Tag Archives: research article

Cohort & Case-controlled studies: Going forward & backward

Got a clinical problem?  You probably want to solve it with evidence—STRONG evidence.   Click on this link to see one well-accepted hierarchy from strongest #1 to weakest #7 (Melnyk & Fineout-Overholt, 2005).   Today let’s look at the 4th strongest level of evidence = Case controlled or cohort studies

First a quick review

Click here for a quick review of the strongest 2 levels of evidence (#1 Systematic reviews, Meta-analyses, or Evidence-based clinical practice guidelines based on systematic review of RCTs. #2 Randomized controlled trials)

Click here for a review of the 3rd strongest type of evidence (#3Controlled trials without randomization)

Now on to the new “stuff”  strong

All 3 of the top, strongest levels of evidence are experimental studies (or include available experimental studies). That means the researcher actually does something or gives a treatment to some of the subjects and then records the outcomes. 

The weaker 4 levels of evidence are non-experimental designs. This means that the researcher merely observes & does Not do anything to subjects. So how does that work?!

First, a cohort study (non-experimental). A cohort study starts with a group of people who have something in common and then the researcher observes only & keeps collecting data from them over a long time into the future. Data collection into the future is called a prospective study. An example is the Nurses’ Health Study, in which over 20,000 nurses were identified and followed-up annually with tests and surveys for over 25 years (this study is still ongoing). These studies provide very valuable information, but are obviously very expensive and time-consuming.”(OMERAD EBM course, 2008)

Now a case-controlled study (non-experimental).  In a case controlled study the researcher observes only & collects data over time into the past (not the future). Data collection into the past is called a imagesCAH6C8NTretrospective study. Again, from the OMERAD EBM (2008) site this example: “Patients with a disease are identified who have suffered a bad outcome such as death or recurrence, and compared with patients who have the disease but haven’t suffered the bad outcome. For example, a researcher might  identify a group of breast cancer patients who have died…, and compare them with a similar group of patients with breast cancer who are still living.”

Critical thinking: Which of these would be better for casQUESTIONe-controlled study and which for cohort study.

  1. You are a runner in the Los Angeles marathon and you are interested in how that race can improve cardiovascular health among those who finish. Question: Cohort or Case controlled?
  2. Some finishers of the LA marathon die of heart attacks 20 years later; many survive another 40 years.   Question: Cohort or Case controlled?

For more info see:


“I like my coffee (and my evidence) strong!”

Let’s say you are still working to solve the issue of whether gum chewing reduces post-operative ileus. You identified titles of all relevant articles using PubMed database (http://www.ncbi.nlm.nih.gov/pubmed), and had the librarian pull the full articles for you.

Now you find yourself looking at a formidable stack of articles on the topic. You are sure that some are probably better quality than coffee2others, but how can you tell?

Professionals have agreed on which types of evidence are strongest. Here’s one well-accepted hierarchy form strongest #1 to weakest #6 (Melnyk & Fineout-Overholt, 2005).

  1. Systematic reviews, Meta-analyses, or Evidence-based clinical practice guidelines based on systematic review of RCTs
  2. Randomized controlled trial
  3. Controlled trials without randomization
  4. Case controlled or cohort studies
  5. Systematic review of descriptive studies
  6. Single descriptive or qualitative study
  7. Expert opinion of individuals or committees

Number 1= Strongest.   Number 6=Weakest

When you are trying to solve a problem, FIRST look for the three (3) types of evidence that are the very strongest (#1). These are:

  1. Systematic reviews that are summaries of research findings from many studies;
  2. Meta-analyses that are summaries of research findings in which the data from those other studies are combined into one big study;
  3. Evidence-based clinical practice guidelines that are clinical recommendations based on a summary of research and other evidence. An expert panel has often agreed on the summary and recommendations.

Your next strongest option, #2, is at least one randomized controlled trial (RCT). In an RCT a group of subjects is randomly separated into at least two groups. One group gets the experimental treatment—whether it is a drug or teaching plan or something else—and the other group usually gets standard treatment or a placebo. Then the group outcomes are compared statistically to see which did better.

Usually the title or first few lines of the article will tell you that the article is a systematic review, a meta-analysis, an evidence-based clinical practice guideline, or an RCT. Rarely is this left a mystery! (Never assume that a research study article is strong just because you LIKE the findings, or that it is weak because you DON’T like the findings.)

I’ll comment on other levels of evidence soon, but let’s focus on the strongest types first. Try the critical thinking for practicing the ideas above.

Critical Thinking:  Using the article titles below, rank these three (3) research studies in order from Strongest evidence to Weakest evidence:

Want to read more?  A good summary of one hierarchy is and why it’s important is at this 5 minute youtube video: https://www.youtube.com/watch?v=5H8w68sr0u8 . While that hierarchy does not precisely match the one above, the video still has lots of good information.



“Take 5!” (minutes to learn about 4 search strategies)

“TAKE 5” minutes to learn about 4 best strategies to find nursing research articles. Watch the video at this link: https://www.youtube.com/watch?v=Em7b9jr-ZK8&list=PLQKD1cO-QY3Rt2PaLd3dykeL4HZo7mCZv&index=7

(Well it’s technically 5:23 minutes, but as with calories, who’s counting?)

A great place to use these 4 strategies is the highly comprehensive and reliable PubMed database. You already pay for that publicly available healthcare research database with your tax dollars, so go to http://www.ncbi.nlm.nih.gov/pubmed/ and get your money’s worth!   PubMed even has a link to show you how to use those 4 strategies specifically on PubMed. (Check that out at http://www.nlm.nih.gov/bsd/disted/pubmedtutorial/020_340.html)

One of your search terms can be nurs* if you want a better chance of finding only nursing articles. You’ll know what that little asterisk means after you “TAKE 5!” with the first video link.

Some PubMed articles are free for you to print or save. Many are not. That means you will need to take the list of articles that you found in your search to your hospital librarian for help. OR if you have access to library databases through a school you can find full text of most articles there or order them through interlibrary loan.

If you don’t have access to library databases yourself, here’s a good way to work with a hospital librarian.

  1. Use the 4 search strategies to find relevant articles on PubMed.
  2. Give that list of articles to your librarian who is likely to have a budget and time to pull the full articles for you.
  3. If you find only one article that fits the problem you are trying to solve, you can take that article to the librarian and ask the person to find you more like that one.

Another public database is Google Scholar, but it is not as accurate or thorough. For its strengths and weaknesses and how to use it well, you might find this handout useful (https://www.dit.ie/media/library/documents/kevinst/Guide%20How%20to%20use%20Google%20Scholar.pdf).

Happy evidence hunting!

“It’s All in The Name!” Titles of Research Articles

Research articles have relatively standardized sections:

• Title 
• Abstract (overview of project that is somewhat incomplete)
• Introduction (purpose, problem, & background)
• Methods (sample, setting, measurements collected)
• Results (data analysis from measurements), &
• Discussion/conclusions (what the data analysis tells us about the original purpose & problem)
These may vary a little from article to article.

Let’s look at the TITLE for a minute. A good title is a mini-abstract. A good title will include:
• Key variables (remember a variable is something that varies, such as fatigue or satisfaction)
• Population studied
• Setting of study
• Design of study

For example take this research article title “What patients with abdominal pain expect about pain relief in the Emergency Department” by Yee et al in 2006 in JEN.
• Key thing that varies? Expectations about pain relief
• Population studied? ED patients with abdominal pain
• Setting? May be the ED
• Design? (not included, but those with experience in reading research would guess that it is probably a descriptive study—in other words it just describes the patients’ expectations without any intervention.)

There you have it! Now you know about TITLES!!