Topic 2 Flashcards
What is a variable?
Types?
Any entity that can take on different values
Independent and dependant variable
EG indépendant variable = SMT
dependant variable- disability or pain
What is a natural history study and when would you use something like it?
The course of a disease from onset to resolution
Stages are as follows:
A. Stage of pathological onset
B. Pre-symptomatic stage: from onset to the first appearance of symptoms or signs
C. Clinically manifest of disease, which may progress inexorably to fatal termination
Detection and intervention may alter the natural history of the disease
Ex of Natural History- Sciatica
Stage 1- could be silent internal disc disruption form a degenerative process
Stage 2- may manifest as low back pain
3- Full blown leg pain which may regress spontaneously over weeks and then in some cases relapse with time.
Disease Frequency and Descriptive studies
Disease frequency studies quantify the occurrence of a disease
for this we need a numerator and a denominator e.g. cases studied
-can put this in terms of incidence or prevalence. “Rates”
Incidence and prevelance
Incidence is the no of new cases per unit in time
prevalence which is no. of cases present at a particular time or time interval
e.g. slide 9
Descriptive studies
what is it and what are the 3 main types?
Descriptive studies describe patterns of disease occurrence in relation to variable such as person, place and time
There are 3 main types of descriptive studies:
a) Correlational studies, which consider patterns of disease among population
b) Case reports or case series; and
c) cross sectional surveys of individuals
Correlation studies
What is it?
What is its limitations?
These studies look at measures that represent characteristics of populations that are used to describe disease in relation to exposure. e.g. age or food consumption with obesity
Does correlation = association = causation
represented by correlation co-efficient (r) Can ve up to +1 or down to -1
Limitations:
-limited ability to link exposure with disease E.G
We cannot be certain which is the cause and which is the effect, as the correlational data is only supporting the idea that they are both occurring together.
What are case reports and what are they useful for?
Case report and case series describe the experience of a single patient or a group of patients with a similar diagnosis
-These types of studies the clinician identifies an unusual features of a disease or patient history, may lead to formulation of new hypothesis.
While case reports are useful for hypothesis generation they CANT be as valid statistical association or to demonstrate efficacy in therapy.
-commonly used for alerting a potential adverse event or provides an unusual diagnostic presentation
What is a cross-sectional study, what are they used for and give an example.
Whats their limitations?
Exposure and the disease of interest is assessed simultaneously.
They provide a snapshot in time of condition under review .
Eg national health surveys
Limitations:
Because there are a snapshot in time, we can’t determine the temporal sequence between exposure and outcome. Did the exposure precede or results from the disease.
Ecological Studies
A branch of epidemiology in which the units of analysis are populations or groups of people rather than individuals
Case-control studies
Odds ratio:
limitations to this type of study?
observational analytic investigation were subjected are selected on basis of whether they do (cases) or not (controls) have the disease or disorder in question.
Cases are mostly uncommon and are selected. Then match to controls for comparison.
This type of study is retrospective- starts after onset of disease and looks back to causal factors
-statistically results in case-control studies quoted as Odds Ratio with Confidence intervals
Odds ratio:
The ratio of the odds of having the disorder in question if exposed to the factor in question/ (divided by) the odds of having the disorder if not exposed to the factor in question.
refer to slide 26
Limitations:
- retrospective study
- recall bias
- other factors may have intervened that were not controlled for.
- selection of controls may have produced a different group in some way (selection bias)
- hospital controls are often ill in some other way
- relying on medical records is fraud with danger
Cohort studies:
Relative Risk (RR)
Are another type of observational analytic study in which a group or groups of individuals are defined on the basis of of presence or absence of exposure.
- Follow up study
- subjects are followed ‘prospectively’ or forward in time.
- subjectes are exposed to the risk factor but don’t have the disease- overtime we see if it manifests
- usefull for rare exposures
- case-control studies were good for rare also memba.
view slide 36 for calculation
Experimental studies
What are the 3 types of clinical trials:
A Clinical trial is an experiment where individuals are randomly allocated to 2 or more groups. Known as experimental or control groups
-The experimental group given treatment and control is given shame treatment or placebo
- Therapeutic clinical trials:
- a therapeutic agent is given in attempt to relive or improve disease - Intervention clinical trials: Investigator intervenes before disease has developed in individuals with characteristics that increase their risk of developing disease/ disorder.
- Preventative Trials: an attempt is made to determine the efficacy of preventative agent or procedure
check out example on slide 42
Blinding: whats the different between: 1. Single blind study 2. Double blind study 3. Tripple blinding study
- In a single blind study, subjects are not given any indication whether they are in the experimental or control group. Usually achieved with placebo or sham treatment
- Double blinding: refers to single blinding PLUS the observer taking the data from the subject doesn’t know whether their in treatment or placebo group.
- Triple blinding
is double blinding PLUS the person analysing the data doesn’t know which group the subjects are in.
