Study Designs For Healthcare Questions

Question 1

Learning objectives tick off

Answer 1

❖appreciate the enormous potential for harm from health care
❖recognise that you need to be able to find, appraise and interpret scientific evidence in order to ensure that your decisions are based on the best available evidence
❖recognise the main categories of healthcare research questions.
❖be able to match healthcare questions to the appropriate
research study design(s).
❖identify the key differences between the main types of epidemiological study designs

Question 2

What is EBM

Answer 2

“The conscientious, judicious and explicit use of current best evidence when making decisions about the care of individual patients”
3 components for EBM:
- best external evidence
- patient values and expectations
- individual clinical expertise

Question 3

What is aaaa

Answer 3

Assess - what type of healthcare question
Access - finding best evidence (validity and relevance)
Appraise - quality of evidence. Interpreting results.
Act - evidence relevant to my clinical practice

Question 4

Why is aaaa framework important

Answer 4

❖An essential professional and academic skill
❖Medical knowledge is continually evolving.
❖The medical profession frequently fails to use effective treatments.
❖Keeping up to date is a lifelong commitment for every doctor
❖You need to develop and use the skills to: find, appraise and act on research evidence.

Question 5

Why should EBM be used

Answer 5

Best treatments for patients
E.g. neonatal deaths due to thalidomide and advice for babes to sleep on stomach

Question 6

What are the categories of healthcare questions

Answer 6

1. Frequency
2. Aetiology
3. Prognosis - what happens to those who have it?
4. Effectiveness - treatments and side effects
5. Diagnosis
6. Patient experience - how patients day is affected

Question 7

What healthcare studies match the healthcare questions

Answer 7

Frequency - ecological, cross sectional
Aetiology + risk factors - case control, cohort
Effectiveness - RCT
Diagnosis - special cross sectional/ test accuracy study
Patient experience - qualitative research

Question 8

What can epidemiology studies of frequency be divided into

Answer 8

Descriptive - describe patterns of disease
Analytical - evidence for cause and effect. Risk factors/ treatments that affect frequency

Question 9

What are 2 types of descriptive studies

Answer 9

Population level - ecological
Individual level (surveys) - cross sectional, case report, case series

Question 10

What are descriptive studies

Answer 10

❖By definition observational
❖Used to answer questions about frequency and patterns of disease
-how much disease
-distribution of disease: time, place, person
❖Used for hypothesis generation. Often precede more resource intensive analytic studies

Question 11

What is a case report

Answer 11

• Case report: a detailed report of an unusual ‘condition’ or ‘occurrence’ in a single patient.

Question 12

What is a case series

Answer 12

• Case series: a detailed report of an unusual ‘condition’ or ‘occurrence’ in several patients.

Question 13

What is a descriptive study: cross sectional study

Answer 13

Also known as prevalence/ incidence study/ survey
a study in which information is collected in a planned way from individuals in a defined population at one point in time.

Question 14

What is the office for national statistics

Answer 14

Collects Health and social care data
‘Life expectancy and the impact of factors such as occupation, illness and drug misuse. We collect these statistics from registrations and surveys’.

Question 15

What is a descriptive study: ecological study

Answer 15

Definition
A study in which information is collected from a
whole populations to compare disease frequencies
• in one population at different points in time
(population defined temporally)
• between different populations (population defined geographically) at the same period in time

Question 16

Difference between ecological and cross sectional study

Answer 16

Both measure at one point in time
Ecological - population level
Cross sectional - individual level

Question 17

What do analytical studies investigate

Answer 17

Cause and effect questions

Question 18

What are the divisions of analytical studies

Answer 18

• Observational: researcher is an observer of exposures and
outcomes
• Interventional / Experimental: researcher allocates exposure and observes outcomes

Question 19

What are analytical studies

Answer 19

❖Key feature: explicit comparison of two or more groups of individuals
❖Aim is to establish whether an exposure causes an outcome (cause and effect)
❖Exposure may be harmful (eg smoking) or beneficial (nicotine replacement for smoking cessation)
❖Types
• Observational
• Interventional / Experimental

Question 20

What are analytic observational studies

Answer 20

❖Exposure is not under the control of the researcher because of ethical or logistical constraints, for example if investigating whether an exposure causes harm/ causes a disease
❖A ‘natural experiment’
❖Types:
• Case control
• Cohort

Question 21

What are the types of analytic observational studies

Answer 21

• Case control: study starts with identification of the outcome (eg disease)
• Cohort: study starts with identification of the exposure (eg risk factor)

Question 22

How to approach a Cause and effect Q: “Does smoking cause lung cancer?”
Case control

Answer 22

Cases - individuals with lung cancer
Control - individuals without
Look at smoking history of patients with lung cancer and patients without
Start with outcome and then investigate exposure
Can investigate multiple exposures

Question 23

What are case control studies

Answer 23

❖A case-control study compares those with a condition (cases) to those without the condition (controls). Subjects are grouped for comparison according to the outcome of study.
❖The level of “exposure” to one or more factors is measured and compared between the two groups (cases and controls).
❖If the level of exposure is higher in the cases than in the controls the exposure might be a risk factor.

Question 24

What are cohort studies

Answer 24

❖A cohort study compares those exposed to a factor of interest (exposed) to those not exposed to a factor of interest (non exposed). Subjects are grouped for comparison according to whether they have been exposed or not
❖The two groups are followed up over time and the amount of disease developing over a specified time period (incidence) is compared between the two groups (exposed and unexposed).
❖If the incidence of the outcome is higher in the exposed compared to the unexposed the exposure might be a risk factor.

Question 25

Difference btw case and cohort studies

Answer 25

Case: Condition vs no condition
Cohort: Exposures vs no exposure

Question 26

How to approach a Cause and effect Q: “Does smoking cause lung cancer?”
Cohort study

Answer 26

Individuals who smoke vs dont smoke
Follow them up over time
See proportion that develop cancer (via death certificate)
Can be multiple outcomes

Question 27

How to choose btw case and cohort study

Answer 27

-how many exposures do you want to capture?
-how many outcomes do you want to measure?
-how long between exposure and development of outcome?
-is the outcome rare or common?

Question 28

Why are case control studies preferred over cohort

Answer 28

Dont have to wait for outcomes to develop
Look for individuals with outcomes already

Question 29

Advantages of case control studies

Answer 29

1)Can investigate multiple exposures
2)Can only investigate one outcome
3)Recruitment is based on presence or absence of outcome, so do not have to wait for this to occur
4)Groups for comparison are based on the presence of the outcome: active case finding overcomes the problem of rare outcomes

Question 30

Advantages and Disadvantages of cohort studies

Answer 30

1)Can only investigate one exposure
2)Can investigate multiple outcomes
3)You have to wait for the outcome to occur after recruiting on the basis of exposure –so loss to follow up is a problem for diseases with long latency periods
4)For rare outcomes a lot of exposed individuals would need to be recruited to be sure of enough outcomes occurring.

Question 31

What are clinical trials

Answer 31

Type of analytical experimental studies

❖A controlled clinical trial is an experimental study where researchers decide whether participants receive the new intervention being tested or receive a control treatment, usually either the standard/existing treatment or placebo.
❖Controlled clinical trials are used to investigate effectiveness (does an intervention cause an improvement in health)
❖Participants consent to researchers deciding which treatment they receive
❖Randomised Controlled Clinical Trials (RCTs) have design features that increase their internal validity (reduce bias)

Question 32

What is a pre requisite for RCT

Answer 32

Pre-requisite for an RCT (experiment) is that there is genuine uncertainty about which treatment is best: equipoise… and that the new treatment will do more good than harm.

Question 33

Evidence for cause and effect hierarchy

Answer 33

RCT
Cohort study
Case control study
Case series and reports
Expert opinion

Question 34

What are healthcare questions about patient/ carer/ health professional experiences

Answer 34

Qualitative research
May want to know why patients have specific habits/ choices even though it’s proven their harmful
E.g. Why do patients continue to smoke despite evidence of harm and RCT evidence that nicotine replacement therapy is effective?

Question 35

What is qualitative research

Answer 35

❖Collection of non numerical data about people’s subjective understandings of their lives and experiences: ‘why and how’ rather than ‘how often’
❖In depth study of a small number of individuals in a specific setting rather than aiming for generalisability across different settings in quantitative research (which requires larger sample sizes)
❖Interpretation of the meaning of the data helps us understand individual’s behaviour and social phenomena

Question 36

What are the methods for collecting qualitative data

Answer 36

❖Multiple methods available for collecting data including direct observation of behaviour, individual interviews and group interviews (focus groups).

Question 37

Main messages of lecture

Answer 37

❖Health care can cause considerable harm.
❖Evidence Based Medicine is the use of current, best evidence when making decisions about the care of individual patients to avoid harm
❖Evidence Based Medicine includes accessing and appraising clinical research which can be done using the AAAA framework
❖Different healthcare questions require different types of research study design.
❖Healthcare questions can be divided into 3 types: those measuring frequency, those aiming to establish cause and effect relationships and other types: diagnostic test accuracy and individual experience
❖Questions about patterns of disease (time, place, person) are addressed by descriptive studies: cross sectional studies and ecological studies
❖Questions about cause and effect are addressed by analytic studies. Observational analytic studies (natural experiments) include cohort and case control designs. Experimental analytic studies (where the researcher controls exposure) are limited to exposures that are believed to be beneficial
❖Questions about individual experiences and beliefs that may help us to understand behaviour are addressed by qualitative studies, most commonly individual or group interviews (focus groups).