Freshmen Flashcards by Cal Schiller

Observes associations

Show patterns of disease occurrence

Helps to generate hypotheses

Descriptive Research

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Analyzes associations

Investigates relationships

Tests hypotheses

Analytic Research

or explanatory

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_____ epidemiologic studies reveal the patterns of disease occurrence in human populations

Descriptive

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Provide general observations concerning the relationship of disease to basic characteristics.

Person
Place
Time

descriptive

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Descriptive studies examples

case reports

clinical series

populations (ecologic studies)

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Attempt to provide insight into etiology or find/ determine better patient outcomes:

Explanatory Studies

analytic

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Has an active intervention from the investigator.

Examples:
Controlled trial
Clinical trial
Educational intervention
Healthcare trial
Intervention trial

experimental

descriptive

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Investigator observes nature.

Examples:
Case-control
Follow-up
Cross-sectional
Cohort or follow up

observational

descriptive

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A narrative in the professional literature that identifies a single incident and discusses pertinent factors related to the patient

Case Report

Information is preliminary and unrefined in terms of research methodology

(descriptive)

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this type of study analyzes a number of individual cases that share a commonality

case series

descriptive

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Examine adverse events or effects

Catalog new diseases or outbreaks

Determine the feasibility or safety of a new treatment or intervention

Discuss the potential efficacy of a new treatment

Case series

descriptive

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Case reports and case series lack

“sufficient methodological rigor”

Data does not necessarily extrapolate to larger populations

Evidence may be circumstantial

Confounding factors may be present

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both typically indicate the need for further study

Case reports and case series

descriptive

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Examine the relationship between exposures and diseases as measured in a population rather than in individuals.

Ecologic studies

descriptive

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Is a type of bias specific to ecological studies. Occurs when relationships that exist for groups are assumed to also be true for individuals

Ecological Fallacy

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After describing an association at the population level, the next step would be to do a an analytic study to see if the association holds true in individuals.

Ecologic studies

descriptive

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Examines the relationship between outcomes and other variables of interest as they exist in a defined population at one particular time

cross sectional study

Observational-Explanatory

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Determines prevalence (% of population) not incidence (rate)

cross sectional study

Observational-Explanatory

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cannot show causality, does not separate cause/effect

cross sectional study

Observational-Explanatory

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Does not establish a temporal relationship between risk factors and disease because they are measured at the same time

cross sectional study

Observational-Explanatory

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cross sectional study strengths:

Observational-Explanatory

Can assess multiple outcomes and exposures simultaneously

Can be completed quickly

Data generated can lead to further studies

Can generate prevalence

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cross sectional study limitations:

Observational-Explanatory

No time reference

Only useful for common conditions

Cannot calculate incidence, it is a prevalence study

Results are dependent on the study population

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Studies in which patients who already have a specific condition (cases) are compared with people who do not have the condition (controls).

The researcher looks back to identify factors or exposures that might be associated with the illness

Case control study

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This type of study design may follow a case-series (as a retrospective look at causes).

Tries to capture the cause and effect relationship by comparing frequency of a risk factor among those how are exposed and not-exposed.

Case-control studies

an observational study

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Case control strengths

GOOD FOR STUDYING RARE OUTCOMES Can evaluate many exposures Ideal for initial/explanatory idea simple/fast INEXPENSIVE

Case control limitations

single outcome high risk for bias high for confounding variables other factors exist that influence outcome can't determine prevalence temporality

Can’t make causal interpretations Can’t determine incidence Can’t calculate Relative risk

temporality

A third variable that has an effect on the outcome but not causal E.g., alcohol associated with lung cancer but so is smoking

confounding variables

inappropriate selection of cases or controls

selection bias

Can be selected from a variety of sources: Hospitals, Clinics, Registries. If cases are selected from a single source, and risk factors from that facility may not be _____ to all patients with that disease

generalizable | Cases-selection bias

Ideally, you want ____ to come from the same reference population that cases are derived from. An inappropriate control group can have the opposite effect and obscure an important link between disease and its cause

Controls | could be a form of selection bias if control aren't accurate representations

Occurs when there is a differential recall of exposure between cases and controls

Recall bias | main form of information bias

Occurs when the researcher/observer evaluates cases vs controls differentially

Researcher/Observer Bias

Arises when case subjects who think they have been exposed to responds at a higher rate to controls.

Voluntary Reponses Bias

Process of selecting the controls so they are similar to the cases in certain characteristics, such as age, race, sex, socioeconomic status, and occupation (control bias)

Matching

For each case selected for the study, a control is selected who is similar to the case in terms of the specific variable (matching type, control bias)

individual

Select controls with a certain characteristic that is identical to the proportion of cases with same characteristic (matching type, control bias)

group-based

Problems with matching:

If you select too many matching characteristics it is difficulty to find an appropriate control You lose the ability to study a matched variable

Employ multiple control groups which offers independent estimates of exposure among different samples of non-cases. Increases strength of the study

Multiple controls

Other Types of Case-Control Studies

Case-crossover Nested Case-Control Case-Cohort

A variant of a case-control study Each case becomes their own individual control Used for transient exposures during a discrete occurrence

Case crossover (air pollution is a typical metric that uses case crossover) (slide 32 Analytic Study Design Pt. 1)

A case control study within a large cohort Typically seen with large enrollment studies Controls are a sample of individuals who are at risk for the disease/outcome at the TIME each case of the disease develops

Nested Case-Control | slide 30 in Analytic Study Design Pt. 1

Same as nested case-control design, expcet controls are randomly chosen from the cohort at the beginning of the study.

Case cohort | slide 31 in Analytic Study Design Pt. 1

a group of people who share a common characteristic or experience and all remain in the group for a period of time

cohort

an epidemiologic investigation that follows groups with common characteristics, strongest observational study

cohort study

identify a group of patients who are already taking a particular treatment or have an exposure, follow them forward over time, and then compare their outcomes with a similar group that has not been affected by the treatment or exposure being studied (type of cohort study)

prospective best observational for addressing a causal relationship follow-up is same as cohort study

start with a cohort and go back in time to evaluate past exposures to risk factors (type of cohort study)

Retrospective | similar to case-control in that it's retrospective

People with disease are selectively lost to follow-up, and those lost to follow-up differ from those not lost to follow-up (selection bias in cohort studies)

"lost to follow up"

Quality and extent of information is different for exposed person than for non-exposed person, a significant bias can be introduced. (information bias in cohort bias)

Information bias

Occurs when the observer decides whether the disease has developed in each subject also knows whether that subject was exposed. (information bias in cohort bias)

Observer Bias | leading questions, etc.

Cohort strengths

may study multiple effects of single exposure Can identify a temporal relationship between exposure and disease (outcome) Help confirm cause and effect of disease and the magnitude of the effect Can measure incidence (rate) of disease Can calculate Relative Risk Highest validity of observational study design

Cohort studies limitations

Expensive and time consuming Inefficient for studying rare diseases Lose participants to follow-up Risk of confounding variables Retrospective studies require presence of records or recall

What point should cohort be identified (or when does the diagnosis begin/how far to "go back")? Attempt to make cohort representative of national population? How long should cohort be followed? What hypothesis/how many to test?

Consideration for cohort study

Start with exposure, look for disease Prospective/Retrospective Common diseases High risk for dropout

Cohort study

start wtih disease retrospective rare disease recall/selection bias

case-control study

It’s important to read articles and be concerned for “bias that _____”

has not been addressed

May be done by assigning random numbers or by a program that generates random assignments Each subject has an equal chance of being assigned to each group (control or intervention) Randomization strives for comparability of the different treatment groups; however, its not guaranteed

Randomized control studies

The main purpose of randomization is to prevent any potential biases on the part of the investigators from the influencing the assignment of participants into different treatment groups

Randomized control studies

*The main purpose of randomization is to prevent _____

any potential biases on the part of the investigators

For randomized controls studies, controlled implies predefined:

Specified hypotheses Primary and secondary endpoints to address hypotheses Methods for enrollment and follow up Eligibility/Exclusionary criteria Rigorous monitoring Analysis plans and stopping rules

Criteria for determining selection must be specified *before the study is begun*. Want to ensure that participants actually have the disease of interest. Carefully select sample based on reference ____. (enrollment in randomized control) studies)

population

If allocation is conducted properly we don’t have to worry that any subjective biases of the investigator, either overt or covert, may be in introduced into the process of selecting patients.

(enrollment in randomized control)

Randomization is accomplished by?

Computer programs Envelope system

Envelope is only opened after a subject is consented & MEETS ELIGIBILITY CRITERIA

envelope system | randomization

utilized when we are concerned about the comparability of the groups in terms of one or a few important characteristics. This is conducted by stratifying our study population by each variable that we consider important, and then randomize participants to treatment groups within each stratum

Stratified Randomization

The concealment of group allocation from one or more individuals involved in a clinical research study. Usually is used in research studies that compare two or more types of interventions.

Blinding | Randomized control studies

Blinding used to make sure that knowing the type of treatment does not affect:

A participant's response to the treatment A health care provider's behavior The assessment of the treatment effects

After being observed for a certain period of time on one therapy; any changes are measured; patients are switched to the other therapy. Each patient can serve as his or her own control, holding constant the variation between individuals in many characteristics that could potentially affect a comparison of effectiveness of two agents. Must have a washout period!

Planned Crossover

Occurs when subjects who are randomized cross-over to the other group. If we analyze according to treatment that the patient actually receive, we will have broken and therefore lost the benefits of randomization. Current practice to perform the analysis by intention to treat-according to the original randomized assignment. If bias occurs typically biases towards the null; typically provides a more conservative estimate

Unplanned crossover

intention to treat

even if case doesn't follow tx, they perform analysis by the original randomized assignment

Allocation is concealed from only one group (researchers or subjects)

Single blinding

Allocation is concealed from both groups (researchers and subjects)

Double blinding

Allocation is unknown to the subjects, the individuals who administer the treatment or intervention, and the individuals who assess the outcomes.

Triple blinding

the Gold-standard

Double-blinded Randomized Control Trial Minimizes the chance for bias if randomization and blinding are done correctly

``` Large trials (may affect statistical power) Long term follow-up (possible losses) Compliance Expensive Possible ethical questions Primum Non Nocere / ‘First Do No Harm’ ```

Randomized control studies limitations

Attempted to learn if the drug, surgical procedure, or administrative program works under ideal circumstance

Efficacy Trial

Within the confines of the study, results appear to be accurate and the interpretation of the investigators I supported

Internal Validity

Ability to apply results obtained from a study population to a broader population. Also called generalizability

External Validity

In non-randomized controlled trials, the control group is predetermined (without random assignment) and compared to a control group Volunteer to join the study OR Are geographically close to the study site OR Conveniently turn up (at a clinic, school) while the study is being conducted Like the studies recruiting with fliers posted in the restroom

Non-randomized control studies

Enrollment – How was the study population chosen? Allocation – How were the subjects assigned to their study group? Follow Up – How long are patients followed for? Analysis – How was the data collected analyzed?

Four major areas of methodological concern for Randomized and Non-randomized control studies

What were the inclusion and exclusion criteria? Is the actual study population representative of the population to which the results will be applied? Are controls similar to case subjects?

enrollment

``` Was randomization and blinding conducted? How was it done? Was it done correctly? Nonrandom sampling (consecutive or convenience) may not be generalizable and has strong potential for bias ```

Allocation

Adherence How well did the study subjects adhere to the treatment protocol? Was the intervention too difficult to continue to participate? Attrition How many subjects were lost to follow-up? Why were they lost? Did they quit or die?

Follow Up

Are the effects of the intervention clearly defined? Is there a clearly defined end point? Did they provide an “intent to treat” analysis? Compares subject outcomes based on their original group assignment even if they dropped out or were non-compliant Primary reason is to preserve randomization To what did they compare their data?

Analysis

Takes the results of a large numbers of primary research studies and combines them into one Synthesis a great deal of research!

Systematic Reviews and Meta-analyses

The top two levels of the EBM pyramid

Systematic Reviews and Meta-analyses

A “systematic review” is a thorough, comprehensive, and explicit way of interpreting the medical literature A "meta-analysis" is a statistical approach to combine the data derived from several selected studies

the difference between a "systematic review" and a "meta-analysis" Both are used for the development of Clinical Practice Guidelines (CPGs)

A method for combining pertinent study data from several selected studies that are similar enough to justify a quantitative summary to develop a single conclusion that has greater statistical power

Meta-analyses A statistical synthesis of the numerical results of several trials which all addressed the same research question

The conclusion is statistically stronger than any single study due to:

increased numbers of subjects greater diversity among subjects accumulated effects and results

Greater statistical power Confirmatory data analysis Greater ability to extrapolate to the general population

Meta-analyses Strengths

Difficult and time consuming to identify appropriate studies Not all studies provide adequate data for inclusion and analysis Requires advanced statistical techniques Heterogeneity of study populations Age, gender, etc. Results are not always reproducible by other investigators Subject publication Bias, Selection Bias, and Misclassification Bias Can give a false sense of certantiy regarding the magnitude of risk

Meta-analyses Limitations