9 - Methods in epidemiology

Question 1

Qualitative research

Answer 1

• Tends to focus on words instead of numbers
• Inductive view (generating new theories from the data)
• Interpreting data rather than modelling data
• Social properties are outcomes of the interactions between individuals

Question 2

Main research methods

Answer 2

• Participant observation (ethnography)
• Qualitative interviewing
• Focus group
• Language-based (including discourse analysis and conversation analysis)
• Documents-based analysis

Question 3

The main steps in qualitative research

Answer 3

1. Define the main research question
2. Selection of the relevant site(s) and subjects
3. Collection of relevant data
4. Interpretation of the data
5. Conceptual and theoretical work (grounded theory)

Question 4

Accuracy

Answer 4

• Reliability (external = replicability, very difficult; internal = more than one investigators)
• Validity (external = can results be generalized? internal = did other researchers came with the same conclusions?)

Question 5

Limitations of Qualitative Approaches

Answer 5

· The problem of adequate validity or reliability is a major criticism.
· Context can’t be replicated to any extent/generalisations be made to a wider context than the one studied.
· Time required for data collection, analysis and interpretation is lengthy.
· The researcher’s presence has a profound effect on the subjects of study.
· Issues of anonymity and confidentiality present problems when selecting findings.
· The viewpoints of both researcher and participants have to be identified and elucidated because of issues of bias.

Question 6

Strengths of qualitative approaches

Answer 6

· researcher gains an insider’s view of the field.
· Qualitative descriptions can play the important role of suggesting possible relationships, causes, effects and dynamic processes.
· Because statistics are not used, but rather qualitative research uses a more descriptive, narrative style, this research might be more accessible.

Question 7

Epidemics

Answer 7

• Outbreaks are often explosive, with long tails
• Can persist in some circumstances (endemic)
• Reintroductions
• Seasonal patterns

Question 8

Epidemiology – life history of infection

Answer 8

• Timings are pathogen-specific, and may be affected by host health
• The point at which an infected individual is registered as a case may be many days following their infection date

Question 9

What can modelling be used for?

Answer 9

1. understanding (explanation)
2. epidemic analysis
3. forecasting/ nowcasting
4. optimising control (prediction)

Question 10

1. understanding (explanation)

Answer 10

– Elucidate mechanism

– Estimate key biological / epidemiological parameters

Question 11

2. epidemic analysis

Answer 11

– Is current control working?

Question 12

3. forecasting / nowcasting

Answer 12

– Epidemic prediction

– Estimating hidden cases

Question 13

4. optimising control (prediction)

Answer 13

– Identifying most effective strategy with limited resources

– Identifying most cost-effective strategies

Question 14

The SIR model

Answer 14

• Individuals belong to one of three disease states: 
– Susceptible
– Infected
– Recovered, or removed
• Infected individuals infect susceptible individuals
• Infected individuals recover
𝑁 = population size
𝛽 (beta) = transmission rate
𝛾(gamma) = recovery rate

Question 15

Susceptible

Answer 15

dS/ dt = −𝛽𝑆 (𝑡) x 𝐼(𝑡)/N

Question 16

Infectious

Answer 16

dI/dt = −𝛽𝑆 (𝑡) x 𝐼(𝑡)/N − 𝛾𝐼(𝑡)

Question 17

Recovered

Answer 17

dR/dt = dI/dt = 𝛾𝐼(𝑡)

Question 18

𝑹𝟎 – the basic reproduction number

Answer 18

• The average number of cases generated by a single infected individual introduced into a totally susceptible population.
𝑅0 =𝛽/𝛾
• Knowing 𝑅0 allows us to estimate the final epidemic size of an outbreak and how hard it will be to control

Question 19

R0 meanings

Answer 19

• If 𝑅0 < 1 : the epidemic will die out
• If 𝑅0 = 1 : endemicity
• If 𝑅0 > 1 : the epidemic will take off