Lecture 5: Epidemiology of affective disorders and risk factors

Question 1

Which are the classes of epidemiology?

Answer 1

• Descriptive
• Analytic
• (teacher adds: treatment)

Question 2

What are the two types of interviews that can be conducted in epidemiological studies?

Answer 2

• Structured

- Semi-structured

Question 3

What are the two types of studies performed in descriptive epidemiology?

Answer 3

• Cross-sectional (to measure prevalence)

- Inception cohorts (to measure prognosis)

Question 4

What are the types of studies performed in analytic epidemiology?

Answer 4

• Cohort (to determine outcome. subtypes: prospective, retrospective, panel)
• Case control (to determine outcome in terms of odd ratio -mostly used in rare disorders)
• (teacher adds: ecological studies -compare clusters)

Question 5

Outline the types of studies that belong to descriptive & analytic epidemiology?

Answer 5

Descriptive (how the world is - generates hypotheses on risk factors associated with diseases):

• Cross-sectional studies
• Inception cohorts

Analytic epidemiology (test the hypothesis at individual level - i.e. risk factor exposure and disease development):

• Case control studies
• Cohort studies
• (Ecological Studies)

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Question 6

Outline the different types of interview and some pro’s and con’s associated with each?

Answer 6

Structured:

• Can be conducted by non-clinicians
• Increased reliability at expense of validity
• Low observer bias
• Can lead to false positives

Semi-structured:

• Requires clinicians/trained individuals
• Less reliable than structured interviews
• More validity
• Observer bias can occur with semi-structured interviews

Question 7

Outline how cross-sectional epidemiological studies function?

Answer 7

Measure prevalence in a defined population using a sample from the whole population.

All of the chosen sample is interviewed or a two stage sampling procedure is done

Question 8

What are the areas to assess the quality of a cross-sectional epidemiological study?

Answer 8

Cleary defined frame

Random sampling - i.e. everyone in the population has a chance to be included

High participation rates

A precise estimates of disease prevalence

If a two stage sampling procedure has been done - is there a screen for negatives?

Question 9

Give some examples of cross-sectional epidemiological studies?

Answer 9

Epidemiological Catchment Area Study, National Comorbidity Study, UK Adult Psychiatric Morbidity Study

Question 10

Describe how the UK Adult Psychiatric Morbidity study is conducted?

Answer 10

UK Adult National Psychiatric Morbidity Survey is conducted first by selecting postcodes - identify adults at these addresses - selecting them for participation - asking them to complete a structured interview CIS-R (assess prevalence of individual symptoms)

Question 11

What have been recent findings from the UK Adult National Psychiatric Morbidity Study?

Answer 11

Falling participation rates

The most common symptoms reported on CIS-R are sleep disturbance, irritability, fatigue, worry

Women have a higher prevalence of symptoms & CMD than men

The rate of CMD is rising

CMD are more prevalent in younger individuals

Those who are unemployed/economically inactive, in receipt of benefits or smoke more (> 15. a day) are more likely to have a common mental health disorder

Most prevalent CMDs are mixed/anxiety depression > GAD > Depression > Phobias > OCD > Panic Disorder

(Higher in women, younger individuals, unemployed/economically inactive and in receipt of benefits, or smokers)

Question 12

What are inception cohort studies and are they conducted?

Answer 12

Recruit participants at inception with aim of recruiting at same time (i.e. when disorder first recognised)

Follow up participants to identify prognosis

Should assess for a range of outcomes (with result analysis based upon baseline differences)

Critical analysis - look out for:

• High quality inception studies have good follow up rates
• Observer bias
• Representative cohorts (i.e. not recruited from a. tertiary centre)

Question 13

Give some examples of an inception cohort study

Answer 13

Collaborative depression study

• Patients with MDD treated in an academic centre
• Over 12 years - 59% of patient/weeks had minor, dysthymic or sub-threshold symptoms
• Mediation episode duration 3-6 months

NESDA

Question 14

How do cohort studies function?

Answer 14

Assess risk of developing a disease based on exposure to a risk factor

Individuals with the disease are excluded & participants are defined by exposure status

Follow up to determine outcome - displayed as relative risk

Question 15

Outline the types of analytic epidemiological cohort studies?

Answer 15

Prospective - classic design e.g. occupational cohort

Retrospective - opportunistic

Panel - series of cross-sectional based on same subjects

Question 16

What areas should be assessed in a cohort study?

Answer 16

Follow up rate - should be high

Any healthy worker effect - a form of selection bias that underestimates the prevalence of disease in a set of exposed individuals

Any observer bias

Type I error - false positives? - if accumulating multiple exposures?

Type II error - lack of true positive due to underpowered sample, especially the cases for rarer outcomes that may need a large sample size

Confounding variables?

Question 17

What is the healthy worker effect?

Answer 17

Form of selection bias that may underestimate prevalence of exposed individuals (exposed workers - typically seen in occupational cohort studies)

Underestimation occurs as the exposed works are compared to the general population

General population includes workers and non-workers.
As non-workers may have high rates of disease outcome (disease may affect them working) - prevalence of disease is higher in population > exposed workers

However better comparison is between exposed workers and workers

Question 18

How are case control studies conducted?

Answer 18

Recruit participants based on disease status then look for exposure

Works well if rare diseases and can assess for a number of exposures

What areas are particularly relevant for case control studies:

• Selection bias (recruit from 2nd care)
• Recall bias
• Observer bias
• Direction of causation - as recruiting on disease status
• Type I error if multiple exposures
• Types II error if rare exposures
• Confounding

Question 19

What did Cheasty et al find with a case control format?

Answer 19

Increased odd’s ratio of having depression if exposure to abuse

Question 20

How are ecological studies conducted?

Answer 20

Test data at a higher order cluster -i.e. postcode, region or country

Plot two variables against each other - suicide rates and unemployment

Allows a fast test of a hypothesis

However:

• Confounding bias - many covariates not controlled for
• Ecological fallacy - i.e in example above one individual who committed suicide may not be unemployed - is this a fair way to test

Question 21

Define the following concepts

a) Confounding
b) Selection bias
c) Observer bias
d) Recall bias
e) Type I error
d) Type II error

Answer 21

a) Where another variable can cause the outcome and the exposure
b) False outcomes from recruiting a non-representative sample
c) The measurer is influenced in their judgement by prior knowledge of participant status or by their knowledge of the study
d) Participant answers are influenced by their exposure - i.e. depressed mood and recall of +ve/-ve events
e) Type I error - false +ve
d) Type II error -not picking up a true association due to lacking statistical power

Question 22

Outline some structured/semi-structured interviews

Answer 22

Structured - CIS-R // CIDI

Semi-structured interviews - SCAN, SCID