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Veterinary Epidemiology > Study Designs > Flashcards

Study Designs Flashcards

1
Q

What are the 4 major types of study designs?

A
  1. DESCRIPTIVE: studies undertaken without a specific hypothesis
  2. OBSERVATIONAL: analytical, tests a hypothesis with time as an important characteristic
  3. EXPERIMENTAL: tests effect of an intervention in the field or lab
  4. RESEARCH SYNTHESIS: non-systematic and systematic reviews, meta-analyses
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2
Q

What are the 3 major types of descriptive studies? What do these studies describe?

A
  1. case reports
  2. case series
  3. survey

Is disease there?

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3
Q

What are the 2 major types of explanatory studies? What are some examples of each? What do these studies describe?

A

OBSERVATIONAL - no experiment being conducted, just observing
1. case-control
2. cross-sectional
3. cohort

EXPERIMENTAL - doing experiments
1. laboratory
2. controlled trials

explains associations - What changes disease status?

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4
Q

What are the 3 major types of research synthesis studies? What do these studies describe?

A
  1. non-systematic review
  2. systematic review
  3. meta-analyses

repeated associations - What consistently changes disease status?

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5
Q

How does the strength of evidence compare in all of the types of study designs?

A
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6
Q

What are case reports? What do they tend to focus on?

A

descriptive study of single (or very few) cases of rare or new conditions with unusual/new manifestation or management of a common condition

  • helps build a hypothesis
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7
Q

What are case series? What 2 things do they document?

A

descriptive study that describes clinical courses of a condition shared by a group of subjects in an area

  1. who/when/where
  2. prognosis estimation when representative of cases in the population
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8
Q

What do surveys describe? How is this done?

A

describe frequency and distribution of a condition in a population at a point in time —> just level of disease, no risk factors

  • focuses on one feature of disease and uses a questionnaire to properly sample and collect information
  • extrapolation is done when sampling is considered representative of the population
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9
Q

When are case-control studies done?

A

investigates risk factors for rare diseases —> outbreaks!

(observational)

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10
Q

Medical records for every dog in a country and details about exposure to benzidine and bladder cancer has been maintained for the first year of life. Why is a case-control study helpful in this situation? Can risk ratio calculations be used?

A

the entire population of dogs is a huge amount, where exposure to benzidine and bladder cancer is more rare —> maintain the diseased dogs and sample the population of non-exposed and non-diseased

NO —> randomly selected from the non-diseased group and the newly calculated risk (24%) is much higher than in the normal population (USE ODDS)

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11
Q

What is the time progression of case-control studies?

A

enquires about a study population, broken into cases vs. controls and exposed vs. non-exposed

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12
Q

What are 3 advantages of case-control studies? 3 disadvantages?

A

ADVANTAGES
1. efficient with rare disease
2. quick to undertake
3. cheap

DISADVANTAGES
1. no information on disease risk or incidence in the studied population
2. reliant on recollection of study participants
3. difficult to ensure unbiased selection of control group

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13
Q

What are cross-sectional studies? What 2 things do they commonly require?

A

observational studies that sample individuals from a population taken at a single or relatively short period of time —> “slicing through” a point in time or “snap-shot” that does not follow animals further

  1. surveys (sampling strategy) - going out and recording information
  2. questionnaires - paper filled out
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14
Q

What are 3 advantages to cross-sectional studies?

A
  1. quick
  2. can estimate risk (prevalence)
  3. cheap - no follow-up period
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15
Q

What are 3 disadvantages to cross-sectional studies?

A
  1. no information on disease incidence - slice of time, don’t know if disease is new/old
  2. not suitable for rare diseases or those of short duration - may miss disease due to time of study and incubation period
  3. difficult to investigate cause/effect relationships - don’t know if exposure occurred before disease
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16
Q

What are cohort studies? What time period does it occur in?

A

observational study that compares disease incidence over time among groups with different exposures

prospective or retrospective, with prospective being the strongest

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17
Q

What are 3 advantages to cohort studies?

A
  1. absolute incidence of disease in exposed and non-exposed
  2. exposure is recorded before disease
  3. well-suited for rare exposures with no need to reflect exposure prevalence from population —> good for new drug treatments that practitioners and farmers are trying
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18
Q

What are 3 disadvantages to cohort studies?

A
  1. long follow-up period makes it expensive
  2. losses to follow-up are problems that can introduce potential bias
  3. rare diseases require large groups ($$)
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19
Q

What are 4 hybrid observational studies?

A
  1. nested case-control
  2. case-crossover
  3. panel
  4. repeated survey
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20
Q

What are ecological studies? What is being analyzed?

A

observational study that measures exposure and summarizes measures of outcomes, making inferences of the individual level

groups —> cities, states, countries

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21
Q

What are 2 advantages and a disadvantage to ecological studies?

A

ADVANTAGES:
1. extremely quick and inexpensive
2. provides clues about associations between exposure and disease

DISADVANTAGES:
1. extremely prone to bias

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22
Q

What bias is common in ecological studies?

A

ECOLOGICAL FALLACY - assumption that an observed relationship in aggregated data will hold at the individual level

(these studies are not commonly taken seriously, but they can be a good place to start for hypotheses)

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23
Q

Explanatory studies, observational:

A
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24
Q

What is the difference between observational and experimental explanatory studies?

A

OBSERVATIONAL = no intervention

EXPERIMENTAL = intervention

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25
Q

What helps reduce variation in experimental studies? What is the main pro and con?

A

controlled settings

  • PRO: stronger evidence of causation due to it being prospective and fixation of confounders by design or random allocation
  • CON: limited range of hypothesis due to only being able to investigate one or few factors at a time and ethics (can’t test force minors to smoke to investigate the effects of smoking on their health)
26
Q

What are laboratory studies? What are the major pros and cons?

A

experimental studies with strictly controlled “in-house” conditions

  • PROS: highest level of evidence for causation
  • CONS: low-to-moderate level of relevance to the real world, expensive, time and labor intensive
27
Q

What are controlled trials? What are the major pros and cons?

A

experimental studies that account for real-world conditions

  • PROS: very high level of evidence for causation, highest level of relevance to the real world
  • CONS: very expensive, time and labor intensive
28
Q

How does the layout of laboratory studies and controlled trials compare?

A

LAB: homogenous subjects (genetics, age, other confounding factors) are randomly sorted into treatment and control groups and disease status is observed

CONTROLLED TRIAL: study subjects are taken from the population and are randomly sorted into treatment and control groups and disease status is observed

29
Q

What are some other names for controlled trials? What professionals carry these out?

A
  • randomized controlled trials —> keeps it general
  • [randomized, blinded, two-arm, placebo] [field, clinical, community] trial

trialists

30
Q

What are controlled trials? What are the 3 essential features?

A

study of an intervention (treatment, preventative factor) allocated randomly among animals naturally exposed to disease with the goal to test said intervention

  1. comparison group (alternative treatment) - often a control placebo/sham group
  2. random allocation - avoids selection bias
  3. blinding/masking - avoids information and selection bias
31
Q

What are the 4 groups present in controlled trials?

A
  1. Population with condition to begin with
  2. Intervention group - treatment, exposure
  3. Comparison group - placebo
  4. Outcome
32
Q

What are the 2 major biases associated with controlled trials?

A
  1. Hawthorne effect: participants in a trial tend to change many behaviors, regardless of intervention - taking better care of themselves, frequently going to the doctors
  2. placebo effect: beneficial event that cannot be attributed to the properties of the placebo itself
33
Q

Controlled trial bias toward improvement:

A

owners evaluated patient’s lameness as improving, when it was generally the same throughout the study

34
Q

In what 2 ways are participants in a controlled trial chosen to be included?

A
  1. intention-to-treat: all enrolled patients and randomly allocated to treatment are included in the analysis —> once randomized, always analyzed
  2. per-protocol: includes only those patients who completed the treatment originally allocated —> only those who perfectly followed protocol —> biased toward better results
35
Q

What way of including participants in controlled trials is recommended? Why?

A

intention-to-treat

avoids bias - the magnitude of effect depends on the adherence of the effect, depends on the adherence to assigned treatment strategy, making it represent the real world and pulls estimated toward the null hypothesis

36
Q

Why isn’t per-protocol typically preferred for controlled trials?

A

results better represent treatment effect, but it is prone to bias with untestable assumptions

37
Q

What is done at the end of controlled trials?

A

compare the risks of treatment and control groups

38
Q

What is the number needed to treat (NNT) in controlled trials? How is it calculated?

A

average number of patients who needed to be treated to prevent one additional bad outcome —> number of patients that need to be treated for one to benefit compared with a control

inverse of risk difference (1/RD)

39
Q

How is attributable risk/risk difference defined following a controlled trial?

A

RD = placebo risk - treatment risk

for every _____ patients treated, _____ recovered because of treatment

40
Q

How is number needed to treat (NNT) defined following a controlled trial?

A

NNT = 1/RD = 1/(placebo risk - treatment risk)

if ____ patients out of ____ benefit from treatment (RD), the NNT for one patient to benefit is about ______

41
Q

What is loss to follow-up in controlled trials? How should it be to ensure there is a balanced trial?

A

losses from the beginning of treatment to the follow-up period, commonly due to dropouts, death, moved away, and changes in treatment

  • should be minimal (<20%)
  • should be close to equal in each group: unbalanced = potential bias
42
Q

How can losses bring up bias in controlled trials?

A

if losses were related to the exposure AND the outcome = BIAS (untestable)

  • if patients who didn’t respond to treatment died or dropped out before the end of the study, the treatment effect could look much better than it actually is
43
Q

What are the 2 main ways to control biases in controlled trials?

A
  1. randomization - selection and confounding bias (uniformly allocate patients to both groups and evaluate similarities between them that may cause statistical differences, like weight, age, sex, breed)
  2. blinding - selection and information bias

randomize and blind…everything should be fine!

44
Q

What is the point of double-blinding in controlled trials?

A

patients and clinicians are both unaware of treatment allocation to avoid information bias

45
Q

What is a narrative review? What does it lack? Who conducts these studies?

A

research synthesis studies that tend to be subjective due to reviewer bias and weighing all studies equally, even if they do not have many participants

quantitative summary

conducted with subject-matter experts, possibly with pre-conceived notions

46
Q

What are narrative reviews commonly used for?

A

obtaining a broad overview of an area, NOT for decision-making

47
Q

What are 5 features of systematic reviews?

A
  1. specific question
  2. written protocol for review (transparent and repeatable)
  3. thorough literature review
  4. standard data extraction tool
  5. does not require subject matter expertise
48
Q

What are 4 purposes of systematic reviews?

A
  1. ensures all evidence considered
  2. minimizes potential for bias in drawing conclusions
  3. identifies gaps in knowledge - precursor of research
  4. policy decision
49
Q

What kind of information is extracted from systematic review?

A

qualitative - weighs studies based on assessment of quality of methods (more evidence = more priority)

50
Q

What happens when systematic reviews being to analyze quantitative information?

A

becomes a meta-analysis that extracts ORs, RDs, and other measured values and weighs studies based on result precision

51
Q

What are the 5 steps to systematic reviews? How does the end step compare in systematic reviews and meta-analyses?

A
  1. question formulation
  2. literature search
  3. relevance screening
  4. quality assessment
  5. data extraction
  • QUALITATIVE = systematic review
  • QUANTITATIVE = meta-analysis with pooled estimates and accounts for heterogeneity
52
Q

What happens at the data extraction step of systematic reviews? What 5 things are captured?

A

extraction of important data from all relevant primary research studies or studies of acceptable quality to summarize and/or synthesize results

  1. PAPER: general study information, like year, author, country, language, funding, and study design
  2. POPULATION: sampling frame, sub-populations, population attributes
  3. INTERVENTION: treatment, challenge, dosage, administration
  4. OUTCOME: types of test, test protocol
  5. RESULTS: type of data, effects estimates, statistics
53
Q

What dichotomous and continuous results are extracted during systematic reviews?

A

DICHOTOMOUS - OR, RR, RD/ARR

CONTINUOUS - mean difference, standardized mean difference

54
Q

How do quality summaries compare studies? What is the purpose of this step? When is meta-analyses not attempted?

A

by design and quality

identifies gaps in knowledge and common methodological issues

if heterogeneity is too large —> too much variation in outcomes, populations, etc.

55
Q

What is a meta-analysis? What are the 2 objectives?

A

statistical methodology used to combine data from two or more studies that have addressed the same question

  1. provides an overall estimate of an association
  2. explores sources of variation in the observed effect across studies
56
Q

What are the 5 advantages to meta-analyses?

A
  1. ensures all data considered has appropriate weight
  2. gains statistical power, allowing for small, non-significant results to contribute
  3. documents variability in study results
  4. investigates reasons for variability
  5. quantifies impacts of potential bias
57
Q

What is measured by meta-analyses?

A

QUANTITATIVE OUTCOMES —> OR, RR, RD, mean difference, standardized mean difference

(controlled trials are best)

58
Q

Meta-analysis:

A

weighted average treatment effects by their precision

(more precise = more weight)

59
Q

What extra advantage is present with meta-analysis?

A

can use a cumulative plot (1+2, 1+2+3, 1+2+3+4….) to see when sufficient evidence overtime was available to make a decision

60
Q

What bias is common in meta-analyses? How is it assessed?

A

publication bias - failure to publish results that are not statistically significant or unfavorable to study sponsor

funnel plots - X-axis = precision (standard error); Y-axis = treatment effect

61
Q

What 3 studies are applicable for meta-analyses?

A
  1. RANDOM CONTROLLED TRIALS*** - more standardized with clearly defined intervention/comparison groups
  2. observational studies - possible, but difficult due to issues with heterogeneity and prone to bias
  3. diagnostic test evaluation - estimates DSe and DSp

Veterinary Epidemiology (13 decks)

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