Quantitative Research
Richard Peacock, Clinical Librarian
Archway Healthcare Library
Ziba Nadimi, Outreach and Information Skills LibrarianCamden Primary Care Trust
Definition
A study that aims to quantify attitudes orbehaviours, measure variables on which theyhinge, compare, and point out correlations. Itis most often conducted via a survey on asampling that must be representative so thatthe results can be extrapolated to the entirepopulation studied. It requires thedevelopment of standardised and codifiablemeasurement instruments (structuredquestionnaires).
Ipsos- A Market Research Co.
Quantitative Data Collection
•Requires a specific protocol
•Protocol is specified in advance of datacollection
•Population and sample should be large.The larger the better
Data Analysis
•Statistical analysis
•Describes trends, compares groups,relates variables
•Compares your results with past research
The Anatomy of a Research Paper
•Introduction
•Methods
•Results
•Discussion
The Anatomy of a Research Paper cont.
•The introduction summarises thebackground to the study
•The methods helps to understand if you arecritically appraising a paper
•The results reports findings objectivelywithout speculation or interpretation
•In the discussion the authors interpret thefindings in light of the study design and otherresearch
Levels of Evidence
Systematic Review
•Identifies an intervention for a specific disease orother problem in health care
•Determines whether or not this interventions works
•Authors locate, appraise and synthesise evidencefrom as many relevant scientific studies as possible
•They summarise conclusions about effectiveness
•They provide a collation of the known evidence on agiven topic
•Statistical methods (meta-analysis) may or may notbe used to analyse and summarise the results
Advantages of Systematic Reviews
•Adhere to a strict design, therefore minimisethe chance of bias
•Provide a scientific rather than subjectivesummarisation of literature
•Large amounts of information can beassimilated quickly by healthcare providers,researchers, and policymakers
•Compare results of different studies toestablish generalisability of findings andconsistency of results
Disadvantages of Systematic Reviews
•Experts may select only supportive evidence
•Papers with more interesting result morelikely to be published
•SRs may be biased due to exclusion ofrelevant studies and inclusion of inadequatestudies
•SRs include an element of judgement,whatever method is used e.g. authors of tobaccoindustry affiliated reviews are more likely to concludethat passive smoking is not harmful
Randomised Controlled Trials- RCTs
•Two or more interventions are compared bybeing randomly allocated to participants
•Includes a control intervention or nointervention
•If possible should be single/ double/ tripleblinded
Blinding in RCTs
•Preventing those involved in a trial fromknowing to which comparison group, i.e.experimental and control, a particularparticipant belongs
•The risk of bias is minimised
•Participants, caregivers, outcome assessorsand analysts can all be blinded
•Blinding of certain groups is not alwayspossible, e.g. surgeons in surgical trials
•Single, double and triple blind are in commonuse
Cohort Studies
•An observational study
•A defined group of people (the cohort) isfollowed over time
•Outcomes are compared to examine peoplewho were exposed or not exposed to aparticular intervention
•A retrospective cohort study identifies subjectsfrom past records and follows them to the present
•A prospective cohort study assemblesparticipants and follows them into the future
Case Control Studies
•Compares people with a specific disease oroutcome of interest (cases) to people fromthe same population without that disease oroutcome (control)
•Seeks associations between the outcomeand prior exposure to particular risk factorse.g. one group may have been exposed to aparticular substance that the other was not
•They are usually retrospective
Case Series
•A study reporting observations on a series ofindividuals, usually all receiving the sameintervention, with no control group.
Odds-Ratio Diagram (Blobbogram)
Odds-Ratio Diagram Cont.
•Included in CDSR and other good systematicreviews
•Presents complicated results and concepts ina clear visual format
•For each individual trial, the odds-ratio resultis represented by a box
•The vertical line is an odds-ratio of oneknown as “line of no effect”
•The horizontal line is the “confidence interval”for that result
Odds-Ratio Diagram Cont.
•Confidence Interval - the range in which weare 95% or 99% confident that the ‘real’ resultof the study lies when is extrapolated to thewhole of the population sampled in the study
•The diamond is called meta analysis – thestatistical method of combining the results ofdifferent RCTs for the same intervention
Odds-Ratio Diagram Cont.
•Results to the left of the line of no effect =less of the outcome in the experimentalgroup
•Results to the right of the line of no effect =more of the outcome in the experimentalgroup
•It is important to note whether the outcome isgood or bad
Odds-Ratio Diagram Cont.
•If CI crosses line of no effect = inconclusiveresults
•Longer CI = smaller study (less confident ofresults)
•Shorter CI = bigger study (more confident ofresults)
P Values
•P for probability (ranging from zero to one)
•The result could have occurred by chance ifin reality the null hypothesis was true
•The null hypothesis- the factor of interest (e.g.treatment) has no impact on outcome (e.g.risk of death)
•P value of less than 0.05 means likelihood ofresults being due to chance is less than 1 in20 = “Statistically significant”
References
McGovern, D.P.B. etal, Evidence-based medicine, BIOS ScientificPublishers Ltd., 2001
Greenhalgh, T., How to read a paper, 3rd ed., BMJ Publishing Group,2006
Kelsey, K.D., (Lecture 2) Quantitative and qualitative approaches toresearch- PowerPoint Presentation
Ward, L., Critical reading made easy:effectiveness and experience,University Hospitals of Leicester NHS Trust- PowerPoint Presentation
Jackson, N., Conducting systematic reviews of public health andhealth promotion interventions, Cochrane Health Promotion and PublicHealth Field- PowerPoint Presentation
The Cochrane Library’s Glossary of Terms, Wiley InterScience
Andrew Hayward, Critical Appraisal of Analytical Studies- PowerPointPresentation