Study Designs

Question 1

Evidence Based Veterinary Medicine (5)

Answer 1

1. Formulate an answerable clinical question 2. Search for evidence to answer the question 3. Critically appraise the evidence a. Study design b. Epidemiological measures c. Causality d. Bias and confounding 4. Apply the answer to your patient 5. Audit the outcome

Question 2

Major types of study designs (2)

Answer 2

1) analytic 2) descriptive

Question 3

Analytic Study Designs (3)

Answer 3

Case reports Case studies Surveys

Question 4

Types of Descriptive Study Designs (2)

Answer 4

1) Experimental 2) Observational

Question 5

Experimental study designs (2)

Answer 5

1) Laboratory trial 2) Clinical trial

Question 6

Observational study designs (3)

Answer 6

1) Case control study 2) Cross-sectional study 3) Cohort study

Question 7

Components of descriptive study (3)

Answer 7

1) No comparisons 2) No conclusions about associations between exposures 3) No hypothesis is tested Description of what happens in populations Earliest studies conducted on new species/diseases/etc.

Question 8

Components of analytic study (3)

Answer 8

1) Comparative 2) Interferences about associations between exposures/treatments 3) A hypothesis is tested

Question 9

Case report (case study)

Answer 9

• Describes some ‘newsworthy’ clinical occurrence, such as (rare condition, unusual manifestation, previously unsuspected results) • Based on one or a few cases • Generally reported as a clinical narrative • Might generate hypotheses to be investigated further

Question 10

Case Series

Answer 10

much like it sounds multiple case reports on the same/similar topic (Mad cow disease for example)

Question 11

Survey

Answer 11

• Quantifies the frequency and distribution of selected outcomes in defined populations • Often uses data from existing sources • Hypotheses that lead later to analytic studies • Outcome and exposure information causes it to become cross-sectional

Question 12

Experimental studies

Answer 12

• Investigator controls the allocation of animals to the study groups (e.g. treated versus not treated) – E.g. vaccine trial, hormone treatment • Advantage: possible to control potential confounders through the process of randomization • The outcome (e.g. disease status) is determined after following the animals over time • Classified as: – Laboratory trial – Clinical trial

Question 13

Observational studies

Answer 13

• Investigator does not influence the natural course of events for the study subjects • Preferred design, if exposure is complex and not easy controllable • Advantage: wider array of hypotheses can be tested • Can be divided into prospective or retrospective studies • Classified as: – Cross-sectional studies – Case-control studies – Cohort studies

Question 14

Experimental vs observational

Answer 14

• (Experimental) PICO: interventions/treatments • (Observational) PECO: exposures/risk factors

Question 15

Laboratory trial

Answer 15

• Carried out under strict controlled laboratory conditions • Provides good evidence of causation • Often conducted in ‘other’ species • Advantage: complete control over the experimental conditions • Disadvantage: Relevance to ‘real-world’ conditions is doubtful

Question 16

Clinical (controlled) trials

Answer 16

• ‘real-world’ conditions • evaluation of therapeutic or preventive effects of interventions in the ‘field’ • Animals are exposed to all known and unknown factors in their natural environment • Animals are followed over time

Question 17

Randomized controlled trials

Answer 17

• The researcher randomly allocates the animals into treatment groups (computer generated or from tables) – This ensures that all factors associated with the outcome are ‘unbiased • Allocation to groups should be/can be blinded