Evidence-Based Veterinary Medicine

Question 1

What is a Type I error (α)?

Answer 1

Rejecting the null hypothesis when there is no difference between samples (null hypothesis is true)

Question 2

What is a Type II error (β)?

Answer 2

Accepting the null hypothesis when there is a difference between samples (null hypothesis is not true)

Question 3

What is statistical power?

Answer 3

• Probability of detecting a difference between samples
• =1 - β

Question 4

What is a cohort study?

Answer 4

• Measures incidence of disease in exposed and unexposed animals
• a cohort is a group of subjects who have shared a particular event together during a particular time span
• a group (cohort) of animals exposed to an hypothesized risk factor, and a group not
  exposed to the factor are selected and observed to
  record development of disease in each group
• Can estimate cumulative incidence

Question 5

What a case-control study?

Answer 5

• Used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the “cases”) with patients who do not have the condition/disease but are otherwise similar (the “controls”)
• a group of diseased animals (cases) and a group of non-diseased animals (controls) are selected and compared with respect to presence of the hypothesized risk factor.
• Disease triggers the recruitment
• Based on prevalence
• Measure frequency of putative casual factor in cases of disease, and healthy individuals
• Relatively quick
• Problem with confounding factors

Question 6

What is a cross-sectional study?

Answer 6

• Type of observational study that involves the analysis of data collected from a population, or a representative subset, at one specific point in time
• Based on prevalence
• Measure frequency of putative casual factor and disease in a sample of population (computerized databases, for example)
• involves the selection of a sample of n individuals from a larger population,and then the determination, for each individual, of the simultaneous presence or absence of disease and hypothesized risk factor prevalence is therefore recorded.
• Weak at inferring causality
• Samples will not always be representative samples

Question 7

What is prevalence?

Answer 7

Concept referring to the number of cases of a disease that are present in a particular population at a given time

Question 8

What is incidence?

Answer 8

• Number of new cases that develop in a given period of time

Question 9

What is the relative risk?

Answer 9

• Measured in a cohort
• = Incidence exposed/incidence unexposed

Question 10

What is the odds ratio?

Answer 10

• Can be used in cross-sectional study, cohort study, or case-control study
• The probability of an event happening to the probability of the event not happening
• Always bigger than the related probability
• Odds of diseaseexposed is the ratio of probability of disease-exposed/probability of no disease-exposed

Question 11

What is the prevalence ratio?

Answer 11

• Proportion of animals that have the disease