Which of the following are not threats to internal validity (select all that apply)?

1. Accuracy of assessment of disease
2. The intervention is not feasible in a real-world setting
3. Selection bias of controls
4. Appropriate calculation of measures of association
5. Comparability of study groups

In a randomized controlled trial, patients with meningitis who were treated with corticosteroids had lower rates of death, hearing loss, and long-term neurological effects. Which of the following is a randomized comparison?

a) Patients who remained for the duration of the trial versus those who dropped out after randomization.

b) Patients who responded to the disease versus those who did not.

c) The sample of patients who took the drug before being randomized and developed the disease.

d) The sample of patients who, at the time of randomization, were severely affected by the disease

Which of the following statements are true about bias in epidemiological studies? (Choose 1 best answer) Random, non-systematic deviation of the study results from the truth (measurement error) causes bias    Non-random, systematic deviation of the study results from the truth causes bias   Bias can be detected by examining p-values   Bias can be detected by examining confidence intervals