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Epidemiology > Observational studies and routine data > Flashcards

Observational studies and routine data Flashcards

1
Q

What is an observational study

A

investigator does not interfere or manipulate exposure e.g case control, cohort

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2
Q

What is an experimental study

A

investigator determines exposure and who receives intervention e.g randomized control trials

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3
Q

What is the standardised mortality rate

A

rate ratio adjusted for age. It represents the ratio of the number of observed deaths in a particular population to the number that would be expected (E), if that population had the same mortality or morbidity experience as a standard population, corrected for differences in age structure.

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4
Q

What is the hierarchy of study design

A
  1. Systematic reviews and meta analysis
    1. Randomised controlled trials
    2. Cohort studies
    3. Case control studies
    4. Ecological
      1. Descriptive
    5. Case report series

As go up hierarchy studies become more robust and less susceptible to bias

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5
Q

What studies are used to determine accuracy of tests?

A

cross sectional design

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6
Q

What studies are used to determine disease prognosis?

A

Cohort study

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7
Q

What studies are used to determine the causes of disease factors

A

various non-randomised designs

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8
Q

What studies are used to determine population healthcare needs?

A

various, ecological aggregate studies

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9
Q

What studies are used to determine treatment efficacy

A

randomised trial

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10
Q

What is routine data?

A

Routinely collected and recorded in systematic way for administrative or statutory purposes

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11
Q

What are the types of routine data?

A

Health outcome data, e.g. deaths, hospital admissions and primary care consultations or prescriptions, levels of well-being from national surveys

Exposures and health determinant data, e.g. smoking, air pollution, crime statistics

Disease prevention data, e.g. screening and immunisation uptake

Demographic data, e.g. census population counts
Geographical data, e.g. health authority boundaries,

Births
Deaths
Cancer registrations
Notifications of infectious diseases
Terminations of pregnancy
Congenital anomalies
Hospital admissions
Community systems
GP consultation data
Prescriptions
Road Traffic Accidents
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12
Q

What are the advantages of routine data?

A
  • Cheap
  • Available
  • Standardised collection procedure
  • Comprehensive
  • Wide range of recorded items
  • Available for past years
  • Experience in use and intepretation
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13
Q

What are the disadvantages of routine data?

A
  • May not answer all question - not enough detail
  • Not every case capitured
  • Vairable quality and validity
  • Disease labelling may change over time or area
  • Coding changes may create artefactual increase or decrease in rates
  • Need careful interpretation
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14
Q

What are the uses of routine data?

A
  1. Survey: health survey england
  2. Performance management: quality and outcomes framework for GPs
  3. Other study design tend to collect own data

Must be careful when looking at changing coding rules

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15
Q

What are descriptive studies?

A
  • Describe distribution of factors or disease in relation to
  • May be individual: case reports, case series, cross sectional studies
      1. Person (age, sex, etc)
  2. Place (variation between countries)
  3. Time (variation over time)
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16
Q

What are cross sectional studies?

A
  • Used by healthcare providers to allocate resources
  • Can generate clues for hypotheses but not actually give you an answer (need to test in analytical studies)
  • Good at describing what people are like with respect to exposure presence or absence
  • Don’t know if exposure precede disease
  • E.g Health survey for England, 2001 and 2011 census, National Survey of NHS patients
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17
Q

What are the aims of cross sectional studies?

A
  • Annual data about nation’s health
  • Estimate population proportion with health condition
  • Estimate risk factor prevalence associated with said condition
  • Assess frequency of combinations of risk factors
  • Examine difference between population sub group
  • Monitor targets in health strategy
18
Q

What core topics are included in cross sectional studies?

A
  • General health and psycho social indicators
  • Smoking
  • Alcohol
  • Demographic and socio economic indicators
  • Height, weight, BP
  • Use of health services and prescribed medicine
19
Q

How is mortality measured?

A
  • Death certificates
  • Local registrars of birth and deaths
  • ONS for coding and processing
  • Produced as routinely published tables e.g General DH1, by area DH5, by cause DH2
  • Public Health mortality files
20
Q

How is cancer incidence measured?

A
  • Voluntary notification to local cancer registry
  • Also from death certificate
  • Useful for both incidence and survival
  • Being linked to hospital admission data and national clinical audits
21
Q

How are infectious diseases measured?

A
  • Look at disease rates
  • Reported by doctors to local authority or health protection team
    • E.g food poisnoing, meningitis, TB, plague
22
Q

What is the quality and outcomes framework?

A
  • Component of new General Medical services contract for GPs
  • Rewards practices for provision of quality care and helps fund further improvement in delivery of clinical care
  • Collected in national database
23
Q

What is administrative hospital admissions data?

A
  • Counts hospitals admissions
  • Episodes: finished consultant episode - time spent under continuous care of specific consultant
  • Admission: patient stay in hospital so more than 1 episodes and/transfer between hospitals
  • At end of episode can either go home, get transferred or die
24
Q

How is observed morbidity affected?

A
  • If can’t see GP no one will notice you’re ill and you end up in A and E
  • In A and E you might see a junior doctor who will chose to admit you or not
  • Might go back home and get worse
  • Admission criteria important
25
Q

What are the advantages of retrospective case control studies?

A
  • Mostly used in epidemiology
  • Quick and cheap
  • Can study cause of rare disease
  • Can invesitgate many exposure simultaneously
  • Better to have newly diagnosed cases because recall is better
26
Q

What are the disadvantages of retrospective case control studies?

A
  • Selection bias in control
  • Recall bias
  • Uncertain over exposure- disease relationship
  • Bad for rare exposure
  • Can’t directly calculate incidence rates
27
Q

How are conclusiosn drawn from case control studies?

A

Compare odds of being exposed in exposed in both cases and controls and then do odds ratio (odds of case multiplied by control)

28
Q

What is a control?

A
  • Originate from same study population as cases
  • At risk of disease
  • Compare exposure levels in cases with exposure levels in controls (prevalence)
    Defined eligibility criteria
29
Q

How are appropriate controls selected?

A

○ free from disease during same period in time in which case are identified
○ representative of population who would have been identified and included as cases
○ Could have from general population, neighbourhood, friends/relatives, hospital/clinic

30
Q

What are the pros of hospital controls?

A

○ match with cases in selection factors

○ Convenient, low cost

31
Q

What are the cons of hospital controls?

A

○ Medical conditions in control may be associated with exposure being investigated

Estimate of exposure hospital based rather than population based

32
Q

What are the pros of population controls?

A

random sampling

33
Q

What are the cons of population controls?

A

○ Expensive

○ Lower response rates

34
Q

What are the types of biases

A

see notes

35
Q

How are odds ratios calculated?

A

see notes

36
Q

What is the aim of cohort studies?

A

Aim: how much more likely is individual to develop disease if exposed to particular risk factor - relative to someone who is unexposed

  • Cohort: group of people who has something in common
  • Represents outcome free population from which cases (people with outcomes) eventually arise
  • Follow up people to see who get ill and why
  • Compare risk of outcome in exposed vs. Unexposed people
  • Can be done prospectively or retrospectively
  • Individuals selected on basis of exposure status and followed up over period of time
37
Q

What are the aims of a retrospective cohort study?

A
  • determines development of disease
  • Takes less time because doesn’t take a lot of time to assemble study population and determine disease status from present time
38
Q

How is a risk analysis carried out?

A
  • Compare risk in exposed to risk in non exposed

- Risk ratio: risk in exposed/risk in non exposed

39
Q

What are the advantages of cohort studies?

A
  • Able to look at multiple outcome
  • Able to follow through natural history of disease
  • Good design to look at risks related to rare exposure (can keep asking about exposure every follow up)
  • Incidence can be calculated
  • Can minimise bias in estimate exposure if prospective
40
Q

What are the disadvantages fo cohort studies?

A
  • Inefficient for studying rare disease (have to recruit thousands of people)
  • Expensive and time consuming if prospective
  • Loss to follow up may introduce bias
  • Healthy worker/volunteer may affect generaliseability
41
Q

What are logistical and ethical considerations?

A
  • Data availability
  • Cost of patient recruitement
  • Feasability/acceptability of intervention
42
Q

What are examples of cross sectional studies?

A

2001 Census
Health Survey for England
NHS Inpatient Survey on patient experience

Epidemiology (13 decks)

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