EBM Quiz #2

- tell readers enough about the article so they can decide whether to read it in its entirety

- to identify the focus on the study

-State the purposes of the study or investigation, basic procedures, main findings, and principle conclusions

what are the major purposes of the abstract?

1. If the study has been properly designed and analyzed, would the results be important and worth knowing?

2. if the results are statistically significant, does the magnitude of the change or effect also have clinical significance; if the results are not statistically significant, was the sample size sufficiently large to detect meaningful difference or effect?

- If answers = yes, then it is worthwhile to continue to read

What are the 2 questions you must ask to decide whether to read the article?

intro OR abstract

Where would you discuss the following topics within an article:

- reason for study

- purpose of study

- population included in study

purpose of the study

This is a part of every article that:

- is frequently presented in the last paragraph/sentences of the intro

- should be stated clearly, similar to a 15-second summary of a patient case

purpose of the study

This excerpt was found near the end of the introduction. What is this paragraph stating for an article?

We analyzed whether self-reported exercise tolerance predicts outcomes (hospital length of stay, mortality and morbidity) in PHTN patients undergoing anesthesia and surgery.

info on study's location, length of time, and subjects (realize this could also be in Methods)

Population included in the study is an important part of the research article. What info should this part include?

gives clues to validity of the results

- covers too long of a period, pt entering at the beginning of the study may differ in important ways from those entering at the end

Why is time, usually included in the Population Included in the Study, so important when evaluating a study?

methods section

Part of an article that contains info about how the study was done:

- subjects in the study

- bias related to subject selection

- procedures used in the study and common procedural biases

- assessing study outcomes

- determining an appropriate sample size

- evaluation of the statistical methods

randomized selection/assignment

This type of selection of subjects in the study greatly enhances the generalizability of the results and avoids biases that otherwise may occur in patient selection.

- eligibility criteria (inclusion and exclusion)

- patient followup

- how they were chosen/assigned to treatment

-numbers lost to followup

What are some important things to include in the Subjects in the Study portion of an article?

bias

measurement errors or systematic errors

random error

can occur at any time a sample is selected from a population

- kinda the "opposite" of bias in terms of error

selection bias

easier to control in clinical trials and cohort designs but can occur in any study

prevalence/incidence bias

- occurs when a condition is characterized by early fatalities (some subjects die before being diagnosed) or silent cases (cases in which evidence of exposure disappears when disease begins)

- can result whenever a time gap occurs between exposure & selection of study subjects and the worst cases have died

cohort studies

- case-control studied by limiting eligibility for the study to only newly diagnosed cases

What types of studies are immune to prevalence/incidence bias?

admissions rates bias

occurs when study admission rates differ, which causes major distortions in risk ratios

- Ex: admission rate bias can occur in the studies of hospitalized patients when patients (cases) who have the risk factor are admitted to the hospital more frequently than either the cases without the risk factor or the controls with the risk factors

nonresponse bias or the volunteer effect

bias that occurs when patients either volunteer or refuse to participate in studies

membership bias

essentially a problem of preexisting groups or because 1+ of the same characteristics that cause people to belong the groups are related to the outcome of the interest

membership bias

What type of bias is this example describing?

Investigators have not been able to perform a clinical trial to examine the effects of smoking; some researchers have claimed it is not smoking itself that causes cancer but some other factor that simply happens to be more common in smokers.

procedure selection bias

type of bias that occurs when treatment assignments are made on the basis of certain characteristics of the patients, with the result that the treatment groups are not really similar

- frequently occurs in studies that are not randomized and is especially a problem in studies using historical controls

- Ex; comparison of a surgical vs medical approach to a problem such as coronary artery disease; specifically chose those that were healthier to get the surgery

procedure bias

the most well-known form of bias

- occurs when groups of subjects are not treated in the same manner

- Ex: patients in the treatment group may receive more attention and be followed up more vigorously than those in another group, thus stimulating greater compliance with the treatment regimen

recall bias

type of bias that may occur when patients are asked to recall certain events, and subjects in 1 group are more likely to remember the event than those in the other group

insensitive-measure bias

type of bias in which some measuring instruments may not be able to detect the characteristic of interest of may not be properly calibrated

Ex: routine x-ray films are an insensitive method for detecting osteoporosis because bone loss of approx 30% must occur before xray can detect it; newer techniques are more sensitive and can avoid this type of bias

detection bias

type of bias that can occur because a new diagnostic technique is introduced that is capable of detecting the condition of interest at an earlier stage

- survival for patients diagnosed with the new procedure inappropriately appears to be longer, merely because the condition was diagnosed earlier

- due to new technologies, imaging, labs, etc.

compliance bias

type of bias that occurs when patients find it easier or more pleasant to comply with 1 treatment than another

variability

occurs when the characteristic being measured is a behavioral attribute

- Ex: measurements of functional status

- point out the need for a standardized protocol for data collection

- Ex: always use a manual cuff, always tell patients not to smoke at least 1 hour before taking BP, make sure every collection is taken using the same instrument, etc.

reliability

reproducibility of measurements

- 1 way to establish this is to repeat the measurements at a different time or by a diff person and compare the results

type II error

missing a significant difference in 2 groups is called this type of error

- can occur when the sample size is too small

- "saying nothing is there when it really is" because you didn't evaluate enough people

fishing expedition

the name given to studies in which the investigators do not have clear-cut research questions guiding the research (searching for something)

- problem: capitalizes on chance occurrences and leads to conclusions that may not hold up if the study is replicated

results

Section of an Article:

- includes results of (or findings from) the research directed at questions posed in the intro

- mostly numerical (can present tables or graphs)

1. adequacy of info

2. sufficiency of evidence

What are the 2 major aspects for readers evaluating the results section?

descriptive statistics

found in the results section

- means, standard deviations, risk ratios, etc.

1. authors of medical reports should provide info about the baseline measures of the group involved in the study

2. readers should be alert for the problem of multiple comparisons in studies in which many statistical tests are performed

3. important to watch for inconsistencies between info presented in tables/graphs and the info discussed in the text

What are the 3 characteristics a good results section should have?

- abstract

- intro

- methods

- results

- discussion

- conclusion

What are the 6 parts of a research report we discussed?

discussion and conclusion

Section of an Article: what to watch for in a ________:

-consistency among comments

-questions posed in the intro

-data presented in the results

specificity

The probability of a negative test result in patients who do not have the condition

Sensitivity

The probability of a positive test result in patients who have the condition