lecture 2 Observational studies

95% Confidence Interval (CI)

There is a 95% chance that the interval contains the “true” relative risk.

Attenuation (Confounding)

When the Relative Risk (RR) approaches 1 after statistical adjustment for a confounder; this means that for an exposure that increases risk, RR decreases approaching 1 (e.g., 1.30 to 1.05), and for an exposure that decreases risk, RR increases approaching 1 (e.g., 0.65 to 0.85).

Case-cohort study

A method using data from a cohort study that compares cases (subset of population with disease) to the whole cohort.

Confounding Factor

A factor associated with both the exposure and the outcome, but it is NOT in the causal pathway (mediators are in the causal pathway). In the presence of a confounder, the estimated Relative Risk (RR) or p trend may be incorrect.

Correct Temporal Relationship (in Prospective Cohort Studies)

Exposure is measured before the development of disease.

Critical Thinking

A person is thinking critically only if he or she is attempting to assess or judge the merits of possible options in light of relevant factors or criteria.

Cross-sectional Studies

Studies that measure an exposure and an outcome at the same time (e.g., BMI and taste perception).

Criterial Thinking

Thinking in the face of criteria.

Effect Modification (Interaction)

A third variable (covariate) influences the association between outcome and exposure differentially at different levels (stratification).

Food Frequency Questionnaire (FFQ)

A limited checklist of foods and beverages with a frequency response section for subjects to report how often each item was consumed over a specified period of time.

"Hard" Disease Outcome (Observational Studies)

Typically measures disease outcomes such as Cardiovascular events, fatal and non-fatal events, examples include Stroke, Myocardial infarction (heart attack), Angina pectoris, Pulmonary embolism, Transient ischemic attack, and Peripheral arterial disease.

Mediator

A variable that is in the causal pathway between the exposure and the outcome. If a mediator attenuates the association, it suggests the mediator is mechanistically partly or fully responsible for the association.

Meta-analysis (Systematic Reviews)

Quantitative results derived from multiple studies. This typically involves the weighted average of multiple studies (study level analysis) or, less commonly, the pooling of individual data (patient/individual level analysis).

Null hypothesis

The assumption that there is no difference between groups.

Observational Studies

Studies that measure the association between exposure (dietary) and outcome (health).

P < 0.05

Indicates there is a statistically significant difference between groups.

P > 0.05

Indicates there is no statistically significant difference between groups.

PICOS/PICOTS

Tools for understanding papers in the course, components include Population, Intervention (RCT) or Exposure (Observational Studies), Comparison or Control Group (RCT) or Reference Group (Prospective Cohort Study), Outcome(s), and Time (duration/follow-up on exposure), and Study type.

Quality Appraisal Tools

A document or checklist that describes characteristics of well-written studies or articles, serving as relevant factors or criteria on which to make judgements.

Quartiles

Population divided into 4 intake groups.

Quintiles

Population divided into 5 intake groups.

Reference group (for Relative Risk)

The group for which the Relative Risk (RR) equals 1.

Relative Risk (RR)

A measure used in observational studies to quantify whether nutrient intake is related to disease risk. An RR > 1 indicates increased risk, and an RR < 1 indicates decreased risk.

Risk Factors (RCTs)

Examples include Hypertension, Inflammation, and Blood lipids, which are often measured as outcomes in Randomized Controlled Trials.

Sensitivity Analysis

Analysis of data by multiple methods and an assessment of whether the differences impact the interpretation of the results. It can also involve performing statistical analysis of risk with and without adjustment for a confounder.

Suppression

The phenomenon where adjusting for a confounder enhances the association between an exposure and an outcome.

Tertiles

Population divided into 3 intake groups.

Validation (of FFQs)

Means the method is compared to a more detailed measure of food intake, and there is good agreement between the result