Acquired immunity is best described by which of the following?  The body produce its own antibodies.  Immunity through transfer to the unborn child of a mother\'s immunity from disease.  Having had a dose of disease that stimulates the natural immune system.  Serial surveys involve which of the following?  Ecologic data  Cross-sectional data  Case-control data  Cohort data  ______ refers to an error that occurs if it is mistakenly assumed that, because the majority of a group has a characteristic, the characteristic is associated with those experiencing the outcome.  Bias  Ecologic fallacy  Confounding  Chance  The epidemic curve outlines the shape of which type of table or graph?  Line listing  Line chart  Pie chart  Histogram  Which study design may be appropriate when it is not possible to estimate an effect on the individual level?  Case series  Cohort  Ecologic  Experimental  Public health surveillance refers to which of the following activities?  Public health monitoring  Interpretation and dissemination of systematically collected data  Ongoing collection and analysis of community health data  All of the above activities are part of public health surveillance.  Which of the following descriptive study design allows us to determine effectively whether a given event preceded another?  Ecologic  Cross-sectional  Case study  None of the above  Which of the following descriptive study designs would you use if you wanted to collect exposure and disease data at the individual level and calculate prevalence estimates?  Ecologic  Cross-sectional  Case study  All of the above  Which of the following descriptive study designs can be useful for generating hypotheses?  Ecologic  Cross-sectional  Case study  All of the above
21.c
 Explanation: Due to a diseased state, the body encounters antigens (bacteria, virus etc.). Through proper medications, the diseased state is recovered; but the antigens present in the body, start eliciting an immune response for future attack of this bacteria. Immunity acquired via this means is known as acquired immunity. It is not innate; i.e. it is not acquired by the individual since birth. So, option (c) is the best answer.
 22. b
 Explanation: Serial surveys are cross-sectional surveys. They are conducted routinely. One good example is census.
 23. The correct answer is a.
 Explanation: Bias is a mistaken assumption, occurring at the time of research. It is very common in general research practices.
 24. d
 Explanation: Epidemic curve is always a histogram. It is a graphical display of number of persons found affected by the disease during an epidemic outbreak.