Planning The Measements: Precision And Accuracy

Question 1

Measurements

Answer 1

Describe phenomenon that can be analyzed statistically

Question 2

Precise

Answer 2

Free of random error

Question 3

Accurate

Answer 3

Free of systematic error

Question 4

Continuous variables

Answer 4

Are quantified on an infinite scale

Question 5

Discrete variable

Answer 5

Units who are limited to integers. Can resemble continuous variables if large enough values are used

Question 6

Categorical variable

Answer 6

Not suitable to be quantified

Question 7

Dichotomous variable

Answer 7

Categorical variable with two possible values

Question 8

Ordinal categorical variable

Answer 8

Categories that have an order (e.g. Severe, moderate, mild pain)

Question 9

Random error

Answer 9

The greater the error, the less precise the measurement

Question 10

Three main sources of random error

Answer 10

• Observer variability refers to variability in measurement that is due to the observer, and includes such things as choice of words in an interview and skill in using a mechanical instrument
• Instrument variability refers to variability in the measurement due to environmental factors such as temperature, aging mechanical components, different reagent lots, and so on
• Subject variability refers to intrinsic biologic variability in the study subjects due to such things as fluctuations in mood and time since last medication

Question 11

Within-subject standard deviation

Answer 11

Reproducibility of continuous variables depends on this standard deviation

Question 12

What should be used if the standard deviation and the participant’s mean demonstrates a linear association?

Answer 12

The coefficient of variation

Question 13

How does one assess precision in categorical variables?

Answer 13

Using percent agreement and the kappa statistic

Question 14

What are the 5 strategies for enhancing precision?

Answer 14

1. Standardizing the measurements
2. Training certifying the observers
3. Refining the instruments
4. Automating the instruments
5. Repetition

Question 15

Accuracy

Answer 15

Is the degree to which it actually represents what it is intended to represent

Question 17

What are the three main classes of measurement error?

Answer 17

• Observer bias is a distortion, conscious or unconscious, in the perception or reporting of the measurement by the observer.it may represent systematic errors in the way an instrument is operated, such as a tendency to round down blood pressure measurements, or in the way an interview is carried out as in the use of leading questions
• Instrument bias can result from faulty function of a mechanical instrument
• Subject bias is a distortion of the measurement by the study subject, for example, in reporting an event (respondent or recall bias).

Question 18

Gold standard

Answer 18

Accuracy of a measurement can be best assessed by comparing it with a “gold standard”—a reference technique that is considered accurate

Question 19

What are the three ways to view and assess validity?

Answer 19

• Content validity examines how well the assessment represents all aspects of the phenomena under study—for example, including questions on social, physical, emotional, and intellectual functioning to assess quality of life.
• Construct validity refers to how well a measurement conforms to theoretical constructs; for example, if an attribute is theoretically believed to differ between two groups a measure of this attribute that has construct validity would show this difference
• Criterion-related validity is the degree to which a new measurement correlates with well-accepted existing measures.

Question 20

Face validity

Answer 20

Uses subjective judgments

Question 21

Predictive validity

Answer 21

The ability of the measurement to predict an outcome: the validity of a measure of depression would be strengthened if it was found to predict suicide

Question 22

What is a general approach to validating an abstract measure?

Answer 22

Search the literature and consult with experts to find a suitable instrument

Question 23

Measurement sensitive

Answer 23

Measurements should be able to detect differences in a characteristic that are important to the investigator

Question 24

Measurement specificity

Answer 24

A measurement should be specific so therefore should only represent the characteristic of interest (e.g. The carbon monoxide level in expired air is a measure of smoking habits that is only moderately specific because it can also be affected by other exposures such as automobile exhaust

Question 25

Measurement appropriateness

Answer 25

Measurements should be appropriate to the objectives of the study. A study of stress as an antecedent to myocardial infarction would need to consider which kind of stress (psychological or physical, acute or chronic)

Question 26

Distribution of responses

Answer 26

Measurements should provide adequate distribution of responses in the study population. Values should be dispersed

Question 27

Efficiency and parsimony of a study is described as what?

Answer 27

As collecting data with measurements that are at an affordable cost in time and money

Question 28

Operational manual

Answer 28

Describes the method for conducting and recording the results of all measurements made in the study. To standardize instructions from examiner to examiner and from subject to subject, the protocol includes a script of instructions to be read to the participants verbatim

Question 35

Precision (reproducibility, reliability, and consistency)

Answer 35

Is the degree to which it is reproducible, with nearly the same value each time it is measured

Question 36

What are the 7 strategies of enhancing accuracy

Answer 36

1. Standardizing the measurement methods
2. Training and certifying the observers
3. Refining the instruments
4. Automating the instruments
5. Making unobtrusive measurements
6. Calibrating the instrument
7. Blinding