biostatstics :Type and presentation of data

PG Guide: Dr S.R. Suryawanshi PG Student: Dr Naresh Gill Type and Presentation of Data

Data: A set of values recorded on one or more observational units i.e. Object, person etc Types of data: Qualitative/ Quantitative data Discrete/ Continuous data Primary/ Secondary data Nominal/ Ordinal data

Qualitative data : also called as enumeration data . Represents a particular quality or attribute. There is no notion of magnitude or size of the characteristic, as they can't be measured. Expressed as numbers without unit of measurements . Eg: religion, Sex, Blood group etc. Quantitative data: Also called as measurement data. These data have a magnitude. Can be expressed as number with or without unit of measurement. Eg: Height in cm, Hb in gm%, BP in mm of Hg, Weight in kg.

Discrete / Continuous data : Discrete data: Here we always get a whole number. Eg. Number of beds in hospital, Malaria cases . Continuous data : it can take any value possible to measure or possibility of getting fractions. Eg. Hb level, Ht, Wt. Quantitative data Qualitative data Hb level in gm% Anemic or non anemic Ht in cms Tall or short BP in mm of Hg Hypo, normo or hypertensive IQ scores Idiot, genius or normal

Primary/ Secondary data : Primary data : Obtained directly from an individual , it gives precise information . Secondary data : Obtained from outside source ,Eg: Data obtained from hospital records, Census. Nominal/ Ordinal data : Nominal data: the information or data fits into one of the categories, but the categories cannot be ordered one above another . E.g. Colour of eyes, Race, Sex. Ordinal data: here the categories can be ordered, but the space or class interval between two categories may not be the same. E.g.. Ranking in the class or exam

Collection of data Collect data carefully and thoroughly. Units of measurements should be clearly defined. Record should be correct , complete, clear, sufficiently concise and arranged in a manner that is easy to comprehend. Collected data should be Accurate (i.e. Measures true value of what is under study) Valid ( i.e. Measures only what is supposed to measure) Precise (i.e. Gives adequate details of the measurement) Reliable (i.e. Should be dependable)

Sources for collection of data Census: The First regular census in India was taken in 1881, taken every 10 years. Defined as “The total process of collecting, compiling and publishing demographic, economic and social data pertaining at a specific time or times, to all persons in a country or delimited territory.”. Registration of vital events : Civil registration System. In 1873,GOI passed the Births, Deaths and Marriages Registration Act, but the Act provided only for voluntary registration. However the registration system in India tended to be very unreliable, the data being grossly deficient in regard to accuracy, timeliness, completeness and coverage.

Continued.. The Central Births and Deaths Registration Act, was passed by Govt Of India in 1969, but it came into force on 1 st April 1970.The acts provides the compulsory registration of births and deaths throughout the country, and compilation of vital statistics in the states to so as to ensure uniformity and comparability of data. Time limit: For events of births-21 days, and for events of deaths-21 days. In case of default fine up to Rs 50 can be imposed. Sample Registration System(SRS): Dual record system, consisting of continuous enumeration of births and deaths by an enumerator and independent survey every 6 months by an investigator-supervisor.

Notification of diseases: Valuable source of morbidity data such as incidence, prevalence and distribution of certain specified diseases which are notifiable. Internationally notifiable diseases: Cholera, Plague and Yellow fever. A few others- Louse-borne typhus, Relapsing fever, Polio, Influenza, Malaria, Rabies and Salmonellosis are subject to international surveillance. Hospital Records: Primary and basic source of information about disease prevalent in the community . Serious limitation of this data is that it represents only those individuals who seek medical care and we do not know denominator due to lack of precise boundaries of catchment area of hospital.

Epidemiological Surveillance: Special surveillance activities are conducted for diseases like Malaria, Leprosy, TB, Filariasis, AIDS etc. Surveys: Population surveys supplement routinely collected statistics . Methods used in data collection in surveys include health interview, health examination, study of health records, mailed questionnaire survey. Research Findings: Findings of various research or investigations are helpful for planning and implementation of health activities in general.

Presentation of data Principles of presentation of data: Data should be arranged in such a way that it will arouse interest in reader. The data should be made sufficiently concise without losing important details. The data should presented in simple form to enable the reader to form quick impressions and to draw some conclusion, directly or indirectly. Should facilitate further statistical analysis . It should define the problem and suggest its solution.

Methods of presentation of data The first step in statistical analysis is to present data in an easy way to be understood. The two basic ways for data presentation are Tabulation Charts and diagram

Rules and guidelines for tabular presentation Table must be numbered Brief and self explanatory title must be given to each table. The heading of columns and rows must be clear, sufficient, concise and fully defined. The data must be presented according to size of importance, chronologically, alphabetically or geographically If data includes rate or proportion, mention the denominator. Table should not be too large. Figures needing comparison should be placed as close as possible.

Continued.. The classes should be fully defined, should not lead to any ambiguity. The classes should be exhaustive i.e. should include all the given values. The classes should be mutually exclusive and non overlapping. The classes should be of equal width or class interval should be same Open ended classes should be avoided as far as possible. The number of classes should be neither too large nor too small. Can be 10-20 classes. Formula for number of classes(K): K=1+3.322 log 10 N , where N is total frequency

Tabulation Can be Simple or Complex depending upon the number of measurements of single set or multiple sets of items. Simple table : Title: Numbers of cases of various diseases in Nair hospital in 2009 Disease Cases Malaria 1100 Acute GE 248 Leptospirosis 60 Dengue 100 Total 1308

Frequency distribution table with qualitative data: Title: Cases of malaria in adults and children in the months of June and July 2010 in Nair Hospital. Jun-10 Jul-10 Type of malaria Adult Child Adult Child Total P.Vivax 54 9 136 23 222 P.Falciparum 11 0 80 13 104 Mixed malaria 11 4 36 12 63 Total 76 13 225 43 389

Frequency distribution table with quantitative data: Fasting blood glucose level in diabetics at the time of diagnosis Fasting glucose level No of diabetics Male Female Total 120-129 8 4 12 130-139 4 4 8 140-149 6 4 10 150-159 5 5 10 160-169 9 6 15 170-179 9 9 18 180-189 3 2 5 44 34 78

Chart and diagram Graphic presentations used to illustrate and clarify information. Tables are essential in presentation of scientific data and diagrams are complementary to summarize these tables in an easy, attractive and simple way.

The diagram should be: Simple Easy to understand Save a lot of words Self explanatory Has a clear title indicating its content Fully labeled The y axis (vertical) is usually used for frequency

Various charts and diagrams Bar Diagram Histogram Frequency polygon Cumulative frequency curve Scatter diagram Line diagram Pie diagram

Bar diagram Widely used, easy to prepare tool for comparing categories of mutually exclusive discrete data. Different categories are indicated on one axis and frequency of data in each category on another axis. Length of the bar indicate the magnitude of the frequency of the character to be compared. Spacing between the various bar should be equal to half of the width of the bar. 3 types of bar diagram: Simple Multiple or compound Component or proportional

Multiple bar chart : Each observation has more than one value, represented by a group of bars. Percentage of males and females in different countries, percentage of deaths from heart diseases in old and young age, mode of delivery (cesarean or vaginal) in different female age groups .

Component bar chart : subdivision of a single bar to indicate the composition of the total divided into sections according to their relative proportion. For example two communities are compared in their proportion of energy obtained from various food stuff, each bar represents energy intake by one community, the height of the bar is 100, it is divided horizontally into 3 components (Protein, Fat and carbohydrate) of diet, each component is represented by different color or shape .

Component or proportional bar diagram

Histogram: It is very similar to the bar chart with the difference that the rectangles or bars are adherent (without gaps). It is used for presenting class frequency table (continuous data). Each bar represents a class and its height represents the frequency (number of cases), its width represent the class interval.

Frequency Polygon Derived from a histogram by connecting the mid points of the tops of the rectangles in the histogram. The line connecting the centers of histogram rectangles is called frequency polygon. We can draw polygon without rectangles so we will get simpler form of line graph. A special type of frequency polygon is the Normal Distribution Curve.

Cumulative frequency diagram or O’give Here the frequency of data in each category represents the sum of data from the category and the preceding categories. Cumulative frequencies are plotted opposite the group limits of the variable. These points are joined by smooth free hand curve to get a cumulative frequency diagram or Ogive.

Scatter/ dot diagram Also called as Correlation diagram ,it is useful to represent the relationship between two numeric measurements, each observation being represented by a point corresponding to its value on each axis. In negative correlation, the points will be scattered in downward direction, meaning that the relation between the two studied measurements is controversial i.e. if one measure increases the other decreases While in positive correlation, the points will be scattered in upward direction.

Line diagram : It is diagram showing the relationship between two numeric variables (as the scatter) but the points are joined together to form a line (either broken line or smooth curve. Used to show the trend of events with the passage of time.

Pie diagram: Consist of a circle whose area represents the total frequency (100%) which is divided into segments. Each segment represents a proportional composition of the total frequency.

biostatstics :Type and presentation of data

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