Study designs in oncology

Study Designs in Oncology
Doing it right first time
Dr.Ram Madhavan M.D
Radiation Oncology Division
Amrita Institute of Medical Sciences, Kochi

Study design is a systematic way of dealing with these
issues, and offers a good-practice blueprint.
• What is the research question? What are we hypothesizing?
• Which is our main outcome variable ?
• How many subjects need to be included in the study?
• Who exactly are the subjects? How should we select them?
• Are we going to make some form of clinical intervention or simply observe? And
so on
2Young Radiation Oncologist's Forum

Most problems in studies are due to
poor design (not poor analysis)
• Errors in design cannot be corrected after the study has been
completed
• About two thirds of 56 typical errors in studies are connected to
errors in design and performance
Sackett DL:Bias in analytic research.J Chronic Dis 1979; 32: 51–63.

Six aspects of study designs
• Question to be answered
• Study population
• Type of study
• Unit of analysis
• Measuring technique
• Calculation of sample size

1. The Research Question
• When I came to practice I was looking for answers like everybody else.
For years I asked "what's the right answer?" Now I am learning "What
is the right question?"

What is the quality of life ? X
• What is the quality of life of pre
menopausal women diagnosed with
stage III breast cancer after Breast
conservation treatment compared to
women who had undergone
mastectomy in India assessed using
EORTC QLQ C30 questionnaire ?

2. Study population
• We usually study a sample of individuals who are assumed to be
representative of a wider group.

How do we ensure that the sample is as
representative as possible?
• Most representative sample is a simple random sample.
• Every member of the population must have an equal chance of being
included in the sample.
• Require a complete and up-to-date list [sampling frame]
• Example, every newly diagnosed breast cancer patient in the Kerala in
2016.

Systematic random sampling
• Some fixed fraction of the sampling frame is selected, say every 10th
or
every 50th
member, until a sample of the required size is obtained.
Stratified sampling
• Sampling frame is first broken down into strata like nonsmokers, ex-
smokers and smokers.
• Then each separate stratum is sampled using a systematic sampling
• Finally these strata samples are combined

Contact or consecutive samples
• Individuals in current or recent contact with the clinical services, such
as consecutive attendees at a clinic.
• For example, last 500 breast cancer patients attending the two RCCs
at Kerala.
• In a multicenter study the required number of patients can be
reached within a shorter period and the results can more readily be
generalized.

3. Types of studies
• An observational study is one in which researchers actively observe
the subjects involved, but they don’t control, change or effect in any
way, their selection, treatment or care.
• An experimental study does involve some sort of active intervention
with the subjects.

Observational studies
•Case-series.
•Cross-section studies.
•Cohort studies.
•Case-control studies

Case series studies
• A health carer may see a series of patients with similar but unusual
symptoms or outcomes, ﬁnd something interesting and write it up as
a study.
• Case-series studies often point to a need for further investigations.

An example from practice
• In 1981 a drug technician at the Centre for Disease Control in the
USA, noticed an unusually high number of requests for the drug
pentamidine, used to treat Pneumocystis carinii pneumonia
• This led to a case-series study, of PCP occurring unusually in five gay
men in Los Angeles.
• At the same time a similar outbreak of Kaposi’s Sarcoma (previously
rare) in a small number of young gay men in New York.
• These events signaled the arrival of HIV in the USA.

Cross sectional studies
• A cross-section study aims to take a ‘snapshot’ of some situation at
some particular point in time, but notably data on one or more
variables from each subject in the study is collected only once.

• A cross-sectional study was conducted in a nationally representative
sample of 27,035 United States (U.S.) adults to estimate the
prevalence of chronic pain and to describe socio demographic and
other characteristics of chronic pain

From here to eternity – cohort studies
• The main objective of a cohort study is to identify risk factors causing
a particular outcome, for example lung cancer.
• Cohort study is also known as follow-up, prospective, or longitudinal
study.

• Prospective cohort study was that conducted by Doll and Hill into a
possible connection between mortality and cigarette smoking.
• Recruited about 60 % of the doctors in the UK, determined their age
and smoking status and then followed them up over the ensuing
years, recording deaths as they arose.
• Very quickly the data began to show signiﬁcantly higher mortality
among doctors who smoked.

Back to the future – case-control studies
• In Case-control study the groups are selected on the basis of having or not having
the outcome or condition.
• The case control study is also known as retrospective longitudinal study.

• A case–control study was conducted in Singapore to investigate the
role of diet in breast cancer.
• Two hundred Chinese women with histologically confirmed breast
cancer and 420 controls without this disease participated in the
study.
• A dietary questionnaire was used to measure past dietary intake.
• Cases and controls were then compared to assess whether there
were any differences in their past intake of selected foods and
nutrient

Getting stuck in – experimental studies
• The investigators actively participate in some aspect of the
recruitment, treatment or care of the subjects in the study.

Randomization
• Make the groups similar.
• Take the allocation process out of the hands of the researcher.
• If the randomization is successful, and the original sample is large
enough, then the two groups should be more or less identical,
differing only by chance. This design is thus called the randomized
controlled trial (RCT).

4. Unit of analysis
• In a typical clinical study, the patient is the unit of analysis.
• It may also be a technical model, hereditary information, a cell, a
cellular structure, an organ, an organ system, a single test individual
(animal or man), or specified subgroup or the population
• In systematic reviews, the unit of analysis is a single study

5. Measuring technique
• Measuring instruments which specifically record measuring data
(such as blood pressure or laboratory parameters)
• Data collection with standardized or self-designed questionnaires (for
example, quality of life, depression, or satisfaction).
• Measurement plan
• Type of scale used.

Summary of important terms to validate a
measurement method

6. Sample size
• Exploiting knowledge of the expected effect (for example, the clinically relevant
difference) and its scatter (for example, standard deviation).
• These may be determined in preliminary studies or from published information.
• A large sample is required to discover a small difference.
• If the sample is small, the power will also be low, bringing the risk that real
differences will not be identified

Check List on Study Designs
Item Content
Research Question Is the question clearly defined ?
Study population Recruitment [Type, area, time]
Socio demographic information
Inclusion and exclusion criteria
Period of follow up
Type of study Research on secondary data
Research on primary data
__ observational
__ experimental

Check List on Study Designs
No. Item Content
3. Unit of Observation Technical model
Cell
Organ
Single test subject
Selected patient group
4 Measuring technique Reliability
Validity
Measurement plan
5. Calculation of sample size Power
Type of test
Level of significance

Thank you

Study designs in oncology

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