8- Research Designs & Critical Appraisal of Literature

Prospective

Follows subjects forward over a specific period of time

Retrospective

-Use historical (previously collected) data from sources such as medical records, insurance claims, or other sources
-Outcome is already known

Cross-sectional

Collects data about a phenomenon during a single point in time or once within a defined time interval

Longitudinal

-Looks at a phenomenon occurring over time
-usually repeated measures at multiple time points

Within-subjects

Repeated measurements are compared for a single group

Between-subjects

Outcomes are compared between two or more independent groups

Randomized control trial

-has a treatment group and a control group; the treatment group receives the treatment under investigation and the control group either receives no treatment, a placebo, or the current standard of care
-reduces selection bias, increases probability that differences between groups are due to the actual intervention and not another factor

Advantages of randomized control trial

-Elimination of extraneous variables
-Controls
-Reduces bias (both known and unknown)

Blind study

participants are not told whether they're in the control or experiment group

Cohort studies

A group of individuals in a study who are followed over a period of time; often the group is defined by a particular characteristic, such as age

Cohort (longitudinal) is used to ___________

establish causation of a disease or to evaluate the outcome/impact of treatment when randomized controlled clinical trials are not possible

Advantages of cohort study

-allows study of subgroups for whom it would not be ethical to allocate to treatment groups in an RCT
-Often richer, more comprehensive data

Disadvantages of cohort study

-Can be difficult to identify rarer or uncommon patient presentations, would be underpowered
-Comparing treatment groups can be challenging

Case-control studies

-Used to compare two groups of people, patients with the condition and ones without (control)
-can determine if there is a relationship between a certain factor and the condition

Case report/study or case series

-single report or collection of reports on the treatment of patients with the same condition
-used to generate ideas for a bigger study

Benefits of case report/series

-easy to understand
-can be useful for conditions/situations where there is little evidence

Drawbacks of case report/series

-Limited to no statistical validity
-No control for bias, only interesting/positive results tend to be published

Systematic review

a collection of individual research studies is gathered and critically appraised in an effort to reach an unbiased conclusion about the cumulative weight of the evidence on a particular topic aka syntheses

order of reliability of studies

1) systematic review, meta-analysis

2) randomized control trials

3) cohort studies

4) case control studies

5) cross-sectional studies

6) case studies

meta-analysis

-A statistical method used to pool data from individual studies in a systematic review
-easier when interventions and outcomes of included studies are similar
-increases power since sample size increases

Review articles (non-systematic)

-Summarizes the current state of understanding on a topic; focuses on the current state of the scientific literature on a specific area of science rather than an experiment

Contents of a review article

Important people in the field, major discoveries, unanswered questions, ambiguities/debates, future directions of research

internal validity

-The extent to which the results represent the truth in the population we are studying vs. methodological errors
-Did the study do things right?
-Do we trust the results?

External validity

-The degree to which the findings of a study can be applied to other situations, people, or contexts—how generalizable are the results
-Environment, patient population, income, how healthy they are

Introduction

-Provides background, rationale for the study, what it contributes to current knowledge
-The "why" for the article

Research Article: Methods

-describes what was done: devices used for measurement, study design, participants
-Includes: subjects, data analysis, statistics—any important info on how the study was conducted

Results

What the researchers found, including graphs and figures to illustrate major findings

Discussion

Authors discuss their results, what they may mean, and any limitations or future questions that arose because

Conclusion

Summary statements

References

detailed description of the source of information that you want to give credit to via a citation

CONSORT

Used to evaluate clinical trials

STROBE

Used to evaluate cohort studies/cross sectional studies

PRISMA

Used to evaluate systematic reviews

SQUIRE

Used to evaluate quality improvement studies

Exclusion criteria

-characteristics of elements that will not be included in the sample
-Study ineligibility
-Specify extraneous factors that are anticipated to influence the outcome of

Inclusion criteria

-characteristics that each element must possess to be included in the sample
-Study eligibility
-Broad enough to maximize sample size
-Narrow enough to minimize extraneous influence

Sample size

Number of observations in a sample

Power

The ability to detect a difference (or a relationship) in a study if one exists

Larger samples tend to be ______ representative of the population than smaller samples

more

Non-probabilistic sampling

• Methods for choosing subjects that do not use a random selection process; as a result, the sample may not represent accurately the population from which it is drawn

• More feasible: easier to implement and costs less

• Good with conditions for which sample size would be too small to do random methods

• Increase chance for sampling error

Convenience sampling

choosing individuals who are easiest to reach

Snowball sampling

recruitment of participants based on word of mouth or referrals from other participants

Probabilistic sampling

-random selection process to increase the chance of obtaining a sample that accurately represents the population from which it is drawn
-Minimizes investigator bias

Simple random sampling

every member of the population has an equal probability of being selected for the sample

Systematic sampling

procedure in which the selected sampling units are spaced regularly throughout the population, every n'th unit is selected

Stratified random sampling

technique in which the researcher identifies particular demographic categories of interest and then randomly selects individuals within each category

Cluster sampling

A probability sampling technique in which clusters of participants within the population of interest are selected at random, followed by data collection from all individuals in each cluster.

Accessible population

Potential subjects who are available for study

blinded assessor

-individual who evaluates the outcomes without knowing which treatment or intervention the participants received
-prevent observer bias