Study Design in Scientific Research

8/3/2019 Study Design in Scientific Research

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STUDY DESIGN IN

SCIENTIFIC RESEARCH



Design the study• Aspects of study design:

- Experimental Units

- Type of study and sampling

- What to measure?

- How to measure?

- How to analyze?



Design the study• Observational Descriptive study: Here

observations made of a single sample are

reported.

• Observational Analytical study: Hereobservations of similarities/differences in two or

more samples are reported

• Experimental/Interventional Study: Here the

outcome of an intervention in one group iscompared to another group where no intervention

is made.



Observational Descriptive Studies

• These are simplest types of studies and

include case reports and case series.

– Case Reports: These are best looked upon as a

means to generate hypotheses about disease

processes. They usually report an unusual event

in respect to a disease.

– Case Series: These report observations in a

group of patients. They are good for studying

rare disorders or reporting treatment outcomes

of interventions like surgery.



Observational Analytical Studies

• Here observations in two or more groups

are compared without researchers making

an intervention. Two main types are case-

control studies and cohort studies

– Case-Control Studies– Cohort Studies




• Case-Control Studies

Here the researcher is looking for the possible

causes of an identified outcome.

– A group of subjects with the outcome is

compared with a matched control groupwithout the outcome.

– The difference in exposures and risk factors

between the two groups is then analysed

retrospectively.





• Example:

TMD in orthodontic patients compared to

non orthodontic patients

• case-control studies are usuallyretrospective, but not always





– Pros: Cheap to run, few subjects required thus

quicker yield of results

– Cons: Difficult to recruit matching control

group, relies on recall and reporting of risk

factors, not good for rare exposures, difficult to

establish temporality of exposure and outcome.



Case Control StudiesTime

Direction of inquiry

Cases

(People with

the disease)

Population

Controls

(Similar peoplewithout

the disease)

Exposed

Not exposed

Exposed

Not exposed

Finish Start




• Cohort Studies

• Here the researcher is looking at whether an

exposure or risk factor results in an

outcome.

– A group of subjects with the exposure iscompared with a matched group without the

exposure.

– Both groups are then observed or ‘followed up’

to see the difference in development of theoutcome between the two groups.



Cohort StudiesTime


People

without

the disease

Start

Population

Exposed

Not

exposed

Disease

No disease

Disease

No disease

Finish




• Cohort Studies

– Pros: Good for rare exposures, assessment of

temporality, estimation of disease incidence.

– Cons: Expensive to set up, unsuitable for rare

outcomes, prolonged follow-up, selection bias,

drop outs, influenced by confounders, no

randomisation.



Experimental/Interventional Studies

• Here the researcher intervenes in a group of

subjects to assess the outcomes that the

intervention produces.

• There are several types of

experimental/interventional studies:– Open Trial

– Controlled Trial

– Randomised Controlled trial (RCT)

– Crossover Trial




• Open Trial

– Here all the test subjects receive the

intervention. There is no control group.

– This is a cheap and easy method of assessing

efficacy of an intervention.




• Controlled Trial

– Here there are two groups; one receives the

intervention and the other a placebo or sham

treatment.

– The outcomes in the two groups are then

compared.




• Randomised Controlled trial (RCT)

– Here in addition to there being a controlled

group, subjects are allocated to either group in a

random fashion.

– This prevents selection bias and equally

distributes possible confounders. If the process

is blinded this also prevents observation bias.

– RCTs are considered the gold standard way

to assess the efficacy of interventions.



Randomised Controlled Studies

• An investigation without bias.

• Bias is the systematic deviation of the results of a

study from the truth because of the way it has

been conducted, analysed or reported



Randomised Controlled Trials

• Controlled : Experimental & Control groups

• Randomised: Random selection of members of

experimental and control groups.

Randomisation Simple

Randomisation Randomised blocks

• Blinding Single-Blinded

Double-blinded



Randomised Controlled TrialsTime


Randomization

to groups

Sample

Population

Intervention

Control Measure outcome

Lost to follow-up

Non-participantsStart FinishMeasure outcome




• Randomised Controlled trial (RCT)

– Pros: Reliable measure of efficacy which can

be used in meta-analyses.

– Cons: Expensive to run, ethical issues around

not giving treatments to ill patients.




• Crossover Trial

– Here all subjects receive the same intervention.

Then half through the study the subjects cross

over to another treatment or placebo.

– This is useful when there are limited number of

subjects such in rare diseases.

– Not for conditions which can be cured with the

treatment or end up in death; only for chronic

diseases (pain, asthma, arthritis, psychological

problems).




• Crossover Trial

– Pros: Subjects behave as their own controls,

useful in rare diseases.

– Cons: Risk of carry-on effects of treatments

which require wash-out periods to eliminate the

effects.



Crossover Trials

Eligible/Consent

Randomize

Treatment

Treatment

Control

Control

Washout periodRun-in period



Systematic Reviews and Meta-analyses

• Systematic reviews are studies that

systematically search and analyse research

articles based on a clinical question.




• Reviews of particular importance are those

dealing with RCTs of a specific

intervention.

• Such reviews pool the results of several

studies to produce results that arestatistically more powerful, reliable and

accurate than the individual studies.




• Due to the value placed on systematic

reviews they are considered as a gold-

standard in evidence based medicine.

• The importance of systematic reviews has

led researchers to try and standardise onhow such studies should be reported in

published literature.




• The QUOROM statement (Quality of

Reporting of Metanalysis) was produced

during a conference of the same name in

1999.

• This has recently been superseded by thePRISMA statement (Transparent Reporting

of Systematic Reviews and Meta-analyses).

• The statement sets out checklist of 27 items

that authors should report in their review.




• Pros: Statistically powerful measures of

effect,

• Cons: Quality of meta-analysis limited by

the quality of original studies included or

available.



Study Designs : Summary

Study Design in Scientific Research

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