Epidemiology Finals PDF

**TYPES OF EPIDEMIOLOGICAL INVESTIGATIONS** **DESCRIPTIVE EPIDEMIOLOGY**: It involves observing and recording diseases and possible causal factors. It is usually the first part of an investigation. **ANALYTIC EPIDEMIOLOGY:** The objective is to test a hypothesis (statement about the relationship o...

**TYPES OF EPIDEMIOLOGICAL INVESTIGATIONS** **DESCRIPTIVE EPIDEMIOLOGY**: It involves observing and recording diseases and possible causal factors. It is usually the first part of an investigation. **ANALYTIC EPIDEMIOLOGY:** The objective is to test a hypothesis (statement about the relationship of two variables). The goal is to approximate as best as possible the counterfactual state of the world (using identical individuals or comparison groups). **Analytic epidemiology is classified in several ways:** a. **Observational or Experimental:** presence of manipulation of the exposure variable. b. **Prospective, Retrospective:** direction of inquiry on the presence of exposure and disease. c. **Longitudinal or Cross-Sectional:** whether or not the assessment of the factor and the outcome relate to two time points in the life study of the participant. **THEORETICAL EPIDEMIOLOGY:** consists of the representation of disease using mathematical 'models' that attempst to simulate natural patterns of disease occurrence. **EPIDEMIOLOGICAL SUBDISCIPLINES** - **Ecological Epidemiology (Medical Ecology):** focuses on understanding factors that affect transmission and maintenance of disease agents in the environment. - **Clinical Epidemiology:** use of epidemiological principles, methods and findings in the care of individuals, with particular reference to diagnosis and prognosis. - **Computational epidemiology:** it involves the application of computer science to epidemiological studies. It includes the representation of disease by mathematical models and the use of expert systems. - **Genetic epidemiology:** the study of the cause, distribution, and control of disease in related individuals, and of inherited defects in populations. - **Molecular epidemiology:** application of new diagnostic techniques in the study of disease. - **Others** a. **Chronic disease epidemiology**: involved with diseases of long duration (e.g. cancer, TB). b. **Environmental epidemiology**: concerned with the relationship between disease and environmental factors (e.g. pollution, occupational hazard). c. **Micro-epidemiology**: study of disease in a small group of individuals with respect to factors that influence its occurrence in larger segments of the population. It frequently uses animal biological models of disease, closely related to comparative epidemiology. d. **Macro-epidemiology:** study of national patterns of disease, and the social, economic and political factors that influence them. e. **Nutritional epidemiology** f. **Subclinical epidemiology** **COMPONENTS OF EPIDEMIOLOGY** A. **QUALITATIVE INVESTIGATIONS** - **Natural history of disease:** The ecology of diseases, including the distribution, mode of transmission and maintenance of infectious diseases, is investigated by field observation. - **Causal hypothesis testing:** If field observations suggest that certain factors may be associated with a disease, then the association must be assessed by formulating a causal hypothesis. B. **QUANTITATIVE INVESTIGATIONS** **SURVEYS:** examination of an aggregate of units. A group of animals is an example of an aggregate. : Surveys can be taken on a sample of the population. Less commonly, a census, which examines the total population, can be undertaken. - **CROSS-SECTIONAL SURVEY** records events occurring at a particular point in time. - **LONGITUDINAL SURVEY** records events over a period of time. - **Screening:** type of diagnostic survey, identification of undiagnosed cases of disease using rapid tests or examinations. **MONITORING AND SURVEILLANCE** - **Monitoring -** is the making of routine observations on health, productivity and environmental factors and the recording and transmission of these observations (e.g. regular recording of milk yield in a dairy farm). - **Surveillance** is a more intensive form of data recording than monitoring. Originally, surveillance was used to describe the tracing of people who were in contact with cases of infectious disease. It is now used in a much wider sense to include all types of disease (infectious and noninfectious). **STUDY** - **Descriptive study:** describing the distribution and frequency of a disease in a population in terms of animal, place and time. - **Experimental study (Intervention study):** the investigator has the ability to allocate animals to various groups, according to factors which the investigator can randomly assign to animals (e.g. treatment regimen, preventive techniques). **Examples: field trial and clinical trial.** - **Observational study** **Cross-sectional study:** investigates relationships between disease (or other health-related factors) and hypothesized causal factors (HCF) in a specified population. **Case-control study:** compares a group of diseased animals with a group of healthy animals with respect to exposure to HCF. **Cohort study:** a group exposed to factors is compared with a group not exposed to the factors with respect to the development of a disease. **MODELLING**: Disease dynamic and the effects of different control strategies can be represented using mathematical equations. **DISEASE CONTROL**: goal of epidemiology is to improve the veterinarian's knowledge so that diseases can be controlled effectively, and productivity thereby optimized. This can be fulfilled by treatment, prevention or eradication. **ANALYTIC EPIDEMIOLOGY -- OBSERVATIONAL STUDIES** **ANALYTICAL EPIDEMIOLOGY:** a. **Cohort Study-** a group of animals exposed and unexposed to hypothesized risk factor are selected and observed to record development of disease in each group. b. **Case-Control Study**-- group of diseased and non-diseased animals are compared with respect to presence of hypothesized risk factors. c. **Cross-sectional Study --** determine the simultaneous presence or absence of disease and hypothesized risk factor then prevalence is therefore recorded. **COHORT STUDY** **Classification:** - Analytic - Observational - Prospective - Longitudinal - Exposure-based **Study population:** Exposed group and Unexposed group (both free of disease of interest) **Objective:** To show that the probability of disease is ↑ in Exposed group than in Unexposed group **Subjects:** - **Cohort**: group of animals who share the same characteristics - **Closed fixed cohort**: fixed group followed up from a certain point in time until a defined endpoint w/o losses to follow up. - **Open or dynamic cohort:** persons enter or leave the study anytime; changing exposures; **Types of Cohort Designs:** a. **Prospective cohort:** Study participants are free of disease, and at risk of developing the disease b. **Retrospective cohort:** Individuals who are free of the disease/outcome of interest at some point in the past are identify and classified according to exposure levels. **Sources of Data on Exposure** - Records: medical, employment, registries, etc - Query of subjects themselves: interviews, self-administered question - Observation -- direct physical/lab exam - Proxy measurements: job title, distance from the source - Direct measurement of the environment - Surveillance of obituaries and death certificate - Periodic exam of the participants - Records -- clinic, hospital, employment, etc. **Steps in Cohort Study:** A. State d hypothesis in clear and specific terms Null hypothesis (Ho) refers to a general statement or default position that there is no relationship between two measured phenomena. Alternative hypothesis (Ha) maintained hypothesis or research hypothesis. B. Define d study variables operationally Exposure: living in a household w/ an adult who was diagnosed to be sputum positive for PTB Outcome: PTB diagnosed based on WHO guidelines C. Define d study population D. Identify and select d exposed group E. Identify and select d unexposed group F. Collect data at end of follow up G. Construct a 2x2 table **Diseased animals** **Non-disease animals** **Total** ----------------- ---------------------- ------------------------- --------------- **HCF present** **a** **b** **a+b** **HCF absent** **c** **d** **c+d** **Total** **a+c** **b+d** **a+b+c+d=n** H. Compute for the incidence of disease - **Incidence Proportion:** a/(a+b) - **Incidence Proportion:** c/(c+d) - **Incidence Proportion**: 100/150 = 0.6667 or 66.67% - **Incidence Proportion:** 50/150 =9.3833 or 38.33 % I. Compute for the risk ratio and interpret - **Risk Ratio (RR)** = (a/(a+b)) / (c/(c+d) - **Risk Ratio** = 0.6667/0.3833 = 1.74 - **Interpretation:** Those exposed (children living with PTB sputum + adult) have 1.74 more likely to develop PTB compared to the unexposed (not living with PTB + adult). **CROSS-SECTIONAL STUDY (aka "prevalence study")** A study to estimate d distribution of a quantity of interest or joint distribution of several quantities in a target pop at a certain moment in time. **Characteristics:** - Exposure status and disease status are measured at one point in time or over a very short period of time. - Prevalence rates among those w/ and w/o d exposure are determined and compared - Can measure attitudes, beliefs, behaviors, personal or family history, genetic factors, existing or past conditions, or anything else that does not require follow-up to assess **Uses:** Determine the association between outcome variable and some explanatory variables (e.g. obesity and hypertension). **FORMULA: Cross-Sectional Study** - Prevalence Proportion = a/(a+b) - Prevalence Proportion = c/(c+d) - Prevalence Ratio = (a/(a+b))/(c/(c+d)) **Prevalence Difference** PD = (PP in exposed) -- (PP in unexposed) = 0.66 -- 0.1 = 0.56 **Interpretation:** there are 56/100 more cases of asthma among subjects' w/ history of indoor cooking compared to those w/o history of indoor cooking. **CASE-CONTROL STUDY** **Classification:** Analytic, Observational, Retrospective, Longitudinal, Disease status-based **Study population:** Cases and Non-cases (compare proportion of exposed, factor) **Objective:** To show that the probability of exposure is ↑ in cases than in non-cases **Types of cases:** - Prevalent cases - Incident cases - Adv. of incident cases: - Uniform diagnosis - Accurate recall of events - Temporal sequence - Non-survivors **Definition and Selection of Controls** - **Define control group** -- comparable to d source pop of d cases. - **Select controls** -- get controls from d same source pop as d cases. **Measure of Association** **Odds Ratio:** The ratio of probability of an event occuring to the probability of it not occuring. **FORMULA:** Odds ratio = (a/c) / (b/d)  **Exposure odds smokers:** a/c = 100/100 = 1 **Exposure odds non-smokers:** b/d = 50/200 = 0.25 **Odds Ratio** = 1/0.25 = 4 **Interpretation:** the estimated risk of lung cancer is 4x more for those who have are smokers than those who are non-smokers. **NATURE & SOURCES OF VARIABLES AND DATA** **VARIABLE:** is any quality, characteristic or constituent of an individual or thing that can be measured. It is a phenomenon whose values or categories cannot be predicted with certainty, because it is subject to change. **EXAMPLES:** - Disease - Causal factors **Study variable --** any variable that is being considered in the investigation. **Response variable --** a variable that is affected by another variable called **'explanatory variable'.** **EPIDEMIOLOGICAL STUDIES:** disease is often the response variable, and the hypothesized causal factor (HCF) is the explanatory variable. **DATA:** the epidemiologist investigates the frequency and distribution of disease in groups of animals. This involves the collection and analysis of data (singular: datum), facts, especially numerical facts, collected together for reference or information. **CLASSIFICATION of DATA** - **QUALITATIVE DATA --** describe a property of an animal, that is, its membership to a group or class. Such data are therefore categorical. **Examples: breed, sex.** - **QUANTITATIVE DATA --** relate to amounts, rather than just indicating classes. **Examples are prevalence, incidence, body weight, milk yield, temperature and antibody titer.** **Quantitative data may be further divided into:** a. **Discrete --** can only have one of a specified set of values, such as whole numbers, for example, the number of teats on a sow. Discrete data generate counts. b. **Continuous --** may have one value within a defined range (though the range can be infinite). Continuous data are quantified by comparison with a fixed unit, that is, they are measured. **THERE ARE FOUR MAIN SCALES (LEVELS) OF MEASUREMENT:** - Nominal - Ordinal - Interval - Ratio **Nominal (Classificatory) Scale:** Involves the use of numbers (or other symbols) to classify objects. - This scale is a **'weak' form of 'measurement'.** **Ordinal (Ranking) Scale:** allows groups to be related to other groups. - Most commonly, the relation can be expressed in terms of equal to, greater than or less than. - The difference between the nominal and the ordinal scale is that the ordinal includes not only equivalence but also **'greater than' and 'less than' property.** **Interval Scale:** in an interval scale, the distance between the ranked values is known with some accuracy. - **Two thermal interval scales are commonly used:** Celsius and Fahrenheit - The interval scale is a relatively **'strong' form of (actual) measurement.** **Ratio Scale:** is an interval with a true zero point. - Note that a ratio scale is not necessarily associated with ratios, many of which are ratios of counts (e.g., prevalence). **Visual Analogue Scale:** the visual analogue scale (VAS) uses a straight line, usually 100 mm long, the extreme limits of which are marked with perpendicular lines. - The VAS is **commonly used in human medicine to assess pain** and has been **similarly applied in veterinary medicine.** **ELEMENTS OF DATA** **Diseases are defined at three levels:** - specific causes, - lesions or deranged functions, - presenting problems **Nomenclature and Classification of Disease** **Diseases** are generally named according to their allocation to one of these three levels; for example, parvovirus infection (specific cause), hepatitis (lesion), and ataxia (presenting problem). **Eponyms:** A fourth method of naming a disease. For example Rubarth's disease, Newcastle disease. - Veterinarians usually define and record disease as a diagnosis in terms of a combination of two or three of all the levels. **Disease can be diagnosed using one or more of four criteria:** - clinical signs and symptoms, - detection of specific agents, - reactions to diagnostic tests, - identification of lesions. **SENSITIVITY:** a diagnostic method is the proportion of true positives that are detected by the method. **SPECIFICITY**: a method is the proportion of true negatives that are detected. **Sensitivity:** proportion of true positives. **FORMULA:** - 35 / 145 = 0.24 or 24% - 530/572 = 0.93 or 93% **These terms can be used in relation to qualitative data and to quantitative measures:** - **ACCURACY** - is an indication of the extent to which an investigation or measurement conforms to the truth. - **REFINEMENT -** is the degree of detail in a datum. - **PRECISION** - can be used in two senses. First, it can be used as a synonym for refinement. Secondly, it can be used statistically to indicate the consistency of a series of measurements. - **RELIABILITY** - defined in terms of the degree of agreement between sets of observations made on the same animals by the same observer. - **VALIDITY** - is a long-term characteristic, of which sensitivity and specificity are indicators. The validity of a technique depends upon the disease that is being investigated and the method of diagnosis. **BIAS:** is any systematic (as opposed to random) error in the design, conduct or analysis of a study that renders results invalid. Bias is a long-run effect. Bias can be corrected if its extent is known. **Types of Bias:** - **Bias due to confounding/extraneous variable** - **Interview bias -** where an interviewer's opinions may affect accurate reporting of data - **Measurement bias** -- inaccurate measurement or misclassification of animals as diseased and non-diseased. - **Selection bias** - where animals selected for study have systematically different characteristics from those that are not selected for study. **CONFOUNDING (Latin: confundere = to mix together)** is the effect of an extraneous variable that can wholly or partly account for an apparent association between variables. Confounding can produce a spurious association between variables, or mask a real association. **REPRESENTATION OF DATA: CODING** **CODING**: a means of representing text and numerals in a standardized, usually abbreviated (shorthand) form. Such standardization enables veterinary and medical data to be recorded in a consistent, unambiguous and uniform way. **Code Structure** **Data about animals can be divided into two groups:** - Permanent data ("tombstone data") - Varying data ("descriptors" or "specifier types"). **AXIS:** data that define disease can comprise a single component. Alternatively, the definition can be broken down into constituent parts. **ALPHA CODES:** alpha codes represent text by alphabetical abbreviations or acronyms, for example: female = F, male = M. **ALPHANUMERIC CODES:** these codes have evolved more recently than numeric codes. A combination of letters and numbers are used. **SYMBOLS:** symbols can be used as codes. **Choosing a Code:** The choice of a code is partly subjective. Some people find numbers easier to handle; others are more content with letters. **NUMERIC CODES:** can be entered into computers more quickly than alpha codes. Numeric codes are not subject to language differences. **Error Detection**: This is important when combining data from different sources and when combining data that have satisfied different, perhaps incompatible sets of criteria. **Consistency:** initially, checks should be made that the codes are recognizable, and then that they are internally consistent. **Finger trouble:** Data that are entered via keyboards are subject to **four types of error:** - **Insertion** -- extra characters are added, - **Deletion** -- characters are omitted, - **Substitutions** -- wrong character is typed, and - **Transposition** -- correct characters are typed in the wrong order. **GENERAL CONSIDERATIONS ON DATA COLLECTION** **Nature of Data:** data from some sources may be unsuitable because they are inaccurate. Also, they may be of the wrong type. **Cooperation:** Cooperation is unlikely if data collection is laborious or time-consuming, if there is a risk for breach of confidentiality, and if the study is undertaken in isolation or not part of a planned animal health program. **Trace back:** data on the geographical distribution of disease may be difficult to gather because of an inability to trace animals back to their origin. **Bias:** sources may be biased, e.g. due to selection bias. **Cost of data collection:** In most countries, collection of information on diseases of national importance is supported by government funds. Lack of funds can restrict data collection. **Problems unique to developing countries:** - Poor laboratory diagnostic support, - Insufficient manpower, - Difficult terrain and transportation. **SOURCES OF VETERINARY EPIDEMIOLOGICAL DATA** **PRIMARY DATA:** are those obtained first hand by the investigator to help him answer specifically the purposes of his study; these data include those derived by observations (direct measurement) and query (interview or questionnaire). **SECONDARY DATA**: are those which are already existing and which have been obtained by some other people for purposes not necessarily those of the investigators. - Secondary data are more problematic since the user does not have control over how it was collected, the objectives behind the data collection and the definitions used in classifying individuals into the different categories of the variables considered. **Sources of Veterinary Epidemiological Data:** - **Government veterinary organizations:** DA-BAI (Dept. of Agriculture-Bureaue of Animal Industry) BAS (Bureau of Agricultural Statistics) NMIS (National Meat Inspection Service) - **Veterinary practitioners -- farm vets, small animal clinic vets;** PCPP (Phil. College of Poultry Practitioners) PCSP (Phil. College of Swine Practitioners), etc - Abattoirs -- public and private abattoirs/slaughterhouses - Poultry packing plants - Knacker yards - Serum banks - Registries - Pharmaceutical and agricultural sales -- PVDA (Phil. Veterinary Drug Asso.) - Zoological gardens -- Manila Zoo, Avalon Zoo, etc. **DIAGNOSTIC TESTING** **GLOSSARY** **Screening -**the application of a test to apparently healthy animals to detect infection or subclinical disease. **Serological Epidemiology** -the investigation of disease and infection in populations by the measurement of variables present in serum, e.g. antibodies, antigens, hormones, enzymes, minerals, and trace elements. **Methods of Diagnosing Infectious Diseases:** A. **Evidence of current infection** 1. Isolation of agent 2. Identification of agent's genes (molecular epidem.) 3. Clinical signs 4. Pathognomonic changes 5. Biochemical changes 6. Demonstration of an immune response: Ag, Ab detection (serological epidem.) B. **Evidence of past infection** 1. Clinical history 2. Pathognomonic changes 3. Demonstration of an immune response: Ab detection **Assaying Antibodies**: concentration of antibody is expressed as **[titer].** This is the highest dilution of serum that produces a test reaction. - **Seropositive**: animals with detectable antibody titers - **Seronegative**: animals with no detectable antibodies - **Seroconverted**: animals previously seronegative and now seropositive **Quantal Assay:** measures an ['all-or-none' response]; for example, agglutination or no agglutination, infected or non-infected. **Two systems are currently used:** - Single serial dilution assay - Multiple serial dilution assay **INTERPRETING SEROLOGICAL TESTS**: a 2 x 2 table displaying the relationship between two factors, one the test results, the other the actual disease status. **Diagnostic Tests**: are often used as means of establishing the prevalence of disease. - Apparent prevalence = (a + b) ÷ n - True prevalence = (a + c) ÷ n **TRUE POSITIVE** result derives from actual infection. **TRUE NEGATIVE** result indicates absence of infection. **False positive**: reactions occur for a variety of reasons. **Group cross-reactions:** can occur between an infectious agent and antibodies to different organisms with similar antigens. **Non-specific agglutinins:** mimic the effects of antibodies that are agglutinins. **FALSE NEGATIVE RESULT ALSO OCCUR DUE TO SEVERAL REASONS:** - Some animals show **[natural or induced tolerance to antigens]** and therefore do not produce antibodies when challenged with the agent - Improper timing may result in a test's failure to detect infection. - A serological test may be too insensitive to detect Ab. **Calculations for Evaluation of Diagnostic Tests:** a. **Sensitivity:** a/ (a + c) - proportion of the animals with the disease which test positive (a) - ability to correctly identify diseased animals - indication of how many false negative results can be expected a. **Specificity:** d/ (b+d) - Proportion of the animals without the disease which test negative (d) - Ability to correctly identify non-diseased animals - Indication of how many false positive results can be expected b. **Positive Predictive Value:** a/ (a+b) - The probability that the disease is present in an animal that tests positive c. **Negative Predictive Value** - The probability that the disease is absent in an animal that tests negative d. **False Negative Rate:** a / (a + c) e. **False Positive Rate:** b / (b + d) - Improper timing may result in a test's failure to detect infection. **MULTIPLE TESTING** **Parallel testing** involves conducting two or more tests on animals at the same time, and animals are affected if they are positive to any of the tests. **Serial testing:** tests are conducted sequentially (i.e. consecutively), based on the results of a previous test. Conventionally, only those animals that are positive to an initial test are tested again; therefore, only animals that are positive to all tests are affected. **Negative-herd retesting:** at herd level, testing can be conducted only on animals that are negative to an initial test. **Selecting the Most Appropriate Diagnostic Test:** - **Sensitive test** (One that is usually positive when disease is present) should be used: - When there is an important penalty for missing a disease - During the early stages of a diagnostic work-up (as a 'rule-out' test) - When screening for disease in a population where the prevalence is relatively low - **Specific test** (one that is rarely positive in the absence of disease) should be used to confirm ('rule-in') a diagnosis that has been suggested from other information. Specific test is **[particularly useful if the test result is positive.]** Calculation of sensitivity and specificity requires an independent, valid criterion -- also termed a **'gold standard'** -- by which to define an animal's true disease status. **Kappa Statistic:** is that agreement between tests is evidence of validity, whereas disagreement suggests that tests are untrustworthy. **MANAGEMENT & PRESENTATION OF DATA** **DATABASE:** a structured collection of data, and is the basis of an organized data storage and retrieval system.​ A database containing animal records includes different types of data that comprise different components of the records.  ​ Some of these are **Tombstone Data** and therefore case-specific; others change from one consultation to another, thus being record-specific.​ **DATABASE MODELS:** - **Record Model --** the traditional way of structuring data. This is a useful approach for the clinician concerned mainly with patient care. - **Hierarchic Model --** data are stored in nodes which are arranged in a tree-like structure. - The uppermost level of the hierarchy has only one node; it is called a **root**. - Every node (except the root) is related to a single node at a higher level called its **parent**, and the multiple nodes at its lower level are its children. - **Network Model --** allows relationships to occur between many data components and is therefore of epidemiological value because it allows correlation of determinants with disease if the determinants and diseases are components of the network. - **Relational Model --** all data are represented by two-dimensional models which have the following properties: - Entries in the table are single-valued, neither repeating groups nor arrays are allowable; - Entries in any one column must all be the same kind; - Each column has a unique name and the order of columns is immaterial; and - Each row has a unique name and the order of rows is immaterial. **VETERINARY RECORDING SCHEMES:** **SCALES OF RECORDING (the types of Veterinary recording schemes were classified by Hugh-Jones (1975):** - **Microscale schemes** -- concerned with internal disease problems in separated populations such as those on farms and research institutes. - **Mesoscale schemes** -- involved with more widely distributed disease problems; e.g. data collection at abattoirs, diagnostic laboratories, and clinics. - **Macroscale schemes** -- designed to collect data with the purpose of gaining an international or national view of the disease. **VETERINARY INFORMATION SYSTEMS** - **Information -** comprises data that have been processed and organized for some purpose so that someone can extract meaning from them. - **System** - is generally defined as an entity comprising at least two related components. - **Information system** - in practical veterinary context, may be considered as collections of disease-related data that are integrated to satisfy the informational requirements of its users. **Data collection may be passive or active:** - **PASSIVE COLLECTION** utilizes existing data sources. - **ACTIVE COLLECTION** is gathering data specifically to fulfill the requirements of the information system. **EXAMPLES OF VETERINARY DATABASES & INFORMATION SYSTEMS:** - **Office Internationale des Epizooties disease reporting system** -- an international organization concerned with the global control of animal disease. - **NAHMS (National Animal Health Monitoring System) --** a macroscale system, designed to measure the incidence, prevalence and cost of health-related events in livestock in the US, and to identify determinants of disease in modern production systems. - **HIN (Animal Productivity and Health Information Network) --** established in the late 1980's at the Atlantic Veterinary College, Prince Edward Island, Canada to provide pig, beef and dairy farmers on Prince Edward Island with information to increase production efficiency. - **Danish swine slaughter inspection data bank --** database comprising post-mortem information on pigs collected at slaughter; acts as a mesoscale and macroscale scheme. - **VMDB (Veterinary Medical Data Base) --** a collaborative mesoscale data base involving several veterinary schools in North America. - **VIDA (Veterinary Investigation Diagnosis Analysis) --** a mesoscale database comprising records of specimen submissions to veterinary investigation laboratories in Great Britain. **TABULAR PRESENTATION OF DATA** Tables provide a compact way of presenting large sets of detailed information. **ESSENTIAL PARTS OF A STATISTICAL (EPIDEMIOLOGICAL) TABLE:** - **Table number:** tables should be numbered (with Arabic numerals) consecutively as they appear in the article or report. - **Title:** should give complete information as to the 'what', 'who', 'where', and 'when' of the table. It should be self-explanatory; and it sets the tone of what is to be expected from the table, no more or no less than what it indicates. - **Column headings:** basis of classification of the columns or vertical series of figures. They should be centered on all the columns on which they belong. - **Row headings or stubs:** basis of classification of the rows or horizontal series of figures. If the stubs exceed the space allotted for it in the first line, the text on the succeeding line should be indented to the third character. - **Body:** The intersection of a row and a column in a table is called a **cell**. Figures within the cells for a particular column should be aligned by the decimal points. - **Footnotes:** small letters, rather than numbers, should be used to designate footnotes since these are usually placed beside figures in the table. All footnotes should be placed immediately below the bottom rule of the table. - **Source of Data:** When the data presented are not original, it is obligatory to specify the source. The citation of the source is the last piece of item of the table and is placed after the footnotes if there are any. **POINTERS IN THE CONSTRUCTION OF A TABLE** **Simplicity, clarity and directness are prime considerations in the construction of tables.** **Clarity:** means that a table should jive with the textual discussion and does not appear out of place. Internally, clarity is achieved in many ways such as having clear, concise headings or captions. **Directness**: implies that what is only necessary should be included in the table; details that only serve to fill up space, especially those with the potential to distract, should be left out. **MASTER TABLE:** single table which shows the distribution of observations across several variables of interest in a given study. **DUMMY TABLE:** any table which do not contain figures but which give a preview of what table outputs may be expected from the study. These are prepared during the preparation of the protocol and prior to any tabulation. **TYPES OF GRAPHS:** - **Bar Graph/Chart/ Diagram (horizontal or vertical):** used for comparisons of counts, rates, etc between categories. - **Histogram:** a graphic representation of the frequency distribution of a continuous variable or measurement including age groups. - **Pie charts:** is a circle in which individual characteristics are represented as slices, the angle of a segment being proportional to the relative frequency of the said characteristic. - **Box and whisker plots:** its horizontal line indicates the median; the upper and lower extremities of the vertical lines (the 'whiskers') mark the maximum and minimum values of the data set; the horizontal sides of the large rectangles (the 'boxes') represent the quartiles. - **Control charts:** a suitable technique for monitoring data when they accrue sequentially; these are graphs on which successive results are plotted in a sequence while recording. - **Shewhart charts:** the change in a variable's value can be monitored easily over a period of time by plotting values on squared graph paper with time as the horizontal axis. - **Cusum charts:** a more sensitive method for detecting small changes; it consists of a continuous plot (usually against time) of deviations of cumulative sum ('cusum') value of the monitored value from its reference value.