Lecture 10- Association and causation

define and illustrate causal association

X causes Y

o High dietary sugar intake 'causes' diabetes

define and illustrate non-causal association

x does not cause Y

o Example: A third factor may be related to both preference for dietary sugar and occurrence of diabetes

Identify the five criteria for defining causation.

• Consistency

• Strength

• Specificity

• Temporality

• Coherence

Two models of multifactorial causality

o Epidemiologic triangle

o Web of causation

Examples of multifactorial causation

o Specific exposures (e.g., smoking)

o Family history

o Lifestyle characteristics

o Environmental influences

what is multifactorial causation

Many types of causal relationships involve diseases with more than one causal factor

dependent variable

a factor that is influenced or changed by another factor

In studies and observations, most outcomes are ______________ variables

dependent

independent variables

factor that stands alone and isn't changed by the other factor you are trying to measure

examples of independent variables

species, breed, sex, age, vaccination status, etc.

confounding variable

interference by a third factor that distorts the association within a study of two primary variables

define probability

Chance or risk of an event occurring (a proportion)

how do you calculate probability

o Probability= no. of times an event occurs/no. of times an event can occur

o A ratio that tells how likely an event is to take place

number of favorable outcomes (or in question)/number of all possible outcomes

define odds

ratio of the probability of an event occurring to the probability of an event not occurring

ex. Ratio of the number of successes to the number of failures

how do you calculate odds

P/(1-P)

what is the relationship between probability and odds?

o Probability varies between 0 and 1

o Odds varies between 0 and ∞

o They are directly related

o If you know one, you can easily calculate the other

The first number is the same in each case

The second number can be derived from the definition