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Chapter 10

Clarifying Measurement and Data Collection in Quantitative Research

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Concepts of Measurement Theory

Directness of measurement Measurement error Level of measurement Reliability Validity

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Directness of Measurement

Directness of measurement Direct measures (concrete things such as oxygen

saturation, temperature, weight) Indirect measures (abstract concepts such as

pain, depression, coping, self-care, and self-esteem)

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Measurement Error

Difference between the true measure and what is actually measured Systematic error: the variation in measurement is

in the same direction Random error: the difference is without pattern

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Levels of Measurement

Nominal Ordinal Interval Ratio

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Nominal-Scale Measurement

Lowest of the four levels of measurement Categories that are not more or less, but are

different from one another in some way Mutually exclusive and exhaustive categories Named categories

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Example of Nominal Data

Gender 1 = Male 2 = Female

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Ordinal-Scale Measurement

Order/ranking imposed on categories Numbers must preserve order

1 = Tallest 2 = Next tallest 3 = Third tallest

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Interval-Scale Measurement

Numerical distances between intervals Absence of a zero point Likert scale scores

1 = Strongly disagree 2 = Disagree 3 = Neutral 4 = Agree 5 = Strongly agree

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Ratio-Scale Measurement

Highest for measurement Continuum of values Absolute zero point

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Example of Ratio Data

Test scores 1 = Lowest third percentile 2 = Middle third percentile 3 = Top third percentile

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Reference of Measurement

Norm-referenced testing Tests performance standards that have been

carefully developed over years with large, representative samples using a standardized test with extensive reliability and validity

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Reference of Measurement (cont’d)

Criterion-referenced testing Comparison of a subject’s score with a criterion of

achievement that includes the definition of target behaviors

• When behaviors are mastered, the subject is considered proficient in the behaviors.

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Reliability Testing

Concerned with how consistently the measurement technique measures the concept of interest

Needs dependability, consistency, accuracy and comparability

If expressed as a correlation coefficient, 1.00 is perfect reliability, whereas 0.00 is no reliability.

The lowest acceptable coefficient for a well-developed measurement tool is 0.80.

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Types of Reliability

Stability: Concerned with the consistency of repeated measures or test-retest reliability

Equivalence: Focused on comparing two versions of the same instrument (alternate forms reliability) or two observers (interrater reliability) measuring the same event

Homogeneity: Addresses the correlation of various items within the instrument or internal consistency; determined by split-half reliability or Cronbach’s alpha coefficient

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Interrater Reliability

Consistency in raters % = number of behaviors performed/total number

of behaviors

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Critiquing for Reliability

1. What reliability information is provided?2. Does the author include reports of the

validity of the instrument from previous studies?

3. Did the author perform pilot studies to examine the validity of the instrument?

4. Did the researcher report use of data from the present study to examine instrument validity in the discussion section of the report?

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What Is Validity?

It is the extent to which an instrument reflects the concept being examined.

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Physiological Measures

Accuracy Selectivity Precision Sensitivity Sources of error

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Critiquing Methods of Measurement

Were the measurement strategies clearly identified and described?

What level of measurement was achieved by each instrument?

Was the reliability of each measurement method adequate?

Was the validity of each measurement method adequate?

If physiological instruments were used, were they accurate and precise?

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Measurement Strategies in Nursing

Physiological measurements Observational measurements Interviews

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Examples of Physiological Measures

Physical measurement methods ECG, BP, I&O SVO2, pulse oximetry

Microbiological Smears Cultures, number of CFU Sensitivities

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Observational Measurements

Unstructured observations Structured observations

Category systems Checklists Rating scales

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Critiquing Observational Measurement

1. Is the object of observation clearly identified and defined?

2. Is interrater reliability described?3. Are the techniques for recording

observations described?

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Types of Interviews: Unstructured

Uses broad questions Describe for me your experience with… Role of interviewer is to encourage continued

discussion

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Examples of Unstructured or Open-Ended Interview Questions

Tell me about... What has been your experience with... What was it like to hear you have cancer?

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Types of Interviews: Structured

Structured interviews Describing interview questions Pretesting the interview protocol Training interviewers Preparing for an interview Probing Recording interview data

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Closed-Ended Interview Questions

Structured Response alternatives fixed Which would you rather do, x or y?

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Critiquing Interview Methods

1. Do the interview questions address concerns expressed in the research problem?

2. Are the interview questions relevant for the research purpose and objectives, questions, or hypotheses?

3. Does the design of the questions tend to bias subjects’ responses?

4. Does the sequence of questions tend to bias subjects’ responses?

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Focus Groups

Used to study qualitative issues Obtain participants’ perceptions of narrow

subject in a group interview session Give group a feeling of “safety in numbers” Nonverbal approaches are included. Discussion helps to provide depth of data.

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Focus Group Considerations

May sort participants into smaller groups with common characteristics: segmentation

Need to select an effective moderator to keep discussion on track

The setting should be relaxed and comfortable.

High-quality tape recordings should be made.

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Critiquing the Use of Focus Groups

1. What was the aim of the focus group?2. Was the group size appropriate for the focus

group method?3. Was group sufficiently homogeneous to

speak candidly?4. Was moderator successful in keeping

discussion focused?

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Critiquing the Use of Focus Groups (cont’d)

5. Was the aim of the focus group achieved?6. Did conclusions appear to be

representative?7. Were minority positions identified and

explored?

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Measurement Strategies

Questionnaires Scales Q methodology Diaries Delphi technique

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Questionnaires

Administration In person/on phone Self-administered Mail

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Scales

Rating scales The Likert scale Semantic differential scales Visual analog scales

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Example of Items in a Likert Scale

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Example of Visual Analog Scale

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Critiquing a Scale

1. Is the instrument clearly described?2. Are the techniques that were used to

administer and score the scale provided?3. Is information about validity and reliability of

the scale described from previous studies?4. Is information about validity and reliability of

the scale described for the present sample?5. If the scale was developed for the study, was

the instrument development process described?

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Critiquing the Data Collection Process

Was data collection process clearly described?

Was data collection conducted in a consistent way?

Were research controls maintained? If data collectors were used, were they

adequately trained?

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Serendipity

The accidental discovery of something useful or valuable.

Can lead to new insights