1.
In an observational study you are not giving the subjects any type of treatment;
you are just recording what you observe.
In an experiment, you are giving the
subjects a treatment and observing the effects of that treatment.
2.
A retrospective study is an observational study in which you look at past data.
Typically used when you are studying something that is unethical (such as
drinking during pregnancy).
A prospective study is an observational study in
which you observe over a significant period of time.
This is used when you want
to study long term effects.
3.
retrospective studies are usually unable to reach cause-and-effect conclusions. For
example, we cannot conclude that physiotherapy definitively improves RTW
outcomes among back-injured workers. This is because of
confounding factors.
4.
Considered the gold standard of study design, are prospective studies. They can
provide evidence of cause-and-effect relationships and support changes in clinical
practice or workplace interventions. In a randomized controlled trial, subjects are
randomly assigned to receive the intervention or control treatment, and outcomes
are evaluated after the intervention period.
5.
Definitions
a.
Control:
An experiment that isolates the effect of one variable on a
system by holding constant all variables but the one under observation.
b.
Replicate:
is the repetition of an experimental condition so that the
variability associated with the phenomenon can be estimated.
c.
Randomize:
is the process of making something random; this means:
i.
Generating a random permutation of a sequence (such as when
shuffling cards).
ii.
Selecting a random sample of a population (important in statistical
sampling).
iii.
Generating random numbers: see Random number generation.
iv.
Transforming a data stream (such as when using a scrambler in
telecommunications).
d.
Block:
is the arranging of experimental units in groups (blocks) that are
similar to one another. For example, an experiment is designed to test a
new drug on patients. There are two levels of the treatment,
drug
, and
placebo
, administered to
male
and
female
patients in a double blind trial.
The sex of the patient is a
blocking
factor accounting for treatment
variability between
males
and
females
.
This
preview
has intentionally blurred sections.
Sign up to view the full version.

This is the end of the preview.
Sign up
to
access the rest of the document.
- Spring '12
- Dyer
- Randomness, omega-3 fats
-
Click to edit the document details