Outcomes Test #1

Biological Gradient

"dose response" relationship between exposure and disease. Persons with increasingly high exposure have increasingly higher risks of disease. Some doses might not have a "dose response"effect but rather a "threshold effect" below which these are no adverse outcomes.

Specificity

-A single exposure should cause a single disease. -When present it specificity does provide evidence of causality, its absence does not preclude causation. -The weakest of all Hill's criteria; should be dropped.

Inferential Statistics:

-Not to describe characteristics of data but to infer or generalize from your sample to a larger population. -statistical inference: process of drawing conclusions from data that is subject to random variation (i.e. observational errors or sampling variation)

Temporality

-The causal factor must precede the disease in time. -Prospective studies do a good job of establishing the correct temporal relationship between an exposure and a disease. -Temporality is one of Hill's criteria that everyone agrees with.

Descriptive Statistics:

-provides a summarized view of the data obtained -includes measures of central tendency (means, medians, mode) and measures of variability (standard error, standard deviation)

4 Key features of Experimental Studies

1) Random Selection 2) Random Assignment 3) Use of a control group 4) Manipulation

Hill's Criteria to Assess Causation

1) Strength of association 2) Consistency 3) Specificity 4) Temporality 5) Biologic Gradient 6) Plausibility 7) Coherence 8) Experimentation 9) Analogy

Plausibility

Biological or social model exists to explain the association. association does not conflict with current knowledge of natural history and biology of disease. Problem: many cause effect relationships observed before biological mechanisms were identified.

Consistency

Causation is observed repeatedly in different persons, places, times and circumstances.

Inferential Statistics Examples

Chi squared Student's T-test Pearson correlation coefficient ANOVA Logistic regression

Analogy

Has a similar relationship been observed with another exposure and/or disease? Provides strong evidence for causation through prediction.

Experimentation

Invesegator-initiated intervention that modifies the exposure through prevention, treatment, or removal should result in less disease. Provides strong evidence for causation through prediction.

Coherence

Observed association is consistent with the natural course of the disease or outcome. Might consider this the positive flip side of the pitfall termed etiologic fallacy.

Descriptive Statistics Examples

Percentages Means Standards of Deviation Ranges

Hill's criteria with little support

Specificity, coherence, analogy, experimentation

The 5 Hill's Criteria that Schultz thinks are the best

Strength of association Biological Plausibility Consistency with results of other studies Temporality Dose response

Hill's Strongest Criteria

Strength of association Biological plausibility Consistency with results of other studies

Hill's Criteria that are frequently used

Temporality Dose response

Strength of Association

The stronger the association the more likely the association is to be causal.

Define: Mean- Median- Mode-

arithmetic average middle score most frequent score