POPM 3240 (M1) Questions With Complete Solutions
Define bias, random error, and systematic error. Correct
Answers Bias --> any systematic error in the design, conduct, or
analysis of a study that results in a mistaken estimate of an
exposure's effect on disease
Random error --> due to sampling/chance, corrected by
increasing sample size
Systematic error --> due to design flaws, affects validity
consistently (in the same direction), 3 types --> selection,
information, and confounding
Define target, source, and study populations. Correct Answers
Target population --> the population the study aims to assess
(ex: First Nations people in Canada)
Source population --> population from which the study subjects
are drawn; must be able to list all members of this population
(ex: First Nations people in Ontario)
Study population --> the population of individuals sampled for
the study (20 people from each of the 10 reserves in Ontario)
Define the following temporal patterns of disease: sporadic,
endemic, epidemic, and pandemic. Correct Answers Sporadic --
> disease occurs only occasionally in a population (ex: rabies)
Endemic --> disease is habitually present at an expected level
within a certain geographic area (ex: chicken pox)
,Epidemic --> disease appears at a rate that substantially exceeds
the expected levels within a given population (ex: H1N1)
Pandemic --> disease crosses international boundaries;
worldwide epidemic (ex: SARS)
Differentiate between external and internal validity. Correct
Answers External validity = how well the results from the study
population can be extrapolated to the target population
Internal validity = how well the the study relates to the source
population
Differentiate between means, proportions and ratios. Correct
Answers Means --> measure of central tendency (average)
Proportions --> measure where numerator is included in the
denominator (expressed as decimals, vulgar fractions, or
percentages)
Ratios --> fractional measure where the numerator is not
included in the denominator (expressed as A to B or A:B)
Differentiate between necessary cause and sufficient cause.
Correct Answers Necessary cause --> precedes the disease, if
not present the disease cannot occur (always present if the
disease is present)
Sufficient cause --> precedes the disease, if present the disease
always occurs
, Differentiate between sensitivity and specificity.
What do these tests indicated in respect to false negative and
false positives? Correct Answers Sensitivity --> how good a test
is at identifying diseased individuals as diseased. Sensitivity
tells something about false negatives (% FN = 1 - Sn) - when a
highly sensitive test yields a negative result disease can
confidently be ruled out.
Specificity --> how good a test is at identifying non-diseased
individuals as non-diseased. Specificity tells something about
false positives (% FP = 1 - Sp) - when a highly specific test
yields a positive result disease can confidently be ruled in
Differentiate between the terms colonized, infected and
diseased. Correct Answers Colonized --> agent establishes itself
in/on the host but does not generate an immune response
Infected --> host is invaded by microorganisms that multiply
and generate a immune response in the host
Diseased --> infection causes clinical signs/symptoms
Differentiate between the terms health, disease, and illness.
Correct Answers Health --> state of complete physical, mental,
and social wellbeing (not merely absence of disease)
Disease --> physiological/psychological dysfunction
Illness --> awareness of being unwell
Define bias, random error, and systematic error. Correct
Answers Bias --> any systematic error in the design, conduct, or
analysis of a study that results in a mistaken estimate of an
exposure's effect on disease
Random error --> due to sampling/chance, corrected by
increasing sample size
Systematic error --> due to design flaws, affects validity
consistently (in the same direction), 3 types --> selection,
information, and confounding
Define target, source, and study populations. Correct Answers
Target population --> the population the study aims to assess
(ex: First Nations people in Canada)
Source population --> population from which the study subjects
are drawn; must be able to list all members of this population
(ex: First Nations people in Ontario)
Study population --> the population of individuals sampled for
the study (20 people from each of the 10 reserves in Ontario)
Define the following temporal patterns of disease: sporadic,
endemic, epidemic, and pandemic. Correct Answers Sporadic --
> disease occurs only occasionally in a population (ex: rabies)
Endemic --> disease is habitually present at an expected level
within a certain geographic area (ex: chicken pox)
,Epidemic --> disease appears at a rate that substantially exceeds
the expected levels within a given population (ex: H1N1)
Pandemic --> disease crosses international boundaries;
worldwide epidemic (ex: SARS)
Differentiate between external and internal validity. Correct
Answers External validity = how well the results from the study
population can be extrapolated to the target population
Internal validity = how well the the study relates to the source
population
Differentiate between means, proportions and ratios. Correct
Answers Means --> measure of central tendency (average)
Proportions --> measure where numerator is included in the
denominator (expressed as decimals, vulgar fractions, or
percentages)
Ratios --> fractional measure where the numerator is not
included in the denominator (expressed as A to B or A:B)
Differentiate between necessary cause and sufficient cause.
Correct Answers Necessary cause --> precedes the disease, if
not present the disease cannot occur (always present if the
disease is present)
Sufficient cause --> precedes the disease, if present the disease
always occurs
, Differentiate between sensitivity and specificity.
What do these tests indicated in respect to false negative and
false positives? Correct Answers Sensitivity --> how good a test
is at identifying diseased individuals as diseased. Sensitivity
tells something about false negatives (% FN = 1 - Sn) - when a
highly sensitive test yields a negative result disease can
confidently be ruled out.
Specificity --> how good a test is at identifying non-diseased
individuals as non-diseased. Specificity tells something about
false positives (% FP = 1 - Sp) - when a highly specific test
yields a positive result disease can confidently be ruled in
Differentiate between the terms colonized, infected and
diseased. Correct Answers Colonized --> agent establishes itself
in/on the host but does not generate an immune response
Infected --> host is invaded by microorganisms that multiply
and generate a immune response in the host
Diseased --> infection causes clinical signs/symptoms
Differentiate between the terms health, disease, and illness.
Correct Answers Health --> state of complete physical, mental,
and social wellbeing (not merely absence of disease)
Disease --> physiological/psychological dysfunction
Illness --> awareness of being unwell
