Epidemiology: Types of Studies & Bias

___ bias occurs when historic controls are used as a comparison group for patients undergoing an intervention. Secular trends within the medical system could affect how disease is diagnosed, how treatments are administered, or how preferred outcome measures are obtained. Each of these differences could act as a source of inequality between the historic controls and intervention groups.

Chronology

• ___ bias refers to the fact that researchers and trial sponsors may be unwilling to publish unfavorable results, believing that such findings may negatively reflect on their personal abilities or on the efficacy of their product. Thus, positive results are more likely to be submitted for publication than negative results.

Citation

• ___ occurs when an observed association is due to three factors: the exposure, the outcome of interest, and a third factor which is independently associated with both the outcome of interest and the exposure.

Confounding

Study Types: Experimental ___ Patients in a crossover study will "crossover" to another treatment arm during course of the trial. This means that even if they are initially put into a placebo arm, they will also eventually receive the study drug or standard of care during the trial. Data integrity is ensured by instituting a washout period—a gap in between arms where patients don't receive any medication—in order to reduce carryover effects from the previous treatments.

Cross-over Studies

___ the researcher makes a change or intervenes

Study Types: Experimental In an experimental study, the investigator determines through a controlled process the exposure for each individual (clinical trial) or community (community trial), and then tracks the individuals or communities over time to detect the effects of the exposure. • In experimental studies the researcher makes a change or intervenes and then observes. Randomized Clinical Trials • Crossover Study • Meta-Analysis

Advantages • Greater statistical power • Confirmatory data analysis • Greater ability to extrapolate to general population affected • Considered an evidence-based resource • Disadvantages • 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

Study Types: Experimental Meta-Analysis

Advantages • Better for long term chronic conditions • Fewer patients are needed • All participants will receive the study treatment • Each patient acts as test and control so comparisons are made within the same patient instead of between patients • Disadvantages • Not good short duration or acute conditions • Many participants withdraw from the study • Carryover effects from prior treatments may impact results

Study Types: Experimental Cross-over Studies

Study Types: Experimental ___ combining several selected RCT results would be the highest-level of evidence

Study Types: Experimental Meta-Analysis A subset of systematic reviews; a method for systematically combining pertinent qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power. • Meta-analysis would be used for the following purposes: • To establish statistical significance with studies that have conflicting results • To develop a more correct estimate of effect magnitude • To provide a more complex analysis of harms, safety data, and benefits • To examine subgroups with individual numbers that are not statistically significant • If the individual studies utilized randomized controlled trials (RCT), combining several selected RCT results would be the highest-level of evidence on the evidence hierarchy, followed by systematic reviews,

Study Types: ___ simply observes Emphasis on observing and data collection.

Study Types: Observational • In an observational study, the epidemiologist simply observes the exposure and disease status of each study participant. The two most common types of observational studies are cohort studies and case-control studies; a third type is cross-sectional studies. • Emphasis on observing and data collection.

In almost all clinical studies, subjects are lost to follow-up. In these instances, investigators must consider whether these patients are fundamentally different than those retained in the study. Researchers must also consider how to treat patients lost to follow-up in their analysis. Well designed trials usually have protocols in place to attempt telephone or mail contact for patients who miss clinic appointments. Transfer bias can occur when study cohorts have unequal losses to follow-up.

Transfer bias

___ bias occurs when patient prognostic factors or degree of illness dictates the study cohort into which patients are placed. This bias is more likely in nonrandomized trials when patient assignment to groups is performed by medical personnel. ___ bias is commonly seen in pharmaceutical trials comparing old and new drugs to one another.

Channeling

• In surgical trials, ___ bias may complicate efforts to establish a cause-effect relationship between procedures and outcomes. Variations by surgeon commonly occur in surgical plan, flow of operation, and technical maneuvers used to achieve the desired result.

Performance bias

Advantages • Good randomization will "wash out" any population bias • Easier to blind/mask than observational studies • Results can be analyzed with well known statistical tools • Populations of participating individuals are clearly identified • Disadvantages • Expensive in terms of time and money • Volunteer biases: the population that participates may not be representative of the whole • Does not reveal causation • Loss to follow-up attributed to treatment

Randomized Controlled Trial

Study Types: Experimental ___ Remember that in experimental design you have to have an intervention of some kind. You have to change something and that something has to be able to be evaluated. • Examples of interventions that can be evaluated: • New drugs and new treatment • New medical and health care technology • New methods of primary prevention • New program for screening • New ways of organizing and delivering health service • New behavioral intervention programs.

Randomized Controlled Trial

Study Types: Experimental ___ • A study design that randomly assigns participants into an experimental group or a control group. As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied.

Randomized Controlled Trial

Study Types: Experimental ___ You also must have a comparison group. Examples: • Therapy vs No Therapy • Therapy vs Placebo • Therapy A vs Therapy B • Etc...

Randomized Controlled Trial

Advantages • Good for studying rare conditions or diseases • Less time needed to conduct the study because the condition or disease has already occurred • Lets 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 • Disadvantages • 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

Study Types: Observational Case Control Study

Study Types: Observational ___ compares relationship between the risk factor and the disease. estimate odds

Study Types: Observational Case Control Study • A study that compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls), 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 observational because no intervention is attempted and no attempt is made to alter the course of the disease. The goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls. These studies are designed to estimate odds. • Case control studies are also known as "retrospective studies" and "case-referent studies."

Study Types: Observational ___ • Unique cases important variation unexpected events unexpected diseases or disorders

Study Types: Observational Case Report

• Advantages • Can help in the identification of new trends or diseases • Can help detect new drug side effects and potential uses (adverse or beneficial) • Educational - a way of sharing lessons learned • Identifies rare manifestations of a disease • Disadvantages • Cases may not be generalizable • Not based on systematic studies • Causes or associations may have other explanations • Can be seen as emphasizin

Study Types: Observational Case Report

Study Types: Observational ___ non-diseased people and follows them over time to determine if they develop a disease/outcome. proceeds from cause to effect.

Study Types: Observational Cohort

• Advantages • Subjects in cohorts can be matched, which limits the influence of confounding variables • Standardization of criteria/outcome is possible • Easier and cheaper than a randomized controlled trial (RCT) • Disadvantages • Cohorts can be difficult to identify due to confounding variables • No randomization, which means that imbalances in patient characteristics could exist • Blinding/masking is difficult • Outcome of interest could take time to occur

Study Types: Observational Cohort

• Advantages • Relatively quick and easy to conduct (no long periods of follow-up). • Data on all variables is only collected once. • Able to measure prevalence for all factors under investigation. • Multiple outcomes and exposures can be studied. • The prevalence of disease or other health related characteristics are important in public health for assessing the burden of disease in a specified population and in planning and allocating health resources. • Good for descriptive analyses and for generating hypotheses. • Disadvantages • Difficult to determine whether the outcome followed exposure in time or exposure resulted from the outcome. • Not suitable for studying rare diseases or diseases with a short duration. • As cross-sectional studies measure prevalent rather than incident cases, the data will always reflect determinants of survival as well as etiology. • Unable to measure incidence. • Associations identified may be difficult to interpret. • Susceptible to bias due to low response and misclassification due to recall bias.

Study Types: Observational Cross-Sectional (Ecological) Studies

Study Types: Observational ___ population at a single point in time geographic area

Study Types: Observational Cross-Sectional (Ecological) Studies • A cross-sectional survey is a survey of a population at a single point in time. Surveys may be performed by trained interviewers in people's homes, by telephone interviewers using random-digit dialing, or by mailed, e- mailed, or Web-based questionnaires. • Cross-sectional ecological studies relate the frequency with which some characteristic (e.g., smoking) and some outcome of interest (e.g., lung cancer) occur in the same geographic area.