Quantitative Research

Richard Peacock, Clinical Librarian

Archway Healthcare Library

Ziba Nadimi, Outreach and Information Skills Librarian Camden Primary Care Trust

                                                                   

                         

Definition

A study that aims to quantify attitudes or behaviours, measure variables on which they hinge, compare, and point out correlations. It is most often conducted via a survey on a sampling that must be representative so that the results can be extrapolated to the entire population studied. It requires the development of standardised and codifiable measurement instruments (structured questionnaires).

Ipsos- A Market Research Co.

Quantitative Data Collection

• Requires a specific protocol • Protocol is specified in advance of data

collection• 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 the background to the study

• The methods helps to understand if you are critically appraising a paper

• The results reports findings objectively without speculation or interpretation

• In the discussion the authors interpret the findings in light of the study design and other research

Levels of Evidence

Primary Research

Experimental

observational

SecondaryResearch

For qualitative studies? No consensus about the relative rigour of different methods

Systematic reviews &

Meta-analyses

Randomised controlled trials

Cohort studies

Case control studies

Case series

For quantitative studies

Systematic Review

• Identifies an intervention for a specific disease or other problem in health care

• Determines whether or not this interventions works• Authors locate, appraise and synthesise evidence

from as many relevant scientific studies as possible• They summarise conclusions about effectiveness• They provide a collation of the known evidence on a

given topic• Statistical methods (meta-analysis) may or may not

be used to analyse and summarise the results

Advantages of Systematic Reviews• Adhere to a strict design, therefore minimise

the chance of bias• Provide a scientific rather than subjective

summarisation of literature• Large amounts of information can be

assimilated quickly by healthcare providers, researchers, and policymakers

• Compare results of different studies to establish generalisability of findings and consistency of results

Disadvantages of Systematic Reviews• Experts may select only supportive evidence• Papers with more interesting result more

likely to be published• SRs may be biased due to exclusion of

relevant studies and inclusion of inadequate studies

• SRs include an element of judgement, whatever method is used e.g. authors of tobacco industry affiliated reviews are more likely to conclude that passive smoking is not harmful

Randomised Controlled Trials- RCTs

• Two or more interventions are compared by being randomly allocated to participants

• Includes a control intervention or no intervention

• If possible should be single/ double/ triple blinded

Blinding in RCTs

• Preventing those involved in a trial from knowing to which comparison group, i.e. experimental and control, a particular participant belongs

• The risk of bias is minimised• Participants, caregivers, outcome assessors

and analysts can all be blinded• Blinding of certain groups is not always

possible, e.g. surgeons in surgical trials• Single, double and triple blind are in common

use

Cohort Studies

• An observational study• A defined group of people (the cohort) is

followed over time• Outcomes are compared to examine people

who were exposed or not exposed to a particular intervention

• A retrospective cohort study identifies subjects from past records and follows them to the present

• A prospective cohort study assembles participants and follows them into the future

Case Control Studies

• Compares people with a specific disease or outcome of interest (cases) to people from the same population without that disease or outcome (control)

• Seeks associations between the outcome and prior exposure to particular risk factors e.g. one group may have been exposed to a particular substance that the other was not

• They are usually retrospective

Case Series

• A study reporting observations on a series of individuals, usually all receiving the same intervention, with no control group.

Odds-Ratio Diagram (Blobbogram)

Odds-Ratio Diagram Cont.

• Included in CDSR and other good systematic reviews

• Presents complicated results and concepts in a clear visual format

• For each individual trial, the odds-ratio result is represented by a box

• The vertical line is an odds-ratio of one known 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 we are 95% or 99% confident that the ‘real’ result of the study lies when is extrapolated to the whole of the population sampled in the study

• The diamond is called meta analysis – the statistical method of combining the results of different 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 experimental group

• Results to the right of the line of no effect = more of the outcome in the experimental group

• It is important to note whether the outcome is good or bad

Odds-Ratio Diagram Cont.

• If CI crosses line of no effect = inconclusive results

• Longer CI = smaller study (less confident of results)

• Shorter CI = bigger study (more confident of results)

P Values

• P for probability (ranging from zero to one)• The result could have occurred by chance if

in 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 of results being due to chance is less than 1 in 20 = “Statistically significant”

ReferencesMcGovern, D.P.B. etal, Evidence-based medicine, BIOS Scientific Publishers Ltd., 2001

Greenhalgh, T., How to read a paper, 3rd ed., BMJ Publishing Group, 2006

Kelsey, K.D., (Lecture 2) Quantitative and qualitative approaches to research- 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 and health promotion interventions, Cochrane Health Promotion and Public Health Field- PowerPoint Presentation

The Cochrane Library’s Glossary of Terms, Wiley InterScience

Andrew Hayward, Critical Appraisal of Analytical Studies- PowerPoint Presentation