Test 2 Flashcards
An epidemic curve is based on information about the
Number of new cases
Which of the following are frequency measures?
a.) Prevalence
b.) Birth rate
c.) Incidence
d.) Mortality
All of the above
To calculate prevalence, what should you count?
All cases of the disease that can be detected in the population at a time of observation
When measuring the disease incidence, you must count what
Cases of the disease that have emerged since the start and until the end of the study period in a study population
What is incidence rate measured as
New cases per animal time at risk
When identifying the disease status of every animal in a population at a certain time point, we are able to determine:
Disease prevalence
Prevalence is expressed as..
A proportion
In a prevalence calculation, the ‘population at risk’ in the denominator consists of
All animals in the group that have been investigated for the disease
Calculating the disease incidence rate, the population at risk is
All healthy individuals in an exposed population during the observation period
The time at risk in the context of calculating incidence rate is expressed as
The sum of the length of time over all healthy individuals in a population at risk, when they remained healthy
Observing the health status of a population of healthy animals during certain time period and registering the cases of the disease emerging during that period – which of these can we calculate?
a.) Cumulative incidence
b.) Prevalence
c.) Morbidity
A.) Cumulative incidence
Calculating the proportion of dead individuals in a population, when taking into account all death cases appearing during the observation period, we get what
Cumulative mortality
To calculate a cause specific mortality rate, we need to know what aspects
The size of population at risk, and number of death cases due to certain disease (cause)
To calculate case fatality rate, it is necessary to know what
Number of diseased animals and the number of animals that died due to this disease
Among disease frequency measures, the one having measuring unit is
Incidence rate
The static measure of the disease in a population is
Prevalence
The test used to make a decision about the status of the patient is
Diagnostic test
Test that detects secondary changes which are indirectly predicting the presence or absence of disease or the disease agent is called
Surrogate test
Tests that are aimed to discover as many potentially diseased individuals as possible in the population are classified as
Screening test
Tests for detection of agents, responses or tissue changes that are directly associated with the presence of disease are classified as
Pathognomonic
Pathognomonic test detects
Signs and changes directly associated with the disease
What does analytical specificity express
Frequency of cross-reactions with other substances
What does analytical sensitivity express?
Detection limit of the test
How do you calculate sensitivity
TP / (TP+FN)
How do you calculate accuracy?
(TP+TN) / (TP+FN) + (FP+TN)
How do you calculate specificity?
TN / (FP+TN)
Accuracy of a test expresses what?
Probability by which an animal’s disease status is identified by the test correctly
Sensitivity of a test expresses what
Probability by which a diseased animal is identified by the test as positive
Specificity of a test expresses what?
Probability by which a non-diseased animal is identified by the test as negative
How do you calculate for positive predictive value?
TP / (TP+FP)
How do you calculate for Negative predictive value?
TN / (FN+TN)
How do you calculate for apparent prevalence?
(TP+FP) / (TP+FN) + (FP+TN)
How do you calculate for true prevalence?
(TP+FN) / (TP+FN) + (FP+TN)
By changing the cut off value of a test, what happens to sensitivity and specificity?
Both sensitivity and specificity
When changing the cut off value increases the specificity of the test, the sensitivity of the test does what?
Decreases
When combining two or more tests, the serial interpretation of test results does what?
Maximises the specificity of the test system
When combining two or more tests, the parallel interpretation of test results does what?
Maximises the sensitivity of the test system
What is meant by a sample?
Set of items or individuals selected from a larger group or population about which we wish to gather information from
What is a sampling unit?
- Object or individual that is selected from a population or group of objects individually, using some selection method
What is a list consisting of all sampling units?
A frame
The sampling frame is what
An individually identified population from where the sample is drawn from
To compile a sampling frame, it is necessary to
Identify all diseased individuals in a population
In case of probability sampling, by what methods are samples selected?
By random sampling
The simple random sampling takes place when?
When every animal has an equal probability to be selected
Cluster sampling is a sampling method where what
The groups of individuals are selected to be included in a study or subsets of individuals selected from those selected groups
A random sample is also a
Probabilistic sample
Systematic random sampling means that the animals are
Selected to the sample at certain interval
A systematic random sample is also a
Probabilistic sample
If you test only the animals who you can catch – what kind of sample is it?
A convenience sample
If an investigator involves in the study population only the animals with clinical signs, the sampling method is called
Purposive sampling
Stratified sampling is a sampling method where
Before sampling, the population is divided into subpopulations according to the factor possibly affecting the investigated parameter
Purposive sampling is also
Nonprobability sampling
Multistage sampling is a method where
Sample is drawn from units of different levels starting from highest
True or false: Sample size calculations for determination of prevalence of a disease in a population does not differ from the calculation of the sample size for disease detection
False
To draw a sample from a population, it is necessary to:
identify all individuals in a population
The fundamental difference between explanatory/analytical and descriptive studies is that
Two groups of animals or farms are compared and contrasted in explanatory study
True or false: confounding and bias are both examples of random error
False
Is random allocation of animals to groups required for laboratory experiements?
Yes
True or false: Laboratory experiments are usually relevant to what a clinician sees on day-to-day basis
False
Pick the right one; A descriptive study..
a.) Contains a group of control animals
b.) Explains the cause of a disease in nonquantitative terms
c.) Records events without making explanatory statements
C. A descriptive study records events without making explanatory statements
True or false: Misclassification bias is related to misclassification of disease and misclassification of exposure
True
True or false: Conclusions about the cause of a condition can be reliably made from a case report
False
Which of the following statements about surveys is true?
a.) Random and nonrandom surveys can be interpreted in same manner
b.) Most analytic techniques for surveys are based on assumption that some form of random sampling was carried out
c.) Surveys based on nonrandom samples never contain any useful information
B.
To which two major types can the explanatory/analytical studies be subdivided into?
Experimental and observational
Which of the following statements is false? Observational studies..
a.) Provide best information about a cause-and-effect relationship
b.) Are based on comparison of two or more groups
c.) Can be subdivided to cross-sectional, cohort and case-control studies
A.
True or false: Cross sectional studies can be used to help elaborate the time ordering of a cause and disease?
False
If the scales were old and consistently measure 500g too light, it may cause what kind of bias?
Information bias
What can confounding be controlled by?
Matching by-levels of confounders
Stratifying by-levels of the confounder
True or false: Differential misclassification occurs if the magnitude and direction of misclassification is different in the two groups being compared
True
True or false: Non-differential misclassification occurs if the magnitude and direction of misclassification are similar in the two groups being compared
True
Which of the statements is true: A case control study..
a.) Is often the only way to investigate the etiology of rare diseases
b.) Is usually conducted in a prospective manner
c.) Can only be used to investigate one potential cause
A.
True of false:Any type of bias can affect internal and external validity of the study,
True
When does unilateralism occur?
When factor A has no effect in the absence of factor B, but has considerable effect in the presence of B
When does synergism occur?
When the effect of factor A is in the same direction, but stronger in the presence of factor B
When does antagonism occur?
- When effect of factor A works in the opposite direction when acting in the presence of factor B, to the direction in which it acts in the absence of B.
True or false: Confounding is defined as; when the incidence rate of disease in the presence of two or more risk factors differs from the incidence rate expected to result from their individual effects
False
How can information bias be controlled?
By increasing the accuracy of the measurements
What does statistical significance indicate?
That the study results were probably not a result of chance alone
Clinical trial and laboratory study differ from one another in a way that a clinical trial uses what kind of animals
Animals in their natural environment
If the researcher only uses animals who lived in specific areas by specific roads, this leads to what kind of bias
Selection bias
How can selection bias be controlled?
By random sampling
If sample size was so small, and confidence intervals were wide, it is because of what kind of bias?
No bias
