week 12 health measurement

Question 1

WHO definition of health

Answer 1

a state of complete physical, mental, and social well-
being, and not merely the absence of disease or
infirmity

• exposure to something resulting in a deviation of health can then be considered a disease

Question 2

how do we define health

Answer 2

commonly defined as a state free from illness or disease

Question 3

what is health-related quality of life

Answer 3

• many use the WHO definition
• an agreement that premature mortality is undesirable, so an aspect of health should be avoidance of death
• encompasses physical, mental, and social well-being, not just the absence of illness or disease
• involved more than just avoiding diseases
• maximizing HRQL becomes critical for enjoyment of long life

Question 4

psychometric approach

Answer 4

attempts to provide a separate measure for each dimension of HRQL

Question 5

decision theory

Answer 5

weighs the different dimensions to provide a single expression of health status
- argues each dimension of health is not equally of importance

*combination of both decision and psychometric approaches are used

Question 6

health measurement

Answer 6

All principles of health measurement apply the same, regardless of the topic!

Question 7

health surveys

Answer 7

estimation of health (prevalence, incidence, risks) are routinely done using health surveys

• fatal diseases are collected on health via hospital records
• health surveys can be specific (ex. depression) or can be broad (community health )

Question 8

what types of items are usually on health surveys

Answer 8

1. Dichotomous (Yes/No)
2. Likert-like (“In general, how do you rate your health?” –
   “Excellent / Very Good / Good / Fair / Poor”

Question 9

health assessment

Answer 9

dependent upon reliable and valid measures

in health, what is equally important, is the reliability and
validity in the classification of individuals

Question 10

what validity is most important for health measures

Answer 10

criterion validity

Question 11

medicine using strict categorization

Answer 11

• traditionally thought in terms of diagnoses and treatment
• if a patient has a disorder they are prescribed a treatment or not

Question 12

example: depression

Answer 12

each symptom in the DSM-5 has its own criterion (threshold) for if they symptom is present

Under the categorical approach, “normal” people may have measurable levels of depression but it is ignored

• dimensional approach: a person can show severity in unique patterns over time

Question 13

what are the two approaches

Answer 13

1. categorical model
2. dimensional model

Question 14

measurement error

Answer 14

• mis measurement is present to some degree in every single health assessment
• no measure can be perfect
• diff tools to measure reliability and validity for classification

Question 15

concordance

Answer 15

concordance measures the percentage of agreement between two sources

categorical variables (diseased/non diseased)

example: Use CES-D at a specific cut-off score to
classify as clinically depressed, compare findings to a diagnosis
- is the screener as reliable as the diagnosis

variance in the responses = reliability
- does not necessarily need to be against a “true” diagnosis
- seeing how often the pairs match values

Crude measure of reliability
- does not adjust for chance

Question 16

Kappa

Answer 16

most widely used measure of reliability in classification
- designed to adjust for chance
- the amount by which the observed concordance exceeds what is expected by chance
- dependent on prevalence

Po is the observed concordance
Pe is the concordance by chance

• normally they fall between 0-1, become negative when observed is less than expected

Question 17

difference bw concordance and Kappa

Answer 17

concordance measures percentage of agreement bw two sources - does not account for agreements that happen by chance

Kappa - more advanced that adjusts for chance measurements

Question 18

pearson & spearman correlation coefficient

Answer 18

Correlation coefficients measure the degree pairs of observations fall on a straight line (ranging from -1 to 1)

Pearson correlation is for continuous variables while the
Spearman rank correlation is for ordinal variables

Question 19

what is Intraclass Correlation Coefficient (ICC)

Answer 19

accesses the reliability of continuous measurements by analyzing the variance in scores

between person variance: how much people differ overall

within person variance: how much scores vary for the same person (ex. how diff they respond to the 2 surveys)

Question 20

What does it mean if test has ICC=1?

Answer 20

test = PERFECTLY RELIABLE

• all variability in scores is due to differences bw individuals, no inconsistencies in how individuals are measured

Question 21

What does it mean if a test has ICC=0?

Answer 21

NO RELIABILITY

• test scores are random and do not reflect consistent differences between individuals

Question 22

validity in health

Answer 22

reliant on criterion validity

primary tools for validity: sensitivity and specificity

In validity, we break apart this agreement into two components: positive agreement and negative agreement

Question 23

what is sensitivity

Answer 23

is the conditional probability that a true case is detected

The ability of a test to correctly identify true positives (e.g., detecting all people who have a disease).

High sensitivity = fewer false negatives.

Question 24

what is specificity

Answer 24

the ability of a test to correctly identify true negatives (e.g. people who do not have the disease

High specificity = fewer false positives

Question 25

should a test have both sensitivity and specificity?

Answer 25

High sensitivity and high specificity is desirable, but unrealistic

• The two cannot be considered in isolation when considering
  validity
• sensitivity and specificity of two measures can be compared
  in order to help decisions on measure selection