Sampling and Data Collection

Research Methodologies

in Allied Health

Peg Bottjen, MPA, MT(ASCP)SC

Research Process

Planning

Hypothesis or Aims

Research Design

Data collection

Organization and Presentation of Data

Data Analysis

Interpretation and Conclusions

Objectives

Upon completion of this unit the student will be able to:

• Outline advantages and disadvantages of three sampling methods • Operationally define the variables in a study • Identify limitations in research studies • Choose the method of data collection that best facilitates proving or disproving a hypotheses or best answers a research question • Explain how a test can be valid yet not reliable.

Boundaries of the Study

Define the terms

Dictionary definitionsex. BMI – wt (kg) / ht2 (m)

Reference to a definitionex. NHANES II study

Operational definitionsex. obesity >95th

percentile

Operational Definition

The operational definition of a variable is a statement of how the researcher in a particular study chooses to measure the variable in question.

More Boundaries of the Study

Assumptions

Scope

Limitations

Subjects

Target Population

Representative Sample

Sampling

XX

X

X

X

Representative Sampling Methods

Randomized – roll of diceArea - locationSystematic – choose from list (every 5th)Volunteer – ask for participantsConvenience – what is available

Subjects

Inclusion

Exclusion

Sample Size

It depends! Procedures used to

collect data Statistical level of

significance Statistical power Effect size

External Validity

The extent to which the results of an investigation can be generalized to other samples or situations.

Polgar & Thomas-4th Ed. 2001

Internal Validity

The intervention was responsible for the differences or lack of differences observed.

Data Collection Methods

QuestionnaireInterviewObservationMeasurement / instrumentation

Questionnaire

Define information neededDraft questionsDo pilotRedraftAdminister questionnaire

Questionnaire

Open vs Closed questionsScaled questions or statements

Likert scaleStrongly disagree, disagree, no opinion, agree,

strongly agreeSemantic differential

Draw an x at point that best describes your feeling

Powerless Powerful

X

Interview

Structured

Unstructured

Observation

Who is observer

Setting of observation

Use of instrumentation

Observation

Complete participant

Participant as observer

Observer as participant

Complete observer

Measurement / Instrumentation

Subjective measurementsRatings or judgments by humans of

quantities or qualities

Objective measurementsMeasurement of physical quantities or

qualities by equipment

Measurement / Instrumentation

Objective measurementData collected by instrumentation

Eg. Blood glucose, MR/CT scans, radiographic image, nuclear medicine scan, activated clotting time (ACT), nutrition screening instrument, stained slide read by expert

Data collected by standardized testsEg. SAT, ACT, GRE, CAT, Myers-Briggs, IQ

test, patient quality of life (SF-36)

Desirable Properties of Measurement Tools

ReliabilityValidityApplicabilityPracticality

Reliability - Precision

The test or assessment measures the same thing every time and results in the same answer every time.

Test-retest – correlates 1st to 2nd Inter-observer – between different observers Internal consistency – between items

measured

Validity - Accuracy

The test or assessment measures what it claims to measure. Sensitivity - % true positive Specificity - % true negative

Test Result Disease Present Disease Absent

+ True + False +

- False - True -

Validity of Mammography

Mammography Result Known Breast Cancer

+ 169 ( true +)

- 49 (false -)

Validity

Predictive value Ability of a measurement to predict the

value of it or another test in the future (prognosis)

What is predictive value of an ACT score to your grade point average in college?

Summary

Boundaries of the studySamplingData Collection MethodsReliability/ Validity

Critical Evaluation of Research

Who comprised the sample? What was the inclusion criteria? What was the exclusion criteria? Was the sample biased? How is the independent variable defined? How is the dependent variable defined? How were validity issues addressed? How were reliability issues addressed?

Group Work

Questions 9 – 16 in the Research Proposal Notebook are designed to lead you through the process of the literature review, defining the research question, and selecting a research design. Answer each question in your group. Submit your results as described under Assignments.