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Basic epidemiological principles in psychiatry and psychiatric rating scales. Sean Lynch. Research Methodology and Epidemiology - 2. Research Methodology and Epidemiology -2. This is the second part of the afternoon module and today we will look at some aspects of rating scales and theory

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basic epidemiological principles in psychiatry and psychiatric rating scales

Basic epidemiological principles in psychiatry and psychiatric rating scales

Sean Lynch

Research Methodology and

Epidemiology - 2

research methodology and epidemiology 2
Research Methodology and Epidemiology -2

This is the second part of the afternoon module and today

we will look at some aspects of rating scales and theory

In psychiatry

research methodology and epidemiology 21
Research Methodology and Epidemiology -2

Self-rated Scales

Quick, save interviewer time

Lack of bias

Reliable

Can be used for case detection

Can be used as outcome measures

Only as good as the questions they ask

Problems with phrasing, ease of reading, language

“Order effects”

“Social desirability effects”

“Central tendency”

research methodology and epidemiology 22
Research Methodology and Epidemiology -2

Self-rated Scales

Can be used for any diagnostic category, except arguably less well for psychosis, cognitive impairment

Can be used to study core symptom dimensions in depth e.g. sleep, energy

research methodology and epidemiology 23
Research Methodology and Epidemiology -2

Interview - Rated Scales

Can be used to help assess whether a mental disorder is present or not

Can be used to assess the severity of symptoms in a mental disorder

Can be used with a taxonomical system to make diagnosis

Can also be used to study certain dimensions of symptoms in great depth

Can be highly structured with pre-determined questions

Can be more flexible and allow more “open-ended” questions

research methodology and epidemiology 24
Research Methodology and Epidemiology -2

Interview - Rated Scales

Can be subject to observer bias

Different raters might disagree on assessment

Can be subject to changes in behaviour of the same rater over time

Can be flexible and obtain supplementary information

Probing questions can be used to ensure subject understand the questions

Some say these scales can be sensitive to “clinical change”

research methodology and epidemiology 25
Research Methodology and Epidemiology -2

Scales need to have an “anchor point” to distinguish between lack of pathology and an “extreme” to assess severe pathology

Scales can be broad and have numerous intermediate points with phrases or words to help guide scoring of severity or degree

Scales can be narrow and dichotomous

research methodology and epidemiology 26
Research Methodology and Epidemiology -2

Scales can suffer from “ceiling” and “floor” effects i.e. if measuring dimensions within less severe or more severe examples of pathology e.g. depressed mood.

It can be hard to show improvement in an item where there is not much opportunity to show change! e.g. trials in mild severity depression

research methodology and epidemiology 27
Research Methodology and Epidemiology -2

Properties of Scales

1. Case finding

Ability to detect “cases” (true positives)

Ability to distinguish “non-cases” (true negatives)

Performance on these with minimum of misclassification i.e. low false positive and low false negative

The fine tuning of a scale cut-off point or score can be biased towards sensitivity (true positives/true positives and false negatives) in other words not “missing” too many cases, or specificity (true negatives/true negatives and false positives) in other words having a lower number of

“non-cases” incorrectly identified as cases

research methodology and epidemiology 28
Research Methodology and Epidemiology -2

Properties of Scales

2. Assessing severity

Can less severe and more severe cases be separated by the scale?

Would similar scales or measures show agreement on severity?

3. Assessing change

Is a reduction or increase in score on the scale associated with changes in the clinical picture?

research methodology and epidemiology 29
Research Methodology and Epidemiology -2

Reliability

“It does what it says on the tin most times”

Test-retest

Inter-rater

Internal Consistency

research methodology and epidemiology 210
Research Methodology and Epidemiology -2

Validity

“It really tells you what is in the tin most times”

Convergent

Face

Construct

A scale can be highly reliable but measure such a narrow concept it is clinically meaningless i.e. not valid

research methodology and epidemiology 211
Research Methodology and Epidemiology -2

DEPRESSION RATING SCALES

Interview-rated

HAMILTON 17 and 21 item

MONTGOMERY ASBERG 10 item

Self-rated

HAD (Hospital Anxiety and Depression) 7 item

Beck (BDI) 21 and 13 item

research methodology and epidemiology 212
Research Methodology and Epidemiology -2

ANXIETY RATING SCALES

Interview-rated

HAMILTON 14 item

Self-rated

HAD (Hospital Anxiety and Depression) 7 item

research methodology and epidemiology 213
Research Methodology and Epidemiology -2

OBESSIONAL RATING SCALES

Interview-rated

Y-BOCS (Yale Brown) 10 item

Self-rated

OCI (Obsessive Compulsive Inventory) 42 item

research methodology and epidemiology 214
Research Methodology and Epidemiology -2

SCHIZOPHRENIA RATING SCALES

Interview-rated

PANSS

SANS

SAPS

BPRS

research methodology and epidemiology 215
Research Methodology and Epidemiology -2

MANIA RATING SCALES

Interview-rated

YOUNG MANIA RATING SCALE

research methodology and epidemiology 216
Research Methodology and Epidemiology -2

DIAGNOSTIC INTERVIEWS

SCAN (Wing et al ) - ICD

SCID - DSM

research methodology and epidemiology 217
Research Methodology and Epidemiology -2

Disease concepts for diagnosis

Competing paradigms were reductionist or more pragmatic and multidimensional

Hierachical approach (Foulds)

Multiaxial approach (DSM)

Now concepts of subsyndromal disorder

levels of psychological disturbance severity
Levels of psychological disturbance - severity

Normal distress

Monosymptomatic - but recognisable

Subsyndromal - collection of several symptoms which fails to meet diagnostic criteria

Syndrome

other qualifying criteria
Other qualifying criteria

Frequency and persistence of symptom

Functional impairment or disability

Symptom duration

factors affecting agreement on diagnosis
Factors affecting agreement on diagnosis

Can have the same information but different disease concepts

Can evaluate the same information in a different way

Can elicit different information from the same patient

Can have changes in the clinical condition of the patient at different times

factors affecting agreement on diagnosis1
Factors affecting agreement on diagnosis

Different raters have different levels of knowledge and expertise e.g. differences between primary and secondary care

Our diagnoses have a degree of inbuilt uncertainty

How confident are we that our diagnosis is right?

How often will our colleagues agree with us?

agreement on diagnosis case example
Agreement on diagnosis - case example

Man of 40 who presents to GP

Insomnia for ten days

Panic attacks for three weeks

Irritability at work for two weeks

Reduced libido for ten days

agreement on diagnosis case example1
Agreement on diagnosis - case example

Man of 40 who presents to GP

Insomnia for ten days

Panic attacks for three weeks

Irritability at work for two weeks

Reduced libido for ten days

Hopelessness about future (week)

Appetite reduced (two weeks)

Reduced energy (two weeks)

agreement on diagnosis case example2
Agreement on diagnosis - case example

BUT has auditory hallucinations in third person for three days!

agreement on diagnosis
Agreement on diagnosis

What is a psychiatric case? “Gold standard” - Kendell, Shepherd

Inter-rater reliability

Intra-rater reliability

Diagnostic interviews and index of definition

“Cut-offs” based on symptom severity on rating instruments

Computerised

agreement on diagnosis1
Agreement on diagnosis

Generally improved with more severe illness

Difficulty in milder illness levels distinguishing from the normal range

More difficult for certain diagnostic concepts e.g. personality disorder and new DSM V

usefulness of diagnosis
Usefulness of diagnosis

Categorical verus dimensional models of illness

Hypertension is not “all-or-nothing” but spectrum form obvious disease to normal range

Rose “not important if he has it, the question is how much of it he has”

Bentall - distribution of psychotic symptoms

prevalence
Prevalence

The number of defined cases of disease in an area

Includes older and more recently diagnosed cases

Can be influenced by the chronicity of illness more than the incidence of illness

Cases can develop and remit (or die) and influence prevalence

prevalence1
Prevalence

Point prevalence

Period prevalence

“Life-time rates”

prevalence interpreting changes
Prevalence - interpretingchanges

Can be due to true changes in incidence

Can be due to changes in effectiveness of interventions

Can be due to changes in nature or course of illness

Can be due to changes in detection rate

incidence
Incidence

The number of new cases of illness in an area over a period of time

Changes more likely to reflect influences on causation or associated risk

Does not in itself give information on total number of cases in community

Changes can be due to changes in detection rate

Problem of including relapses inadvertently

incidence1
Incidence

Diseases with low incidence can become prevalent in community if chronic illnesses

Prevalence can change without change in incidence necessarily e.g. change in severity of illness or effectiveness of treatment

methods to assess incidence and prevalence
Methods to assess incidence and prevalence

A case register to document all contacts over

a defined period

“Observatory” method

Case notification methods

Population based studies

methods to assess incidence and prevalence1
Methods to assess incidence and prevalence

These methods can have limitations in diseases with low incidence rates and prevalence rates

The first three methods are particularly prone to error if there are problems (or there is not full consensus) on the case definition

The detection rate of cases should also be measured to assess accuracy (against best available standards)

methods to assess incidence and prevalence2
Methods to assess incidence and prevalence

Case ascertainment methods

Prodromal phases

Changes to case definition

Need to have reliable and valid raw data to review estimates

methods to assess incidence and prevalence3
Methods to assess incidence and prevalence

Other problems in psychiatry:-

“Diagnostic overlapping”

Cultural influences on case ascertainment

Co-morbidity

Diagnostic stability over time

Social changes (“pathoplastic”)

methods to assess incidence and prevalence4
Methods to assess incidence and prevalence

“Head count” methods in psychiatry:-

Case notification depends on accuracy of diagnostic assessment and health seeking behaviour

Case registers depend on capturing all cases and do not cope well with migration effects and changes to housing or centres of population

methods to assess incidence and prevalence5
Methods to assess incidence and prevalence

Survey methods in psychiatry:-

Need to carefully define area studied

Feasible methods of case detection

Often expensive as need to cover large areas and numbers

Need to have accurate estimate of population base

methods to assess incidence and prevalence6
Methods to assess incidence and prevalence

Survey methods in psychiatry:-

Catchment area and “house to house” methods

Telephone methods

For less prevalent conditions and low incidence conditions will need to screen a large number of “normals”

Need a socially acceptable screening tool

methods to assess incidence and prevalence7
Methods to assess incidence and prevalence

Survey methods in psychiatry:-

Much more problematic for more severe illness

Problems of selection bias e.g. “cold-spots” of participation, wrong time of day

methods to assess incidence and prevalence8
Methods to assess incidence and prevalence

Other methods

Postal questionnaire

Two-stage screening

Representative sample e.g. random selection as per some marketing approaches

Quota samples

Convenience samples

Consecutive attendances

methods to assess incidence and prevalence9
Methods to assess incidence and prevalence

Error rate in study has to be defined.

Common methods:-

Reference to “gold standard”

With reference to known reliability and stability of case definition

Random resampling

Non-participation and non-completion rates

Estimates of “double counting” or “missing” cases

causation
Causation

Confounding variables

“Latent” variables

Interactions

Protective factors

Causative factors

causation1
Causation

Consider the following hypothesis:-

The risk of lung cancer is 100 times higher in

men aged 30-35 who smoke than in non-smokers.

Smokers on average watch 50% more television than

non-smokers. Smokers watching only the average

amount of television of non-smokers could reduce their

risk of lung cancer by one third. Television might also be

a causal factor in lung cancer.

causation2
Causation

Is there an argument to support this conclusion?

Is the evidence convincing?

Can you see any flaws in this argument?

Are there alternative methods of studying the

causal relationship between smoking, television

viewing and lung cancer?

exposure and risks
Exposure and risks

Case control method is classical method

It gives an indication of differences in the rate of

disease on exposure to a potential risk factor

Cross-sectional studies only give information on

association

Longitudinal studies give some more information

on causation

Exposure or “at risk” studies give the best quality

information

exposure and risks1
Exposure and risks

There are several assumptions:-

An equal chance of exposure to a risk factor in all the population?

Controls are “normal”

We can measure the level of risk or exposure

Exposure levels might vary in intensity

Duration of exposure might be relevant

exposure and risks2
Exposure and risks

Risk measures:-

These attempt to quantify the increase in the

number or proportion of cases in a population

exposed to the risk factor, compared to those not

exposed

Odds ratio

Relative risk ratio

Attributable risk

exposure and risks3
Exposure and risks

These are quite useful concepts but rely on assessing one risk factor at a time

In psychiatry multiple risk factors might be expected. Sometimes it is as useful to assess interaction between factors

We will discuss multivariate models in later sessions

ebm terminology
EBM terminology

Adverse event CONTROL TREATMENT

YES a b

NO c d

pc = proportion of controls with adverse event

pc= b/ (b+d)

pt = proportion of treatment group with adverse event

pt = a/(a+c)

Relative risk of event RRe = pt/pc

Relative risk of no event or RRne =(1-pt/ 1-pc)

ebm terminology1
EBM terminology

Odds ratio (OR) - (a x d) / (b x c)

Relative risk reduction RRR = (pc-pt)/ pc + 1-RRe

Absolute risk reduction (ARR) / risk difference (RD) = pc-pt

Number needed to treat NNT

NNT (risk difference) = 1/RD

NNT (relative risk of event) = 1 / (pc x RRR)

NNT (relative risk of no event) = 1 / (1-pc) x (RRne-1)

NNT (odds ratio) = (1-(pc x (1-OR)) / (pc x (1-pc) * (1-OR))

other important related concepts
Other important related concepts

We will discuss these more fully when

discussing rating scales

Sensitivity

Specificity

Misclassification rate

Predictive value

Efficiency