Cohort Studies: Producing Evidence for Making Practical Decisions in Librarianship Mini-Workshop,...

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

jeldredge@salud.unm.eduCopyright © 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