Epidemiology Flashcards
epidemiology
is the study of populations in order to determine the frequency and distribution of disease.
both disease and health states
frequency of disease
burden of disease
what does epidemiology help identigy
risk factor for disease and determining optimal treatment approaches to clinical practice and preventative measures
- Can study risk factors as well as health/disease outcomes
- Can identify links, association and casualties
- Development and evaluation of preventative medicine
Cornerstone of evidence based practice
what is study in epidemiology
groups of people not individuals
first reported epidemiological case
John Snow and Broad St Pump cholera outbreak 1854
7 major role of epidemiology
Monitor infectious and non-infectious diseases
- Communicable and non-communicable diseases
Study natural history of diseases
- Prognosis and sequalae of disease
Investigation of disease risk factors
Health care needs assessment
Development of preventive programmes
Evaluation of interventions
Health Service planning
how are communicable diseases monitored
on a weekly basis e.g. flu
what is a consequence of a pandemic of an infectious disease e.g. flu
causes a number of deaths in elderly (linked to pneumonia) and additionally impact younger people too e.g. pregnant
how are non-communicable/chronic diseases monitored?
on a annual basis
e.g. cancer - incidence and death rates from cancer registries
oral example of self-limiting disease
ulcers
oral example of of chronic disease
chronic periodontal disease
oral example of fatal disease
oral cancer (50% will die in 5 year diagnosis)
oral example of unknown disease history
oral HPV
- unknown relationship with oropharyngeal cancer, need to carry out work to understand it
what is the purpose of epidemiologically studying the natural history of diseases?
sequalae of diseases (impact)
how can you epidemiologically investigate the risk factors (causes/determinants) of disease?
health needs assessment
- What care services are required by particular population groups
- Dependent on health status and demographics of population
- Collective population needs
Analytical epidemiology – unpicking risk factors
what does analytical epidemiology do
unpick risk factors (causes/determinants) of disease
how are preventative programmes developed
Based on knowing risk factors of diseases and attempting to prevent exposure to these factors
E.g. distribution of decay in Scotland of whole population
- 50% of 5-year-old in millennium
- 70-75% in most deprived
Develop programme to communities
- Universal and targeted practice for deprived areas
what is the purpose of using epidemiology to evaluate interventions
has a new service/procedure made any difference
3 main types of epidemiological study
descriptive (observational)
analytical (observational)
- case control
- cohort
intervention/experimental
- randomised controlled trials
what is epidemiology necessary for
health service planning
prevalence
measurement of all individuals affected by the disease within a particular period of time or point in time
- period, point in time, proportion
Number of affected individuals (cases is numerator) divided by total number of persons in population (denominator)
- Expressed as a % or fraction
what are prevalence estimates obtained from
obtained from cross sectional studies or derived from registers
prevalences used for
estimate of how common a condition is within a population over a certain period of time (carry out multiple) or point in time
e.g. % of P1 Children in NHS Greater Glasgow & Clyde with no obvious caries experience, 2008 & 2010 (different areas over 2 times)
incidence
a measurement of the number of new individuals who contract a disease during a particular period of time
- per week, per year (need to have time window expressed with rates)
Number of new cases or events during a specific period of time in a defined population
- Same numerator of cases, denominator is population
e.g. 5 new cases per week, 10 cases of oral cancer per 100,000 population per annum
incidence rates obtained from
longitudinal studies or derived from registers
diabetes - incidence Vs Prevalence
chronic incurable disease like diabetes can have a low incidence but high prevalence, because the prevalence is the cumulative sum of past year incidence rates
- Prevalence is cumulative sum of last year incidence rates
How many patients need diabetic drugs/care
common cold - Incidence Vs Prevalence
short-duration curable condition such as the common cold can have a high incidence but low prevalence, because many people get a cold each year, but few people actually have the cold at any given time (so prevalence low)
use prevalence or incidence for chronic disease?
prevalence
use prevalence or incidence for acute disease?
incidence
use prevalence or incidence for cancer?
Can be chronic but want to know incidence as people die quite rapidly
- Trend over time
But depends on nature of chronic disease
what are the 3 main variables in descriptive studies which partition individuals?
time (when)
place (where)
person (who)
possible different time measurements
dat circadian weeks months yearly
possible different place definitions
Globally (burden of disease – oral disease, caries),
countries,
MEDCs or LEDCs - Scottish Index of Multiple deprivation
towns,
communities/regions,
possible different person definitions
age
gender
ethnicity
3 aims of defined partitions in epidemiological studies
Identify changes in incidence or prevalence over time
OR
Determine incidence or prevalence of disease in different geographical areas
OR
Determine incidence/prevalence of disease in groups of individuals with different characteristics
Correlations may then be sought with other variables resulting in hypothesis of cause
descriptive epidemiology measures
the burden of disease
4 advantages of sample
reduces no. of individuals to be sampled
reduces cost
higher response rate
higher quality of information collected
what must a sample of a population be
Sample must be representative of population being investigated.
- Aim is to avoid bias or being skewed
why is sample size important
don’t need to ask everyone in population but must be representative so margins of error lie likely where true value is
5 sampling techniques
simple random sample
systematic sample
stratified sample
cluster sample
multi-staging sample
simple random sample
uses random number tables/generators
systematic sample
individuals selected at regular intervals from population list (every 2nd, 3rd)
- logical
open to bias (how they are ranked)
stratified sample
ensures small sub-groups adequately represented
e.g. Scottish index of multiple deprivation (into fifths)
cluster sample
use of groups as sampling units, e.g. school classes
- more practicable
multi-staging sampling
combines above techniques
- 20% of schools from each level of deprivation
what can occur if sampling process isn’t clear
error and bias in survey methodology
5 possibles errors that can occur due to unclear sampling techniques
Sampling bias / selection bias
- Skew data
Response bias / information bias
- Need to monitor who responds - could only be affluent educated (then miss a proportion)
Measurement error
Observer variation (intra- or inter-) - needs to be Standardised
Loss to follow-up
what are the 2 types of observer variation
- Inta – minimal, sampler is consistent, repeatability
- Inter – between samplers
what are indices used for
to measure disease need an appropriate index
Measuring for the purposes of epidemiological studies different from recording disease for patient treatment purposes
- More objective
- Not subjective description of decay
Standardised measurement
9 properties of an ideal index
clear, unambiguous, not subjective
ideally correspond with clinically important stages of the disease
indicate treatment need
within the ability of examiners
reproducible
not time-consuming
acceptable to patient (no harm)
amenable to statistical analysis
allow comparison with other studies
index for dental caries
DMF index
- first described in 1937
DMFT: decayed, missing & filled teeth (0-32)
DMFS: decayed, missing & filled surfaces (0-148)
- Distal, mesial, occlusal, buccal and lingual (incisors don’t have occlusal)
Deciduous teeth: dmf/def index
- dmf: deciduous decayed, missing and filled teeth (0-20)
- e = indicated for extraction / exfoliated
at age 6 (& over) only score “c, d, e”
6 limitations of the DMF index
Teeth extracted for reasons other than caries
- Perio, trauma, missing naturally (M wrong), overestimation
Influenced by access, e.g. interproximal surface
Difficulty in differentiating fissure-sealant from restorations – underestimate caries
Influenced by past disease activity
- Historical caries experience
- Not necessarily at the time you examine
Threshold criteria of disease can vary (must specify)
Cannot be used for root caries
level of decay used for DMF dental caries index
pulpal and decay in dentine
- both visible obvious decay
not enamel or sub-clincal decay
national dental inspection programme NDIP
Scottish dental epidemiological programme of children
- Renamed from SHBDEP (Scottish Health Boards’ Dental Epidemiological Programme) (1987 – 2000) in 2002
Cross-sectional, descriptive dental surveys of school children
Larger samples than UK decennial surveys
Involve standard examination criteria and trained and calibrated examiners
Target groups: children in P1 and P7
- Basic inspection for all children in P1 &P7 every year
Detailed inspection (epidemiology) for a sample of children every year
- Alternates each year between P1 and P7
- NHS Board can add additional year groups
- Sample more detailed DMFT sub-sample
aims and goals of NDIP
Aims to inform:
- parents of their child’s dental health status (Basic NDIP)
- advise Scottish Government, NHS Boards, and other organisations of the oral disease prevalence in children in their area (Detailed NDIP – Epidemiology survey)
like a census
goals
- to inspect a representative sample of the P1 or P7 LA school population in any year
- to determine current levels of established tooth decay
- to illustrate the impact of deprivation on the dental health of 5 & 11 year old children in Scotland
basic NDIP procedure
Offered to every child in P1 and P7 classes of local authority schools every year
Proportion of school rolls inspected 85-90%
Generates letter to parent
- Overall state of dental health of child
- Conveys degree of urgency with which appointment for attendance at dentist suggested for child
Not a detailed examination of each surface of each tooth
NDIP (detailed; epidemiology)
Detailed Inspection
- more rigorous and comprehensive assessment
- Calibration of examiners
- records status of each tooth surface in accordance with international epidemiological conventions (i.e. d3mft: caries into dentine)- can be underestimate
- Uses same clinical inspection criteria as SHBDEP - can therefore look at trends from 1987 re P1 children
goals of NDIP
- to inspect a representative sample of the P1 or P7 LA school population in any year
- to determine current levels of established tooth decay
- to illustrate the impact of deprivation on the dental health of 5 & 11 year old children in Scotland
how is calibration of examiners performed for epidemiology surveys
Number of children e.g. 10 selected for calibration exercise
- High proportion should have caries
Potential dental epidemiology examiners then all examine and chart each child
Compare results
- Assess inter-observer variation
- Each child should have same level of decay from every examiner
Outlier dental examiners not able to participate in epidemiological programme
index of orthodontic treatment (IOTN)
Assesses need and eligibility of children for NHS orthodontic treatment on dental health grounds (treatment need scale used on clinic for treatment planning)
Selects those children who will benefit most from treatment; fair way to prioritise limited NHS resources
Dental Health Component (DHC) has 5 Grades and Aesthetic Component (AC) has 1-10 scale
aesthetic component of index of orthodontic treatment
- scale of 10 colour photographs showing different levels of dental attractiveness
- AC used for border-line cases with Grade 3 DHC. If high AC score, NHS treatment is permissible
dental health component of index of orthodontic treatment
5 grades
- Grade 1: almost perfection, to
- Grade 5: for severe dental health problems
E.g. upper front teeth that protrude more than 9 mm
plaque indices
- Debris Index (Green & Vermillion, 1960)
- Plaque Index (Silness & Loe, 1964)
gingivitis indices
- Modified Gingival Index (Loe, 1967)
- Lobene Index (Lobene, 1986)
periodontitis index
basic periodontal exam (BPE, CIPTN)
3 indices used for periodontal disease
- plaque indices
- gingivitis indices
- periodontitis indices
types of fluorosis indices
- Fluorosis Index (Dean, 1934)
- TF Index (TFI) (Thylstrup & Fejerskov, 1978)
- Tooth Surface Index of Fluorosis (TSIF) (Horowitz et al, 1984)
- SCOTS Index (Scots HBs Child assessments of Opacities by tooth-Thirds & Symmetry) (Pitts & Stephen, 1991
when can fluorosis be detected
when upper anterior teeth erupt
- blotchy - issue aesthetically
is fluorosis a public health problem in Scotland?
Not considered a public health problem in Scotland
Low impact to patient and profession
Will be monitored through NDIP programme
- Potential impact of childsmile programme
- Due to increase in F in childsmile toothpaste (1450 ppm)
