The Epidemiological Approach to Causation

Question 1

Sufficient cause

Answer 1

When it inevitably produces or initiatives an outcome and is termed necessary if an outcome cannot develop in its absence.

Question 2

Multiple Factors of Sufficient cause

Answer 2

A sufficient cause is not only a singular factor but comprises several components.

Question 3

Attributable fraction

Answer 3

Can be used to quantify the likely preventive impact of eliminating a specific causal factor.

Question 4

Casual pathway

Answer 4

Causes can be linked to a casual pathway where one factor leads to another until eventually the specific pathogenic agent becomes present in the organ that gets damaged; this can also be considered the hierarchy of causes.

Question 5

Rules for determining whether a specific living organism causes a disease:

Answer 5

1) The organism is present in every case of the disease
2) The organism must be able to be isolated and grown in pure culture
3) The organism must when inoculated in a susceptible animal, cause the disease.
The organism must then be recovered from the animal and identified.

Question 6

Factors of causation

Answer 6

Predisposing factors (genetics, etc)

Enabling factors (income, housing, etc)

Precipitating factors (exposure)

Reinforcing Factors (repeated exposures, etc)

Question 7

Interaction

Answer 7

Interaction between two or more causes is often greater than would be expected on the basis of summing the individual causes.

Question 8

A hierarchy of causes

Answer 8

Multiple causes and risk factors can often be displayed in the form of a hierarchy of causes where some are the proximal or the most immediate causes and others are distal or indirect causes.

Question 9

Temporal relationship

Answer 9

The cause must precede the effect

Self evident

In cases where cause is an exposure that can be at different levels, it is essential that a high enough level be reached before the disease occurs for the correct temporal relationship to exist.

Question 10

Plausibility

Answer 10

More likely to be casual if consistent with other knowledge.

Question 11

Consistency

Answer 11

Consistency is when several studies offer the same results. This is particularly important when a variety of designs are used in different settings, as the likelihood of every study making the same mistake is minimized.

Question 12

Strength

Answer 12

i. A strong association between possible cause and effect measured by the size of the risk ratio (relative risk), is more likely to be casual than a weak association which could be influenced by confounding or bias. Relative risks greater than 2 can be considered strong.

Question 13

Dose-response relationship

Answer 13

Occurs when changes in the level of a possible cause are associated with changes in the prevalence or incidence of the effect.

Strong Evidence of Casual Relationship between exposure and disease

Question 14

Reversibility

Answer 14

When the removal of a possible cause results in a reduced disease risk, there is a greater likelihood that the association is casual.

Question 15

Study Design & Causality

Answer 15

Experimental
- Well designed, relates effects of treatment and prevention measures

Cohort, and case-control
-bias is minimized, provides good evidence for the casual nature of association

Cross-sectional
-less able to prove causation, time sequence can be inferred from way of exposure and effect data collected

Ecological

• weakest link for casualty cuz of incorrect extrapolation
• time-series studies are useful to quantify effects