evidence based medicine quiz 1

biostatistics

the application of statistics in the heath related fields

epidemiology

the study of health and illness in human populations, or the patterns of health and disease and the factors that influence these patterns

evidence-based medicine

once we now the epidemiology of a disease, it is used to understand the cause of the disease, determine public health policy, and plan treatment

intervention

an investigator-controlled maneuver, such as a drug, a procedure, or a treatment

retrospective study

the nature of the inquiry is backward in time

prospective study

look forward in time

longitudinal study

the inquiry covers a period of time

case (experimental group)

individuals selected on the basis of some disease or outcome

control (control group)

individuals without the disease or outcome

cohort

a group of people who have something in common & who remain part of a group over an extended time

clinical trial

experimental studies in medicine that involve humans

controlled trial

studies in which the experimental drug or procedure is compared with another drug or procedure, sometimes a placebo and sometimes the previously accepted treatment

uncontrolled trial

studies in which the investigators' experience with the experimental drug or procedure is described, but the treatment is not compared with another treatment, at least not formally

concurrent control

to plan interventions for both groups for the same time period in the same study

double-blind trial

neither subjects nor investigators know whether the subject is in the treatment or the control greoup

blind trial

when only the subject is unaware, but researcher knows which group they belong to

hawthorne effect

people change their behavior and sometimes improve simply because they receive special attention by being in a study and not because of the study intervention

crossover study

two group of patients: one group is assigned the experimental treatment and the second group is assigned the placebo or control. after a time, the experimental treatment and placebo are withdrawn from both groups for a washout period. The groups then switch.

historical control

the controls are patients the investigator has previously treated in another manner, external to this study

meta-analysis

uses published information from other studies and combines the results so as to permit to an overall conclusion

representative (of a population)

a sample that accurately reflects the characteristics of the population as a whole

qualitative

data on a nominal scale, describes a quality of the person or thing studied

quantitative

the differences between numbers have meaning on a numerical scale, measures the quantity of something

rank order scale

observations are ranked from highest to lowest

mean

average of the observations

median

middle observation

mode

the value that occurs most frequently

bimodal

when the set of data has two modes

range

the difference between the largest and smallest observation

standard deviation

a measure of the spread of data about their mean

percentile

the percentage of a distribution that is equal to or below a particular number

interquartile range

the difference between the 25th and 75th percentile

frequency table

used to display quantitative data, show frequency in each category, and often percentiles

histogram

present the measure of interest along the X-axis and the number or percentage of observations along the y-axis

box plot

used to illustrate certain locations in the distribution

frequency polygon

line graphs similar to histograms, useful when comparing two distributions on the same graph

proportion

the number of observations with a given characteristic (A) divided by the total number of observations in a given group (A + B)

proportion = A/(A+B)

percentage

proportion multiplied by 100

ratio

the number of observations in a group with a given characteristic divided by the number of observations without the given characteristic

rate

similar to proportions, except that a multiplier is used, and they are computed over a specified period of time

mortality rate

provide a standard way to compare number of deaths occurring in different populations, deaths due to different diseases in the same population, or deaths at different periods of time

morbidity rate

number of individuals who develop a disease in a given period of time divided by the number of people in the population at risk

prevalence

the number of individuals with a given disease at a given point in time divided by the population at risk for that disease at that time

incidence

the number of new cases that have occurred during a given interval of time divided by the population at risk at the beginning of the time interval

contigency table

observations are classified according to several factors, used when two characteristics on a nominal scale are examined

bar chart

counts or percentages are shown in bars

correlation coefficient

one measure of the relationship between two numerical characteristics, symbolized by X and Y

spearman rank correlation

aka Spearman's rho; used to describe the relationship between two ordinal characteristics

relative risk

ratio of the incidence in people with the risk factor (exposed people) to the incidence in people without the risk factor (non-exposed people)

odds ratio

the odds that a person with an adverse outcome was risk divided by the odds that a person without an adverse outcome was at risk

absolute risk reduction

provides a way to assess the reduction in risk compared with the baseline risk

number needed to treat

in order to prevent one event

scatterplot

used to illustrate the relationship between two characteristics when both are measured on a numerical scale

when do you use a case-series study?

to track a small group of patients with a similar condition or treatment

what is the research question of a case-series study?

the author describes some interesting or intriguing observations that occurred for a small number of patients

how is the study set up for a case-series study?

not usually planned and do not involve any research hypotheses

who are the participants of case-series study?

small number of patients who share a similar disease, exposure, or clinical outcome

what type of data is obtained for a case-series study?

descriptive, observational date (usually both qualitative and quantitative)

how do you record the data in a case series study

tracking the clinical histories, treatments, and outcomes for a group of patients with a similar conditino

advantages of case-series study?

- they are easy to write

- the observations may be extremely useful to investigators designing a study to evaluate causes or explanations of the observations

disadvantages of case-series study?

- susceptible to many possible biases related to subject selection and characteristics observed

- in general, you should view them as hypothesis-generating and not as conclusive

When do you use case control studies?

when you begin with the absence or presence of an outcome and then look backward in time to try to detect possible causes or risk factors that may have been suggested in a case-series report

what is the research question in case-control study?

whether a specific exposure is associated with a particular health outcome or disease

how is the study set up in case control studies?

subjects in the study are chosen at the onset of the study after they are known to be either cases with the disease or outcome or controls without the disease or outcome

who are the participants in the case control studies?

divided into two distinct groups based entirely on whether or not they currently have the health outcome being studied

what type of data is obtained in the case control studies?

they obtain retrospective exposure and demographic data

how do they record data in the case control studies?

could be through interviews and questionnaires, medical records, and biological samples

advantages of case control studies?

- appropriate for studying rare diseases or events, for examining conditions that develop over a long time, and for investigating a preliminary hypothesis

- quickest and least expensive studies to undertake and are ideal for investigators who need to obtain some preliminary data prior to writing a proposal for a more complete, expensive and time-consuming study

disadvantages of a case control study?

- largest number of possible biases or errors, and they depend completely on high-quality existing records. Data availability for case control studies sometimes requires compromises between what research wish to study and what they are able to study

- selection of an appropriate control group. the cases in a case control study are relatively easy to identify, but deciding on a group of persons who provide a relevant comparison is more difficult

when do you use cross sectional studies?

to observe a population at a single point in time

what is the research question of a cross sectional study?

measuring the prevalence of a condition or identifying associations between variables at a single, specific point in time

how is the study set up in a cross sectional study?

analyze data collected on a group of subjects at one time rather than over a period of time

who are the participants of a cross sectional study?

individuals drawn from a specific population of interest at a single point in time

what type of data is obtained in a cross sectional study?

observational data at a single point in time

how do you record the data in a cross sectional study?

taking a snapshot of a population to measure exposures and outcomes at the same specific point in time

advantages of a cross sectional study?

- best for determining the status quo of a disease or condition, such as the prevalence of HIV in given populations, and for evaluating diagnostic procedures

- relatively quick to complete, and they may be relatively inexpensive as well

disadvantages of a cross section study?

- provide only a snapshot of time of the disease or process, which may result in misleading information if the research question is really one of disease process

- obtaining sufficiently large response rates; many people asked to participate in a survey decline because they are busy, not interested and so forth. The conclusions are, therefore, based on a subset of people who agree to participate, and these people may not be representative of or similar to the entire population

When do you use a cohort study?

when you ask a question looking forward in time

what is the research question of a cohort study?

whether a specific exposure increases or decreases the risk of a certain outcome over a set period of time

how is the study set up of a cohort study?

tracks a group of similar people over time to see how their exposures affect their likelihood of developing specific outcomes

Who are the participants in a cohort study?

a group of people who have something in common and who remain part of a group over an extended time

what type of data is obtained in a cohort study?

exposure and outcome data

how do you record the data of a cohort study?

developing a structured date dictionary and using a secure database to track variable, exposures, and outcomes over time

advantages of a cohort study?

they establish a clear temporal sequence - proving that an exposure occurred before the outcome developed

disadvantages of cohort study?

high costs, long timeframes, vulnerability to participant dropout, and inefficiency in studying rare disease

what are controlled trials?

studies in which the experimental drug or procedure is compared with another drug or procedure, sometimes a placebo and sometimes the previously accepted treatment

what are randomized controlled trials?

the epitome of all research designs because it provides the strongest evidence for concluding causation

what are nonrandomized trials?

studies that do not use randomized assignment

opened to many sources of bias, so their conclusions are highly questionable

what are trials with self-controls?

- Use the same group of subjects for both the experimental and control options

- "Before and after"

- Vulnerable to the Hawthorne effect

what are trials with external controls?

- Compare to the results of another investigator's research, or patients the same investigator has previously treated in another manner (historical controls)

- Often used to study diseases for which cures do not yet exist

- Must consider whether other factors may have changed since the time the historical controls were treated

what are uncontrolled studies?

a study involving interventions have controls, and by strict definition they are not really experiments or trials

what happens in a phase I trial?

Tests the drug in a few people for safety and adverse reactions and ascertains safe and unsafe doses (non-therapeutic).

- already researched for a while

- purpose is to determine basic safety, pharmacokinetic, and pharmalogic information

what happens in a phase II trial?

range from small, single-arm studies to randomized trials comparing a control treatment with the experimental drug in either a single dose or at several doses

- study subjects are the patient population that has the disorder of interest

what happens in a phase III trial?

-large clinical studies that can involve the treatment of several hundred subjects from multiple centers with a goal of assessing therapeutic benefit

- large number of patients allow for the development of a broad database of information about saftey and efficacy

- includes fixed dose studies, flexible dose studies, and studies that include the comparison of a gold standard treatment alnog with the experimental agent and placebo

- pivotal studies that will serve as the basis for FDA approval

what are phase IV clincal trials?

-initiated after a drug has been approved by the FDA

-postmarketing studies

nominal scales

name scale

used for the simplest level of measurement when data values fit into categories

it isnt measured, we count the number of observations with or without the attribute

ordinal scales

one is better than the other

observations are still classified, but are placed in order or more than or less than

used to determine a patient's amount of risk or the appropriate type of therapy

numerical scales

the differences between numbers have meaning on a numerical scale, measures the quantity of something

frequently displayed in a variety of tables and graphs

means and standard deviation are used to summarize the values