study design

Question 1

recall the steps for EBVM

Answer 1

1) formulate an answerable clinical question
2) search for evidence to answer the question
3) critically appraise the evidence (study design, epidemiological measures, causality, bias and confounding)
4) apply answer to your patient
5) audit the outcome

• we are focusing on 3) specifically study design

Question 2

two types of study designs

Answer 2

descriptive and analytic

Question 3

3 descriptive studies

Answer 3

case report
case series
survey

Question 4

two categories of analytic studies

Answer 4

experimental and observational

Question 5

2 types of experimental studies
(analytic)

Answer 5

lab trial
clinical trial

Question 6

3 types of observational studies
(analytic)

Answer 6

case-control
cross-sectional
cohort

Question 7

how to distinguish between descriptive and analytic studies

Answer 7

ask what is the aim of the study

if it is to describe a population then DESCRIPTIVE

if it is to qualify the relationship between factors then ANALYTIC

Question 8

descriptive studies

Answer 8

• describes a population
• no comparisons between groups of study subjects
• no conclusions about associations
• no hypothesis is testes
• provides a picture of what happens in the pop

Question 9

analytic studies

Answer 9

• comparisons between groups of study subjects
• interferences about associations between exposures/ treatments and outcomes
• hypothesis is tested

Question 10

what kind of study is often the earliest study conducted on a new disease
- to characterize its symptoms
- to describe how it varies in relation to individuals, places and time
- to quantify its occurrence

Answer 10

descriptive studies

Question 11

case report study
(descriptive)

think reporting a cool case

Answer 11

• describes some newsworthy clinical occurrence such as:
• unusual combo of clinical signs
• experience w a novel treatment
• rare condition
• unusual manifestation of a common disease
• sequence of events that may suggest unsuspected causal relationships
• based on one or a few cases
• generally reported as a clinical narrative
• might provide valuable info to investigate further

Question 12

case series
(descriptive)

think case report but repeated

Answer 12

• shows that it can happen repeatedly (whereas a case report describes something that happened once or a few times)
• describe:
• unusual clinical course of condition
• common features among multiple cases
• patterns of variability among cases
• may provide valuable info about prognosis of condition

Question 13

survey
(descriptive)

think frequency and distribution, data from existing sources

Answer 13

• quantifies the frequency and distribution of selected outcomes in defined pops
• often uses data from existing sources (surveillance systems)
• can provide valuable info that lead later to analytic studies
• if info on both outcome and exposure collected, then study becomes a cross-sectional study

Question 14

for analytic studies how do we distinguish between experimental and observational

Answer 14

ask if analytic, did the investigator allocate treatments/ interventions?

if yes; experimental
if no; observational

Question 15

experimental studies

Answer 15

• investigator controls the allocation of animals to the study groups
• preferred design, when the treatment is easy controllable
• advantage; possible to control potential confounders through the process of randomization
• outcome is determined after following the animals over time
• classified as lab trial or clinical trial

Question 16

observational studies

Answer 16

• investigator does not influence the natural course of events for the study designs
• preferred design, if exposure is complex and not easy controllable
• advantage; wider array of hypothesis can be test
• can be divided into prospective or retrospective studied
• classified as cross-sectional, case-control, or cohort

Question 17

PICO vs PECO

Answer 17

PICO (experimental): pop, intervention, comparison, outcome

PECO (observational) pop, exposure, comparison, outcome

Question 18

which studies use PICO and which use PECO

Answer 18

analytic experimental: PICO (think experiment –> intervention)

analytic observational: PECO (observing the exposure)

Question 19

what do ALL study designs have

Answer 19

population and outcome

so
descriptive: PO
analytic:
experimental PICO
observational PECO

Question 20

ex of PICO vs PECO

analytical

Answer 20

• experimental; does palladia cure mast cell tumours in dogs
  PICO cuz intervention
• observational: are dogs with floppy ears more likely to get ear infection than those w pricked ears
  PECO cuz no intervention, looking at exposure of disease

Question 21

lab trial

analytic, experimental

Answer 21

• carried out under strict controlled lab conditions
• provides good evidence of causation
• often conducted in other species
• advantage complete control over experimental conditions
• disadvantage; relevance to real world conditions is doubtful

Question 22

clinical (controlled) trials

analytic, experimental

Answer 22

• carried out under real world condition
• used for the evaluation of therapeutic or preventative effects of interventions in the field
• often used to evaluate pharmaceutical products
• animals are exposed to all known and unknown factors in their natural environment
• animals followed overtime to measure one or more outcomes, such as the occurrence of disease or treatment success

Question 23

randomized control trials

Answer 23

• the researcher allocates the animal into treatment groups based on random allocation
• allocation to groups should/can be blinded

Question 24

how do you distinguish between the 3 observational studies (case -control, cross-sectional and cohort)

analytic observational

Answer 24

ask when were the outcomes determined

before exposure was determined; case-control

at the same time as exposure; cross sectional

some time after the exposure; cohort study

Question 25

case-control study analytic observational

Answer 25

- selection of a group of cases w the disease and a group of controls without the disease - comparison of the frequency of the exposure factors in the cases w that in the controls - usually conducted retrospectively using a databank of cases that have already occurred ex 2 groups: look at cases WITH the disease and look at controls WITHOUT the disease - subjects selected based on their outcome status - cases selected first - controls matched to cases but don't have disease - no prevalence and no relative risk can be calculated because cases represent unknown proportion of all cases from source pop

Question 26

advantages of case-control study

Answer 26

- well suited for rare (or low incidence) diseases, or diseases w a long incubation period, or conditions developing over a long period or time - quick to conduct - relative low cost - existing records can be used - allow to study multiple potential risk factors (exposures) for a single outcome - require fewer subjects compared to other study types

Question 27

disadvantages of case-control study

Answer 27

- cannot provide info on disease frequency in a pop - not suitable for the study of rare exposures - data collection relies on quality of past records - representativeness of the selection of animals to be studied is difficult to guarantee, especially for the control group - many sources of potential bias - calculation of odds ratio only

Question 28

cross sectional studies

Answer 28

- sample of the pop (individual animals) is taken at one point in time and is examined for the presence of the outcome and the exposure status regarding to risk factors - non directional, single point in time, similar to survey - used to determine prevalence and risk factors - best suited for time-invariant exposures such as breed, sex , etc - may be repeated over time to describe the course of a disease overtime

Question 29

advantages of cross-sectional studies

Answer 29

- when a representative sample is collected multiple parameters can be estimated; prevalence, proportion of exposed and unexposed, pop structure - quick to conduct - moderate cost - allows study multiple risk factors of disease - current records can be used occasionally - calculation of risk ratio and odds ratio

Question 30

disadvantages cross-sectional studies

Answer 30

- only snap shot in time - difficult to determine is exposure occurred before the outcome - difficult to investigate cause-effect relationships - unsuited to the study of rare diseases (because large sample size is required to obtain a sufficient number of cases) - unsuited to the study of disease of short duration - incidence in exposed and unexposed individuals cannot be estimated - potential of confounding between risk factors

Question 31

cohort study analytical observational

Answer 31

- selection fo two groups of non-diseased animals - one group exposes to a factor postulated to be a risk factor for disease and another unexposed - followed overtime and change in disease status recorded - prospective but can be retrospective

Question 32

advantages of cohort study

Answer 32

- provides disease incidence estimates - can be used to study multiple effects (outcomes) of one exposure - can be used to study rare exposures - less recall bias as in case control studies - can be adjusted for loss-to-follow-up - can be used to demonstrate temporarily; exposure occurs before the outcome - calculation of risk ratios, odds ratios, and incidence measures

Question 33

disadvantages of cohort study

Answer 33

- often require long duration - large groups necessary for rarer diseases - losses to follow up often occur due to death or withdrawal - expensive and resource intensive - groups may differ at beginning of study

Question 34

narrative review

Answer 34

no specific methods used for selecting sources of evidence more susceptible to unrepresentative reporting of evidence

Question 35

systematic review

Answer 35

relevant studies are systematically identified, appraised and summarized, using explicit and reproducible methods

Question 36

meta analysis

Answer 36

results from all relevant studies analyzed statistically to give an overall summary result