Nokea
Acid rain due to
- A. SO2
- B. H2SO4
- C. HCL
- D. b. and c
Correct Answer: D
Rationale: Acid rain forms primarily from sulfur dioxide (SO2) and nitrogen oxides reacting with water vapor.
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Identify the type of study design described: Questionnaires were mailed to every 10th person listed in the city telephone directory. Each person was asked to provide his or her age, sex, and smoking habits and to describe the presence of any respiratory symptoms during the preceding 7 days.
- A. Cohort study
- B. Case-control study
- C. Cross-sectional study
- D. Ecological study
Correct Answer: C
Rationale: This survey-based approach is characteristic of a cross-sectional study.
Level of resistance of a community or group of people to a particular disease is
- A. Passive immunity
- B. Active immunity
- C. Herd immunity
- D. None of them
Correct Answer: C
Rationale: Herd immunity refers to the resistance of a group to the spread of a contagious disease due to a significant proportion being immune.
Standard error is measure of
- A. Conceptual error
- B. Sampling error
- C. Instrumental error
- D. Observer error
Correct Answer: B
Rationale: Standard error quantifies the precision of the sample mean as an estimate of the population mean.
Selection bias interferes-
- A. internal validity
- B. external validity
- C. face validity
- D. all
Correct Answer: A
Rationale: Selection bias undermines internal validity by affecting the comparability of study groups.
Define the following terms: Experimental study
- A. A planned intervention where the investigator controls exposure to determine its effect.
- B. A study that uses historical data to analyze outcomes.
- C. A study conducted without a control group.
- D. A study where participants choose their own exposure.
Correct Answer: A
Rationale: An experimental study is characterized by the investigator's control over exposure.