Research MethodsObjectives

– Understanding sampling– Understanding different research designs– Understanding strengths and weaknesses of

different designs– Understanding difficulties of subluxation

research

*PURPOSE OF Experimental RESEARCH DESIGN

* To help the researcher answer the research question.

* “To control for possible rival hypotheses or extraneous variables that might compete with the independent variable as an explanation for the cause-effect relationship.”

*Subjects/Sampling

*Sampling process includes two steps*Choosing the subjects to be included

in the study*Determining which subjects receive

treatment

*Sample

* Must define the POPULATION. The more a definition is limited, the less applicability to the general population.

* A SAMPLE is a portion of the population investigated to draw conclusions about the entire population* Sampling is used because it is not practical to

use the entire population

*Sampling Bias

* Occurs when one of the two (or three) study groups differ in one or more variables that would affect the outcome of the study.

* Choosing a sample that is not reflective of the target population of the treatment

“Reporting of age data in clinical trials of arthritis. Deficiencies and solutions”

Arch Intern Med 1993:153:243-8

• Review of 73 studies• 9664 patients• 2.1% of sample of was over age of 65• 62% of NSAID are consumed by population over

65.• Older people more likely to have adverse reactions• In order to keep side effects minimal, older people

excluded.

*Types of Samples

* Convenience

* Random * Definition: each member of the population has

an equal opportunity to be included in the study

*Types of Random Samples

* Simple random sampling

* Stratified random sampling

* Cluster sampling

*Simple random sampling

* Purest form of sampling, but not necessarily the best. After defining the population each individual is randomly assigned a group.

*Stratified random sampling

* Used when certain characteristics of a population exhibit established proportions.

*Cluster sampling

* Gives everyone within a population an equal chance of being chosen for the study

* But subject to sampling error at each stage of clustering

*Random Sampling Methods

* Table of random numbers

* Computer generated numbers

* Draw straws, marbles, etc.

Sample size

The larger the sample the easier it is to measure small but significant effects

If the effects of the study are to be great, a smaller sample size could be used

If using parametric tests you need at least 30 subjects in each subgroup

Classifications of Research Design

• Pre-experimental

• Quasi-experimental

• Experimental

Pre-experimental (Descriptive)

• Purpose is to observe and describe

• Does not offer explanations, provide causes or provide evidence

• May lead to additional research

Types of pre-experimental design

• Surveys

• Case reports

• Case series

• Historical research

Case Reports

• Not experimental and can not prove anything, but still very important

• AIDS, Lyme disease first described as a case reports

• X----------------O X is the independent variable (treatment) and O is the observation of the dependent variable (blood pressure, weight, pain)

Case Series

• Also known as “one group pretest-posttest design”

• Same as case report but uses a group

• O--------------X-------------O

Pre-experimental design

• Strengths– Inexpensive

– Relatively easy to perform

• Weaknesses– Minimal controls

– Cannot show contributory cause

Quasi-Experimental Designs

• Characterized by moderate controls

• Non-equivalent control group design

• O----------X-----------O O-----------------------O

Quasi-experimental design

• Strengths– Relatively easy to

perform

– Less expensive than experimental design

• Weakness– Moderate controls

– Cannot show contributory cause

True experimental design

• Use of strong controls• Random assignment to

groups• Manipulation of the

independent variable

• R-----O-----X-----O R-----O------------O

Experimental design

• Strengths– Strong controls

– Can show contributory cause

• Weaknesses– Expensive

– Difficult to perform

– Ethical issues relating to control group

– Participant recruitment often a problem

Other Forms of Research

• Meta Analysis (Putting together the data from various RCT’s)

• Qualitative studies (Objective study of the human experience using nonstatistical analysis)

Other common design terms

• Cross-sectional study– Measurement of presumed cause and effect at

the same time– Capable of measuring prevalence (proportion of

pop. with outcome at one point in time)• Doctor visit common prior to ones death. Is the

doctor visit a risk factor?

• Cross-over design: treatment group and control group switch roles

Other common design terms

• Longitudinal Study: carried out over time• Retrospective: Grouping by presence or absence

of outcome and review of past history– Hypertension study grouped by outcome, presence or

absence of hypertension

• Prospective : Observations made over a period of time as the events occur– A RCT is a longitudinal prospective study

The Case Report

Objectives

• Understand the importance of the case report in biomedical literature

• Know different designs of case reports

• Understand the structure of the case report and the elements of each section

Hierarchy of Knowledge• Randomized Clinical Trial

• Clinical trials

• Case Series

• Case Studies

• Antedotal Reports

• Testimonials

• Observations

• Rumors/Assertions.

• In 1985 the Journal of the American Medical Association republished 51 landmark articles to mark it’s first century of publication. 5 of the 51 were case reports.

• 20% to 30% of research articles involve less than 10 subjects.

A case report is….

• “biomedical story-telling”

• delivery vehicle for clinical education

• stimulant for more comprehensive and prospective research.

A case report is not….

• Antedotal

• A Testimonial

• A testimonial without sensationalism

• An advertisement….. Although it sometime is.

Types of Case Reports

• Descriptive: Purely descriptive of a condition or situation

• Interventive: Involves intervention on the part of the treating doctor.

Case Report Design

• One shot case study– Intervention then outcome assessment

• Pre-test, post-test design– Initial measurement, intervention, outcome

measurement

• Time-series (A-B-A)– Repeated measurements on and off treatment.

Case Series

• Variation on solitary case report

• Multiple individuals with same diagnosis and treatment being studied

• Each case may be separately described or lumped together with data summaries.

Structure

• Abstract

• Introduction

• Case Report

• Discussion

• Conclusion

• References.