Research Design II week I

Baye’s theorem

start w prior belief (A), get new info (B), update belief (A given B)

what is the difference between the traditional decision-making process and evidence based decisions

addition of scientific evidence

theory

Justifications for treatment based on basic or applied work designed to answer the question why something should work

evidence

Justifications for treatment based on applied work (on patients) designed to answer the question if something works

the hierarchy of evidence describes _____ and _____

how a study is designed; the level of rigor associated with the design

hierarchy of evidence

background info, expert opinion, non EBM guidelines —> individual case —> cross setional studies —> cohort studies, case control studies —> non-randomized controlled trials —> randomized controlled trials —> critically appraised literature, EBP guidelines —> systematic reviews —> meta analysis

quality of evidence order

observational studies —> experimental studies —> critical appraisal

randomized controlled trial

A study in which people are allocated at random (by chance alone) to receive one of several clinical interventions. One of these interventions is the standard of comparison or control

advantages of RCT

• limits selection/confounding bias

• Blinding/masking to minimize bias (performance, detection bias)

• Results can be analyzed with well known statistical tools

• Populations are clearly identified

• Internal validity is stronger

Internal validity

the extent to which a study accurately estimates the causal effect of an intervention within the study population.

RCT disadvantages

•Expensive (time and money)

•Volunteer biases: the population that participates may not be representative of the whole

•Loss to follow-up attributed to treatment

•Can lack external validity

external validity

study findings cannot be generalized to other patients, clinicians, settings, or real-world conditions.

cohort study

one or more samples are followed and subsequent status evaluations with respect to a disease or outcome are conducted to determine which initial participants exposure characteristics (risk factors) are associated with it

retrospective vs prospective cohort study

retrospective: looks back

prospective: looks forwards

advantages of cohort study

•Subjects in cohorts can be matched, which limits the influence of confounding variables

•Well-defined intervention, criteria, outcome is possible

•Easier and cheaper than a randomized controlled trial (RCT)

•External validity strong compared to RCT

•Can have a longer follow up period compared to RCTs both retrospectively or prospectively

cohort study disadvantages

•Cohorts can be difficult to identify due to confounding variables; role of matching

•No randomization, which means that imbalances in patient characteristics could exist

•Sometimes outcome of interest could take time to occur

•Can have weaker internal validity —more bias to account for…

case control study

compares patients who have a disease or outcome of interest with patients who do not have the disease or outcome, and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.

case control studies are designed to estimate ____ and are ____

odds; observational

case control study advantages

•Good for studying rare conditions or diseases

•Less time needed to conduct the study because the condition or disease has already occurred

•Let's you simultaneously look at multiple risk factors

•Useful as initial studies to establish an association

•Can answer questions that could not be answered through other study designs

case control study disadvantages

•Some retrospective studies have more problems with data quality because they rely on memory and people with a condition will be more motivated to recall risk factors (also called recall bias).

•Not good for evaluating diagnostic tests because it’s already clear that the cases have the condition and the controls do not

•It can be difficult to find a suitable control group that are representative of the target population alongside the cases

cross sectional study

•An observational research method where researchers analyze data from a population at a single, specific point in time.

•Instead of following individuals over time, this approach acts like a "snapshot," comparing different groups within the population to identify correlations between variables

case report

Describes and interprets an individual case, often written in the form of a detailed story

Case reports often describe

–Unique cases that cannot be explained by known diseases or syndromes

–Cases that show an important variation of a disease or condition

–Cases that show unexpected events that may yield new or useful information

–Cases in which one patient has two or more unexpected diseases or disorders

Why are case reports are considered the one of the lowest levels of evidence

–they provide limited evidence for cause and effect/associations

–can be important to identify novel clinical applications or highlight a rare phenomena

systematic review

•A document often written by a panel that provides a comprehensive review of all relevant studies on a particular clinical or health-related topic/question.

•The systematic review is created after reviewing and combining all the information from both published and unpublished studies (focusing on clinical trials of similar treatments) and then summarizing the findings.

systematic review advantages

•Exhaustive review of the current literature and other sources (unpublished studies, ongoing research)

•Less costly to review prior studies than to create a new study

•In general, less time required than conducting a new study

•Results can be generalized and extrapolated into the general population more broadly than individual studies

•More reliable and accurate than individual studies

•Considered an evidence-based resource

systematic review disadvantages

•Very time-consuming

•May not be easy to combine studies due to lack of/inconsistent reporting

meta-analysis

method for systematically combining pertinent qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power. This conclusion is statistically stronger than the analysis of any single study, due to increased numbers of subjects, greater diversity among subjects, or accumulated effects and results

Meta-analysis would be used for the following purposes

–Synthesize findings across multiple studies into a pooled estimate of effect.

–Improve the precision of effect estimates compared to single studies (esp. smaller studies).

–Clarify evidence when studies report inconsistent or conflicting findings.

–Can evaluate benefits, harms, and safety outcomes across a larger body of evidence.

–Explore subgroup effects that may not be detectable in individual studies.

meta-analysis advantages

•Greater statistical power

•Confirmatory data analysis

•Greater ability to extrapolate to general population affected

•Considered an evidence-based resource

meta-analysis disadvantages

•Difficult and time consuming to identify appropriate studies

•Not all studies provide adequate data for inclusion and analysis

•Could require advanced statistical techniques

•Heterogeneity of study populations can be challenging to account for

practice guidelines

A statement produced by a panel of experts that outlines current best practice to inform health care professionals and patients in making clinical decisions

5 steps to EBP process

1.Identify the need for information and develop a question

2.Conduct a search for the best possible evidence

3.Critically appraise the evidence

4.Integrate the evidence with clinical expertise and patient values

5.Evaluate the effectiveness and efficacy of your efforts

EBP pillars are

research evidence, clinical expertise, pt. values

background questions

–General knowledge about disease or intervention

–Foundational knowledge about clinical condition

–Reflect a desire to understand the nature of an individual’s desire or need

foreground questions

–Help you obtain specific knowledge

–Assist in developing diagnosis, prognosis, or plan of care for a specific patient

defining the question: PICO

patient/problem, intervention, comparison/control, outcome