It depends on which science.
In social, behavioral, industrial, and many health related fields, the
distinction is sharply drawn between true experiments where there is active
manipulation of one or more treatment independent variables and random
assignment of cases to treatment. (also, it simplifies calculation and drawing
conclusions if there are equal n's in cells of the design.)
Other designs are considered quasi-experimental where plausible rival
hypotheses need to be addressed by considerations other than manipulation and
random assignment. The fewer aspects of a true experiment a study has the more
discussion there needs to be of ruling out the rival hypotheses. The study you
briefly describe would be called quasi-experimental.
Some fields in statistics talk about what other fields would consider "thought
experiments" such as ball-and-urns as experiments.
The term "observation" has a wide variety of meanings, but some would include
several kinds of quasi-experimental designs as observational
- - -
in your quasi-experiment you can possibly contrast different levels of specific
pollutants, as well as kinds of pollutants, in different rivers at different
times.
I'm not a biologist, but I would be amazed if temperature did not affect
population sizes.
.
Voltolini wrote:
> Hi,
>
> I was reading a definition of "experiment" in science to be used in a
> lecture and the use of treatments and controls are an important feature of
> an experiment but.... my doubt is... is it possible to plan an experiment
> without a control and call this as an "experiment" ?
>
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