Additional information

General format for a 2 × 2 table

V1 + V0 = H1 + H0 = T

Internal validity: Internal validity asks whether the study’s design, conduct, and analysis answer the research question without bias. The presence of bias decreases internal validity.

External validity: External validity refers to how well the results of a study can be applied (generalized) to other situations, groups, or events. External validity is low if the study group is not representative of the general population.

Reliability and validity are terms used in the context of laboratory and clinical studies and their findings.

Comparison between validity and reliability

Reliability or precision

• Is it consistent?
• It doesn’t matter if it is correct; if it consistently gives the same result, then it is reliable.

Validity or accuracy

• Does it do what it is supposed to do?
• How well does it do it?
• Accuracy matters.

Clinical versus statistical significance

• Statistical significance is related to the probability that a study’s results are due to chance.
• Clinical significance refers to the magnitude and relevance of the actual treatment effect.
• With large sample sizes, even small treatment effects can appear statistically significant (e.g., a decrease in blood pressure by 2 mm Hg may be statistically significant but clinically of no value).

Intention to treat analysis: This is a method for analyzing results in a prospective randomized study in which all participants who are randomized are included in the statistical analysis and analyzed according to the group they were originally assigned to, regardless of what treatment (if any) they received. It includes participants who may have dropped out due to non-adherence to therapy.

How to increase the power of a study?

• Increase the sample size
• Increase the effect size*
• Increase the alpha value
• Decrease random error

a = true positives
b = false positives
c = false negatives
d = true negatives

When two events, A and B, are mutually exclusive, the probability that A or B will occur is the sum of the probability of each event.

When two events, A and B, are non-mutually exclusive, there is some overlap between these events.

Efficacy and effectiveness

Efficacy can be defined as the performance of an intervention under ideal and controlled circumstances, whereas effectiveness refers to its performance under “real-world” conditions.