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Cohort Studies: Producing Evidence for Making Practical Decisions in Librarianship
Mini-Workshop, Evidence-Based Librarianship Conference, Sheffield, UK4 September 2001
Jonathan Eldredge, MLS, PhD
The University of New Mexico Health Sciences Library & Informatics Center
Albuquerque, NM 87131-5686
[email protected] © 2001
A New Technology:
Long Ocean Voyages
A New Problem: Scurvy
• Weakness and Fatigue• Gums itch, swell and easily bleed • Stiffness & feebleness of joints• Edema in legs• Death
Anson’s Circumnavigation of the World
Result:
75% of crew died of scurvy
Research Question:
Does a diet of citrus fruit prevent scurvy in sailors on long voyages?
Three Elements of a Cohort Design
• Population = Sailors on long voyages
• Exposure = Diet including citrus fruit
• Outcome = Prevention of Scurvy
Cohort Design
Copyright 2001 Jonathan Eldredge
Defined Population
What is a “Cohort” ?
1. One of 10 divisions in Roman legion
2. “Band” or “Group”
Source: Webster’s Third International Dictionary. 1993.
Defined Population
“Those people within a geographically or otherwise delineated population who experienced the same significant life event within a given period of time.”
ND Glenn. Cohort Analysis. 1976.
Defined Population
“In epidemiology, the word cohort is often used to designate a group of people who share a common experience or condition.”
Kenneth J. Rothman and Sander Greenland, 1998.
Generic Definition
“A group of subjects selected according to one or more common characteristic(s) and followed over time in order to identify, describe or quantify an event.”
Bernard Bégaud. Dictionary of Pharmacoepidemiology. 2000
Defined Population
Examples from Medicine:• Pregnant women delivering at the Vienna General
Hospital, 1846-1847• Patients with Tuberculosis, 1885-1901• Residents of Hiroshima or Nagasaki, August 1945• Residents of Framingham, MA, 1949-• Vegetarians• Smokers• Female Nurses Aged 30-55 during 1976
Exposure or Non-Exposure• Contact with dead human (cadaveric) tissue• Treatment at the Adirondack Cottage Sanitarium• Ionizing radiation• Lifestyle• Length of vegetarian adherence, alcohol use, Body
Mass Index, tobacco use, exercise, vegan, etc.• Packs smoked per day, years of smoking, etc.• Principally estrogen use, but other lifestyle issues
Cohort Design
Outcome(s)
Hypothesized
Unexpected
None
Cohort Designs
In The Health Sciences
James Lind’s 1747 Cohort Study
Population Exposure Outcome
Sailors on longocean voyages
Diet includescitrus fruit
Prevention ofScurvy
Semmelweis Cohort Study
Population Exposure Outcome
Pregnant womendelivering at theVienna GeneralHospital 1846-47
Dead human(cadaveric) tissue
Greater risk ofChildbed Fever
PCA Louis’ Cohort Study
Population Exposure Outcome
78 cases ofpneumonia, 33
cases of erysipelas(parasites), and 23throat infections
Bleeding Bleeding does notcure these diseases
Recherches sur les effets de la saignée, 1835
Classic Cohort Study
Population Exposure Outcomes
Residents ofHiroshima and
Nagasaki
Ionizing radiationfrom atomic
blasts
Higher incidenceof solid tumors;
retarded growth inyoung
Classic Cohort Study
Population Exposure Outcome
Residents ofFramingham,Massachusetts
(US)
Lifestyle Heart disease
Classic Cohort Study
Population Exposure Outcomes
42,254 women inthe US during the
1970s
Diet of fruit,vegetables, lowfat food, grains
Decreased risk ofmortality
Social Medicine Cohort Study
Population Exposure Outcome
10,609 Swedishcitizens aged 25-74
Regular visits tocinemas, concerts,museums, and artexhibits
Lower mortality
Social Medicine Cohort Study
Population Exposure Outcome
3,617 US citizens LowerSocioeconomic
Status (SES)
Lower SES placesone at higher riskof mortality, evenwhen practicing
healthier behaviors
Humorous Cohort Studies
Population Exposure Outcomes
500 infants, birth to2.5 years old
Presence of “HTVirus”
99% of infantsexperienced
teething
813 Jazz musicians Playing thesaxophone
Higher mortalityrates (“Unsafe
Sax”)
Characters in fourBritish soap operas
TV appearance onone of these shows
Soap operacharacters have the
most dangerousjobs in Britain
Importance of Comparisons
In epidemiology:
“The essential characteristic in the design of cohort studies is the comparison of outcome(s) in an exposed group and a non-exposed group (or a group with a certain characteristic and a group without that characteristic).”
Leon Gordis. Epidemiology. 1996
Importance of Comparisons
Comparisons Made:
• Within the cohort
• With a similar group
Data Collection Approaches:
RetrospectiveSemmelweis in Vienna
ProspectiveJames Lind’s Treatment of Scurvy
The Framingham Study
Potential for Systematic Review
Five Cohort Studies Combined:1. US Adventist mortality
2. UK Health Food Shoppers
3. US Adventist health practices
4. German vegetarians
5. UK Oxford vegetarian studySource: Key TJ, Fraser GE, Thorogood M, Appleby PN et al. Mortality in vegetarians and
nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr 1999 Sep;70(3):516s-24s
Cohort Designs
Outside of the Health Sciences
Cohort Studies in Psychology and Behavioral Sciences
Population Exposure Outcome(s)
Dutch childrenborn 1944-1946
Prenatal famine Psychologicalproblems 1970-
1996
Cohort Studies in Psychology and Behavioral Sciences
Population Exposure Outcome(s)
13,226 Frenchemployees of
companies aged42-56
Varied degrees oflatitude and social
support
Varied levels ofhealth
Cohort Studies in Academe
Population Exposure Outcome
Senior faculty atSyracuse
University inNew York (US)
Tenure Faculty becomemore productiveafter receiving
tenure
Cohort Studies in Sociology
Population Exposure Outcomes
Children raised indysfunctional ordisadvantaged
settings
Differentpersonality traits
Some products ofharsh environments
are remarkablyresilient
Cohort Studies in the Social Sciences
Population Exposure Outcomes
Incoming membersin the US Congress
Politicalexperiences on
Capitol Hill
Reducedpartisanship
Engineers in US1982-1989
Gender Glass CeilingHypothesis
Cohort Studies in the Social Sciences
Population Exposure Outcomes
Sample UKpopulation
Having children Lower family income
Sample USpopulation
News from either TVor newspapers
TV viewers withdeclined verbal
ability
Cohort Studies in Biology
Population Exposure Outcomes
Atlantic Salmon Swimming up riverto spawn
Dramatic weightloss; only 10%return to spawn
again
Cohorts from the Biological or Earth Sciences
• Antarctic seals
• Dogs in the US
• Atlantic Cod
• Evergreen Trees
• Clams
• Fossils of now extinct species
Cohort Studies in Paleontology
Population Exposure Outcome
Fossils ofconodonts
Sea level dropcoupled to
decreased geneticdiversity
Extinction ofconodonts
Cohort Design
Cohort Designs
Examples from Health Sciences Librarianship
Cohort Studies in Librarianship
• Various applications
• More exist than you might think….
Some representative examples
Cohort Studies in Librarianship
General Types:
1. User Population Cohorts
2. Collection or Resources Cohorts
3. Others
Cohort Studies in Librarianship
User Population Cohort Studies
Population Exposure Outcome(s)
Medical students atUniv of Miami
Medline instructionby librarians for
incoming students
Performance onOSCE in 3rd year
90 Pharmacyprogram graduates
from Univ ofMichigan
Online literaturesearch componentof 3rd year course
Extent of database,other information
resource use
Cohort Studies in Librarianship
User Population Cohort Studies
Population Exposure Outcome(s)
Students & graduates ofSchool of Nursing fromUniv Northern Colorado
Information-literacyprogram
Increased confidencewith information-
seeking
Medical, pharmacy, andnursing faculty at UI-
Illinois-Chicago
Enhanced access toelectronic resources
Changes ininformation- seeking
behavior
Cohort Studies in Librarianship
User Population Cohort Studies
Cohort Exposure Outcome(s)
Rural healthcareprofessionals in
Illinois
Outreach programthat included end-
user search training
Use of onlinesearching and
Loansome Doc
Faculty andstudents at the UTHSC San Antonio
campus
Library Publicrelations program
Greater HSCawareness of
library & staffinvolvement
Cohort Studies in Librarianship
Collections or Resources Cohort Studies
Population Exposure Outcome(s)500 consecutiveemail messages
submitted toDigital Health
Sciences Library
Use of DHSL Types ofinformation
requests
1,224 documentdelivery requests
from ruralhealthcare
professionals
Outreach projects Diverse subjectsand 547 journaltitles requested
Cohort Studies in Librarianship
Collections or Resources Cohort Studies
Population Exposure Outcome(s)36,892 books
acquired in 1969 atUniv of Pittsburgh
Availability onshelves
Only 60% booksused after 6 years
1,904 books acquiredduring 6 month
period at DePauwUniv
Availability onshelves
Only 63% of thebooks circulated after
5 years.
Cohort Studies in Librarianship
Collections or Resources Cohort Studies
Population Exposure Outcomes
Books purchasedby 4 medical
libraries published1980-1992
Availability onshelves
79-86% of bookscirculated at 3 sites
2,625 Books added1987-1989 at UI-
Urbana
Availability onshelves
58% bookscirculated
Cohort Studies in Librarianship
Collections or Resources Cohort Studies
Population Exposure Outcome(s)
1,306 books addedduring 1993 atUniv of New
Mexico
Availability onshelves
84% circulated;total 91% usedwithin 4 years
1,958 books added1993-4
Availability onshelves
81% circulatedwithin 3 years
Cohort Studies in Librarianship
Collections or Resources Cohort Studies
Population Exposure Outcomes
194 journal titles atUSC
Both print andelectronic versions
available
Use study in progress
Cohort Studies in Librarianship
Other Types of Cohort Studies
Population Exposure Outcome(s)Monographs
acquired duringyears 1920-1950
Library stacksenvironment
Acidity as the causefor deterioration
Random sample ofMLA members
working inacademic libraries
Professionalincentives ?
Publicationsproduced 1979-
1989 (descriptive)
Cohort Design
Copyright © 2001 Jonathan Eldredge
Question
What other applications of the cohort study design can you think of in librarianship?
Another Question
What kinds of applications of the cohort study design in librarianship can you imagine?
The Cohort Design: A Versatile Tool for EBL Practitioners
Copyright © 2001 by Jon Eldredge, Health Sciences Library & Informatics Center, The University of New Mexico, Albuquerque,
New Mexico USA. All rights reserved.
No portion of this presentation or accompanying handouts may be used or reproduced in any manner whatsoever without written permission of the
author.
Presentation produced in The United States of America