Sampling and Data Collection

1
Sampling and Data Collection

• Research Methodologies
• in Allied Health
• Peg Bottjen, MPA, MT(ASCP)SC

2
(No Transcript)
3
Research Process
Planning
Hypothesis or Aims
Research Design
Data collection
Organization and Presentation of Data
Data Analysis
Interpretation and Conclusions
4
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.

5
Boundaries of the Study

• Define the terms
• Dictionary definitions
• ex. BMI wt (kg) / ht2 (m)
• Reference to a definition
• ex. NHANES II study
• Operational definitions
• ex. obesity gt95th percentile

6
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.

7
More Boundaries of the Study

• Assumptions
• Scope
• Limitations
• Subjects

8
Sampling
Target Population
Representative Sample
X
X
X
X
X
9
Representative Sampling Methods

• Randomized roll of dice
• Area - location
• Systematic choose from list (every 5th)
• Volunteer ask for participants
• Convenience what is available

10
Subjects

• Inclusion
• Exclusion

11
Sample Size

• It depends!
• Procedures used to collect data
• Statistical level of significance
• Statistical power
• Effect size

12
External Validity

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

Polgar Thomas-4th Ed. 2001
13
Internal Validity

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

14
Data Collection Methods

• Questionnaire
• Interview
• Observation
• Measurement / instrumentation

15
Questionnaire

• Define information needed
• Draft questions
• Do pilot
• Redraft
• Administer questionnaire

16
Questionnaire

• Open vs Closed questions
• Scaled questions or statements
• Likert scale
• Strongly disagree, disagree, no opinion, agree,
  strongly agree
• Semantic differential
• Draw an x at point that best describes your
  feeling
• Powerless
  Powerful

X
17
Interview

• Structured
• Unstructured

18
Observation

• Who is observer
• Setting of observation
• Use of instrumentation

19
Observation

• Complete participant
• Participant as observer
• Observer as participant
• Complete observer

20
Measurement / Instrumentation

• Subjective measurements
• Ratings or judgments by humans of quantities or
  qualities
• Objective measurements
• Measurement of physical quantities or qualities
  by equipment

21
Measurement / Instrumentation

• Objective measurement
• Data 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 tests
• Eg. SAT, ACT, GRE, CAT, Myers-Briggs, IQ test,
  patient quality of life (SF-36)

22
Desirable Properties of Measurement Tools

• Reliability
• Validity
• Applicability
• Practicality

23
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

24
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 -
25
Validity of Mammography
Mammography Result Known Breast Cancer
169 ( true )
- 49 (false -)
26
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?

27
(No Transcript)
28
Summary

• Boundaries of the study
• Sampling
• Data Collection Methods
• Reliability/ Validity

29
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?

30
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.