Community 2

• Terminology

  The study of health and disease in populations, and how these states are influenced by heredity, biology, physical environment, social environment, and ways of living is what

  epidemiology
• Epidemiologic study requires that disease

  be measured quantitatively
• EPIDEMIOLOGY

  • Investigates the factors and conditions that determine the occurrence and distribution of health, disease, defects, disabilities, and deaths among individuals
  • focus is on the comparison between groups or defined populations
• Epidemiologic triangle

  • Host : Susceptibility and resistance through various processes
  • Agent : biologic or mechanical means of causing disease, illness, injury or disability.
  • Environmental : physical, sociocultural, sociopolitical and economic components

  
• 5 Characteristics of Epidemiology

  1. Heredity: a person’s genetic makeup
  2. Biology: age, gender, race
  3. Physical environment: sanitation levels, food and water supplies, air quality, occupational hazards, housing quality, neighborhood characteristics
  4. Social environment: educational attainment, cultural beliefs and practices, neighborhood quality
  5. Lifestyle: smoking, exercise, dietary patterns, dental attendance, toothbrushing habits
• Evidenced Based Decision Making (EBDM)

  • Systematic review - all previously published research that fit into the precise research question - good for EBDM
  • Systematic review with the addition of a meta analysis-combination of all results using statistical methods to come up with new information - best for EBDM
• Sources of literature

  • Primary sources - original reports of new information, original thinking, a new discovery
  • Secondary sources - interpretations of primary sources, use evidence already provided or given - no new evidence
  • Tertiary sources - summarization of primary and secondary sources
• Three Main Types of Epidemiology study

  1. Observational
  2. Analytic
  3. Experimental
• Types of epidemiology study

  Observational/Descriptive

  • involves description, documentation, analysis and interpretation of data to evaluate a current event or situation
  • incidence – # new cases in defined period
  • prevalence - # persons affected by condition at any one time
  • count – sum of disease
  • proportion – count, denominator to determine prevalence
  • rate – count per time dimension

  
• Types of epidemiology study

  Observational approaches

  • Cohort - one group observed over time longitudinal/prospective
  • Case control - two groups compared
  • Cross sectional-one point in time cross-sectional rather than longitudinal
• Types of epidemiology study

  Analytical

  • determines the cause of disease or if a causal relationship exists between a factor and a disease
  • prospective – pop thru time
  • cohort – group with defined characteristic, observed over time
  • retrospective – uses observations or data collected in the past
  • cross-sectional – looks at a phenomenon at one pt in time
  • longitudinal – same group over extended time
• Types of epidemiology study

  Experimental

  • used when etiology of the disease is established and the researcher wishes to determine the effectiveness of altering some factor or factors; deliberate application or withholding of the supposed cause of a condition and observation of the result
  • Clinical trials as an example
  • Highest level of study designs
• Types of epidemiology study

  Experimental

  • Pretest-posttest design: measure the dependent variable before and after treatment intervention
  • Repeated measures design: dependent variable measured several times to see if independent variable effect on dependent variable persists
  • Cross over design: all groups receive the same treatments but in different orders after a washout period
  • Split Mouth design: assignment of equivalent pairs (experimental and control)
• Variables

  • Definition: a characteristic that varies within the population under study.
  • Independent variable: manipulated by the researcher to determine effect
  • Dependent variable: thought to be dependent on the independent variable
  • Relevant variable: The confounding variable needs to be controlled by the researcher
  • Extraneous variable: confounding variable not controlled in a study
• Collecting Data

  • Need to review the relevant available literature
  • Literature review may help to bring the topic into sharper focus
  • The researcher can design a study to evaluate the idea by emulating the research designs previously used
  • Researcher will plan how the study will be conducted and how the data will be collected
  • It is important during data collection that everything is calibrated, has validity and interrater & intrarater reliability
• Validity

  • The results of study accurately represent that presence or absence of the variable being studied. It studies what it intended to study. Accuracy.
  • Internal validity: technique being tested is responsible for the results being reported-not by another external factor
  • External validity: can the study be generalized to other situations and people? How well does the sample represent the population.
• Reliability

  • Intraexaminer (intrarater) reliability
  • each examiner is scoring equivalently time & time again; “extent to which the same investigator remains consistent in scoring techniques when using a data collection instrument”; requires training & experience
• Reliability

  • Interexaminer (interater) reliability
  • consistency exists between examiners; “degree to which different investigators can obtain the same results when using the data collection instrumentation on a population”; examiners must have an initial & continued agreement on the interpretation of evaluative criteria; training with repeated use of the dental index on subjects is required to achieve reliability
• Intraexaminer Reliability

  • Based on the assumption that the index is inherently reproducible, the ability of an examiner to record the same conditions the same way over time is defined as intraexaminer reliability.
  • For example, the examiner records conditions in a group of 10 -20 persons and then repeats the process a few hours to a few days later. It is long enough for the examiners memory to fade however a short enough time for the condition to remain the same
• Interexaminer Reliability

  • Two or more examiners are in agreement. It requires initial agreement on interpretation of diagnostic criteria, then a period of training with repeated patient examinations to ensure that examiners’ judgment are comparable
• Collecting Data

  • Need to identify the characteristics of the group involved in the study
  • Population: the entire group or whole unit of individuals with similar characteristics ~ may be very small or very large
  • Also known as the target population
  • To take a portion of the population is called sampling
  • Different techniques are used to choose the sample
• Sampling Techniques

  • Sample – “a portion of population that, if properly selected, can provide meaningful information about the entire population”
  • “a sample is examined when the researcher has neither the time, money, nor the resources to study an entire population.”
  • a sample may be random or nonrandom and may be representative or non-representative of a population
• Collecting Data

  • Random sampling provides the most external validity~each member has an equal chance of being selected
  • Case Study of 1939 US presidential election between Roosevelt and Landon.
  • When a random sample may not accurately assess the problem, a random selection of subjects from 2 or more strata of the population may be needed ~ Stratified sampling
• Collecting Data

  • Systemic sampling involves the selection of subjects by including every nth person on a list ~ may not be considered a true random sample
  • Purposive sampling and convenience sampling may introduce bias
• Convenience Sample

  • “used when access to the total population is not feasible; members of the available sample are numbered consecutively, and a table of random numbers is used for experimental and control group assignment.”
• Random Sample

  • “a sample composed of subjects who are chosen independently of each other, with known opportunity or probability for inclusion; increases external validity; controls inter-subject differences”
  • Satisfies the concept of EPSEM for sample selection (Equal Probability of Selection of Every Member)
• Nonrandomized Sample

  • “sample that is not randomly selected from a general population, therefore making generalizations to a larger population invalid, for example, convenience sample or intact groups; threatens external validity”
• Uses of Epidemiology

  • observe interactions among factors that affect disease or health status
  • evaluate risk factors – attributes that increase the likelihood of developing a particular disease or negative health condition in the future
  • develop preventive interventions – strategies to eliminate risk factors and to reduce occurrence of disease
• Qualitative research

  • Relies on language rather than on numbers
  • Used when numbers cannot explain or describe the concept/question
  • Methods used include interviews, focus groups, surveys, manuscripts, narratives

  Quantitative research

  • Relies on numbers to answer the concept/question
  • Data is collected and analyzed by applying statistics
  • Table 7.1 French Beatty contrasts qualitative versus quantitative research methods
• Measuring Oral Diseases

  Dental Caries Indices

  • DMFT
  • deft
  • RCI

  Gingivitis Indices

  • GI

  Periodontal disease indices

  • PDI
  • CPITN

  Oral hygiene indices

  • OHI-S

  Dental fluorosis

  • Deans classification for fluorosis
• Index

  • Is a numerical scale with upper and lower limits, with scores on the scale corresponding to specific criteria.
  • Any form of disease quantification, including proportions and rates
• Dental Index

  • abbreviated measurement of the amount or condition of disease in a population
  • graduated numerical scale with defined upper and lower limits designed to facilitate comparison with other populations classified by the same criteria and methods
  • aids in collection of data
• Irreversible Index

  • Is one that measures cumulative conditions that cannot be reversed: dental caries
  • measures cumulative conditions that cannot be reversed
  • e.g. dental caries
• Reversible Index

  • Gingivitis indices are examples of reversible indices since gingivitis is a reversible inflammatory condition. measures a condition that can be reversed
  • e.g., gingivitis is reversible
• Properties of an ideal index

  Validity

  • measures what it is intended to measure

  Reliability

  • measures consistently at different times; reproducibility, stability of measurement
  • Clear, simple and objective
  • Reproducible
  • Sensitive to shifts in disease in either direction
  • Acceptable to subjects involved
  • Amenable to statistical analysis
  • Clinically significant and meaningful
• Properties of an ideal index

  • Validity: The index must measure what it is intended to measure, so it should correspond with the clinical stages of the disease under study at each point.
  • Reliability: The index should be able to measure consistently at different times and under a variety of conditions. The term reliability is virtually synonymous with reproducibility, repeatability, and consistency, meaning the ability of the same or different examiners to interpret and use the index in the same way.
• Properties of an Ideal Index

  • Clarity, simplicity, and objectivity. The criteria should be clear and unambiguous, with mutually exclusive categories. Ideally, they should be readily memorized by an examiner after some practice.
  • Quantifiability. The index must be amenable to statistical analysis, so that the status of a group can be expressed by a distribution, mean, median, or other statistical measure
• Properties of an Ideal Index

  • Sensitivity. The index should be able to detect reasonably small shifts, in either direction, in the condition.
  • Acceptability. The use of the index should not be painful or demeaning to the subject
• Negative Reversal

  • Occasionally seen in longitudinal studies in clinical trials.
  • Is a change of diagnosis in an illogical direction over a period of time long enough for real change to have taken place.
  • Diagnosis of borderline lesions as caries inevitably results in some degree of negative reversals, so reversals are an inherent part of any clinical trial.
  • Consistency of the examiner will ensure that the negative reversals will be balanced by positive reversals.
• negative reversal

  • reversal
  • change in diagnosis in an illogical direction over a period of time long enough for real change to have taken place