Which of the following denotes the trend of events that pass with time?
Ans. c (Line chart) (Ref. Text book of biostatistics by B K Mahajan, Vlth /pg. 20; Park PSm 22nd/788)Line diagrams are used to show the trend of events with the passage of time.Type of dataQualitative dataQuantitative dataDefinitionCharacteristics same, only frequency variesCharacteristics as well as frequency both varyExampie Method of presentation of dataMales, females1. Bar diagramLength of the bars, drawn vertical or horizontal, indicates the frequency of a character. Bar may be drawn in ascending or descending order of magnitude. Spacing between any two bars should be nearly equal to half of the width of the bar. There are four types of bar diagrams,a) Simple bar diagram:Here bars can be arranged vertically or horizontally. A suitable scale must be used to present the length of the bars.b) Multiple bar diagram:Here two or more bars are grouped together.c) Component bar diagram:The bars may be divided into two or more parts. Each part represents a certain item.d) Proportional bar diagram:Each bar represents 100%. The bars may be divided into two or more parts. Each part is proportional to the magnitude of that particular itemHeight, weight, blood pressure1. Histogram - To construct a histogram the class intervals are plotted along X axis (horizontal line) and corresponding frequencies (or no. of observations) on Y-axis (vertical line). Rectangles are constructed such that height of a rectangle is proportional to the frequency of class and width is equal to length of the class. If all classes are of equal length then all the rectangles will have equal width. Histogram is an area diagram.2. Pie diagramThe frequencies of the groups are shown in a circle. Degrees of angle denote the frequency and area of the sector. Size of each angle is calculated by the formula as: Angle (Degrees) = Class frequency X 360deg/Total observations2. Frequency polygon - It is an area diagram of frequency distribution developed over a histogram. Join the midpoints of class intervals at the height of frequencies by straight lines. It gives a polygon, i.e., figure with many angles.3. Pictogram -- It is a popular method of presenting data to the layman. Here each picture indicates a unit of characteristic. These charts can be used for illiterate persons. Because of its attractive presentation it can be utilized for the man on the street.3. Frequency curve - when the no. of observations is very large and group intervals are reduced, the frequency polygon tends to lose angulations giving place to a smooth curve known as frequency curve.4. Spot map - These maps are prepared to show geographical distribution of frequencies of characteristic4. Line chart - This is a frequency polygon presenting variations by line. It shows the trend of an event occurring over a period of time-rising, falling or showing fluctuations. Cumulative frequency curve (Ogive) - Successive class frequencies are added and a frequency polygon is drawn. Number or percent of observations falling below or above a specific value can be presented in this graph. Any point below which there are certain percent of observations is called as percentile and graph drawn out of such points is a 'percentile graph'.5. Scatter (Correlation) diagram: It is graphic representation made to show the nature of correlation between two variable characters X and Y in the same person(s) or group(s) such as height and weight in men aged 20 years, hence it is also called correlation diagram. The characters are read on the base (X-axis) and vertical (Y-axis) and the perpendiculars drawn from these readings meet to give one scatter point. Varying frequencies of the characters give a number of such points or dots that show a scatter. A line is drawn to show the nature of correlation at a glance.
Frequency polygon
Histogram
Line chart
Pie diagram
Biostatistics