Measurements and Errors of measurement/Data source & Quality Flashcards
Defining who has the disease
PROBLEMS WITH INCIDENCE AND PREVALENCE MEASUREMENTS:
PROBLEMS WITH NUMERATORS
.Problems due to difficulties in diagnosis
Some Possible Sources of Error in Interview Surveys
- participant may chose not to respond or alter his response
- responds to please the interviewer
Problems associated with the study participant
- not recording or incorrect recording
- incorrect questioning
- biased by knowing the hypothesis being tested and may probe more intensively in one group than in another
Problems associated with the interviewer
- Selective undercounting of certain groups e.g. Ethnic minority
- Different studies use different definitions so comparison of results is difficult
- For a rate of make sense, every one in the group represented by the denominator must have the potential to enter the group represented by the denominator. This is not that simple.
Example: Uterine cancer rates
Hysterectomy
PROBLEMS WITH DENOMINATORS
An index of the severity of a disease from both clinical and public health standpoints
Mortality
Can also be used as an index of the risk of disease
Mortality
Easier to obtain than incidence data for a given disease, however when a disease is mild and not fatal, it is not a good index for incidence
Mortality
2 conditions where mortality rate is a good reflection of incidence rate:
When case-fatality is high (i.e. untreated rabies)
When duration of disease is short (survival)
i.e Pancreatic cancer – where mortality is good surrogate for incidence
the disease or injury which initiated morbid events leading directly or indirectly to death → underlying cause
Cause of death
excludes information pertaining to the immediate cause of death, contributory causes, and those causes that intervene between underlying and immediate causes
Underlying cause of death
Is a true experiment in which patients are assigned randomly to a study category (treatment), and are then followed forward in time, and the outcome is assessed
RANDOMIZED CONTROL TRIAL (RCT)
meaning the sample members are allocated to treatment groups by chance alone so that the choice reduces the risk of possibly biasing factors
RANDOMIZED CONTROL TRIAL (RCT)
- lack of representativeness
- “a process at any stage of inference tending to produce results that depart systematically from the true values”
BIAS
Occurs when two factors are associated with each other and the effect of one is confused with or distorted by the effect of the other
CONFOUNDING BIAS
are factors (exposures, interventions, treatments, etc) that explain or produce confounding
Confounder
- Creates problems in statistical analysis
- Affects comparability of treatment and control groups
Problems with Sample Attrition
Treatment maybe so effective that patients believe themselves to have been cured and cease taking medications; successes disappear from treatment, leaving treatment appearing less effective than what it really is
Problems with Sample Attrition
- Replacement of drop-outs not advisable
- Drop-out rates should be considered in sample size estimation
Problems with Sample Attrition
indicator of therapeutic usefulness and effectiveness and should be considered when drawing conclusions from trials
Drop-out data can be used
the extent to which a measurement or study reaches the correct conclusion.
VALIDITY
The degree to which a test is capable of measuring what it is intended to measure
VALIDITY
The degree to which the result of an observation are correct for the particular group studied
INTERNAL VALIDITY
determined by how well the design, data collection, and analyses are carried out and are threatened by all the biases, and random variation
INTERNAL VALIDITY
Extent to which the study’s results can be applied to those beyond the study sample
EXTERNAL VALIDITY (Generalizability)
Assuming that the results of the study are true, do they apply to my patients as well?
EXTERNAL VALIDITY (Generalizability)
expresses the validity of assuming that patients in a study are comparable with other patients
Generalizability
Due to differences or changes in the standardized diagnostic criteria
(i. e. diagnostic custom) used by most physicians
- example: Hypertension, Rheumatoid arthritis
THE OBSERVER
Due to differences or changes in the application of diagnostic criteria by individual clinician
example: rounding off quantitative measurements (BP), carelessness, or simple ignorance
THE OBSERVER
International Classification of Diseases, 8th revision – reported a 15% increase deaths due to IHD ICD 9th revision reported reduced number of death
THE SYSTEM used for codifying and classifying observations of the phenomena of interest
Errors due to behavioural responses
Example:
- Recall bias
- Response bias
- Response-set bias (strongly agree; strongly disagree
THE SUBJECT being examined, interviewed or observed
the interviewer tends to elicit a desired or expected response by wording a question in certain way
Experimenter bias
the subject’s experience or knowledge that he is being observed or studied changes his behaviour or performance, and possibly certain physiologic functions – Placebo effect
Hawthorne effect
Temporary elevation of BP due to anxiety
THE SUBJECT
Errors due to mechanical failures or problems with equipment
THE INSTRUMENT used for making measurements or combining information
Errors due to conceptual problems involving the availability or adequacy of specific tests
THE INSTRUMENT used for making measurements or combining information
Errors due to analytic or scaling problems of combining from two or more items or tests to form an overall index or indicator of the factor (disease) of interest
Example: combining different scores from survey stems, clinical symptoms or lab tests to derive an index of depression
THE INSTRUMENT used for making measurements or combining information
- Human errors of data processing
- encoding, key punching, data abstraction and transcription, improper use of computer software, and bugs and viruses in the software
THE DATA PROCESSING EFFORT
the extent to which a measure produces the same result at different times for the same subjects
INTRA-OBSERVER RELIABILITY
- the extent to which a measure produces the same observation on each subject regardless of who makes the ob
INTER-OBSERVER RELIABILITY
- the extent to which all items or test making up a composite measure (index) reflect the same underlying construct
INTERNAL CONSISTENCY
those obtained by the investigator to answer specific questions he has in mind
PRIMARY DATA
- interviews, PE, laboratory tests
- more expensive and more difficult to obtain but more accurate and up-to-date
PRIMARY DATA
- those that are actually gathered by other individuals/investigators
SECONDARY DATA
- already published reports or existing records from agencies or institutions
SECONDARY DATA
- more readily available but maybe incomplete
SECONDARY DATA
may be difficult to access because of confidentiality of data
SECONDARY DATA
Define the population at risk
Census statistics
DENOMINATOR DATA
- Define the events or conditions of concern
- Statistics from health, disease, birth, and death registries and surveys
NUMERATOR DATA
- Natality, mortality, marriages, divorces, adoptions
- Total births/deaths, deaths by specific cause, infant mortality, etc
DATA ON VITAL EVENTS
- Existence of disease based on abnormal PE and/or laboratory findings
- Prevalence or incidence of specific diseases
DISEASE STATISTICS
Hemoglobin, blood sugar levels, blood pressure
Data on physiologic &/or pathologic conditions
Activities and performance of health agencies
Data on health resources and service
. Number of households with sanitary water source; amount of pollution in the air; noise level
Statistics pertaining to the environment
Total number of people in an area according to age, gender, urban
Demographic data
. KAP of people regarding health practice
Socio-cultural data
required to be registered within ____ days by birth attendant or the family or any person who knows the occurrence of the event, at the Local Civil Registry
Birth: 30 days
Uses of Birth Certificate
1 To prove the fact of birth
-For proving parentage; for inheritance of properties;for settlement of insurance; for legal dependency; to establish identity; for tracing ancestry; for planning child health programs
2 To prove date of birth
- For entrance to school, automobile license; right to vote; for marriage; for entering civil service, social security benefits; settlement of pensions; enlistment to armed forces; issuance of professional licence; proof of legal age
3 To prove place of birth
-For issuance of passport, immigration and to establish citizenship
Patters of fertility
Population estimate – based on the knowledge of births, deaths, and migration
Population projection
Public Heath Programs
Who can file the birth certificate?
Parents
Legal guardian
Midwife/ Physician
In case of a lost baby (foundling), the rescuer or founder
Required by law to be registered by medical attendant, family, local health officer, or anybody who knows such event
Death
Some aspects of person’s death are not reflected
circumstances of death
It should be filed within _____ after the time of death
48 hours
Uses of Death Cartificates
1 To prove the fact of death
- For lifetime insurance claims and for settlement of estates
2 To prove facts about the deceased for circumstances of death
- For access to or termination of government services such as health cards, pensions, etc
- For medical, health research and for statistical purposes
- To provide an ongoing mortality data resource for measuring health problems, guiding health programs, and evaluating health promotions and disease control activities
Cause of Death
The disease or injury that started the physiological processes that led to the termination of life
Disease or injury that led to the death
Ex: Pneumonia
Immediate Cause of Death
Pertains to the sequelae or complications that gave rise to the immediate cause
Ex: Stroke
Antecedent Cause of Death
> Root disease; other significant conditions contributing to death but not actually related to the immediate cause; most important of the three
Ex: Diabetes Mellitus
Example: A patient has diabetes mellitus. He then had a cerebrovascular accident and was hospitalized because of this. While in the hospital, he developed pneumonia and died.
Underlying Cause of Death
- Special records kept for special diseases, usually chronic, like cancers
- Should contain all cases of the illness that occur in the catchment area
- Contains pertinent information on the course of the illness, medications, etc
- One look at the register will tell how many prevalent cases are there, how many have died or recovered
Disease Registers
List of Notifiable Diseases by the DOH
Required by law to report to DOH
Attending physician
Maybe undernotified because of
> Ignorance of the law
> Non-caring attitude to report the case
> Not all sick people seek medical help
Disease Notifications
Taken at regular interval of years provide complete enumeration of population’s profile
Census
Sources of data in instances where the investigator need specific variables in specific scales of measurement
Surveys
Is the data available not long after the date of occurrence of the event covered?
Data is not often submitted on time because:
a. Health worker has too much work b. Too many forms to be filled up c. Transportation and communication problems
TIMELINESS
both completeness of coverage and completeness in accomplishing all the items in every form
Q: Does the data cover the entire geographic area and target population?
COMPLETENESS
refers to how close the measurement of the data is to its true value
ACCURACY
refers to the repeatability or consistency of the information
PRECISION
