presentation of data. The number of times an observation occurs is called frequency of that observation. In grouped frequency distribution table, the groups of observations made are called class intervals. The size of the class interval is called class size or class width. Grouped Frequency Distribution: While forming this frequency table, the observations are categorised into groups, with defined class interval and class size. When the upper limit is included to class interval while forming a frequency table, it is called the inclusive method. When the upper limit is not included to class interval while forming a frequency table, it is called the exclusive method. The collected data can be represented graphically using bar graphs, histograms and frequency polygons. The three measures of central tendency are mean, median and mode. • Mean: Mean of a number of observations is the sum of the values of all the observations divided by the total number of observations. It is denoted by . For ungrouped frequency distribution, • Median: Median is the middle most value of an observation. If n is odd, then the value of median If n is even, then the value of median • Mode: Mode is the most re-occurring term in an observation.

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