Evaluation and Iteration

The scientific process is iterative. At any stage it is possible that some consideration will lead the scientist to repeat an earlier part of the process. For instance, failure of a hypothesis to produce interesting and testable predictions may lead to reconsideration of the hypothesis or of the definition of the subject.

It is also important to note that science is a social enterprise, and scientific work will become accepted by the community only if it can be verified. Crucially, experimental and theoretical results must be reproduced by others within the scientific community. All scientific knowledge is in a state of flux, for at any time new evidence could be presented that contradicts a longheld hypothesis. For this reason, scientific journals use a process of peer review, in which scientists’ manuscripts are submitted by editors of scientific journals to (usually one to three) fellow (usually anonymous) scientists familiar with the field for evaluation. The referees may or may not recommend publication, publication with suggested modifications, or, sometimes, publication in another journal. This serves to keep the scientific literature free of unscientific work, helps to cut down on obvious errors, and generally otherwise improves the quality of the scientific literature. Work announced in the popular press before going through this process is generally frowned upon. Sometimes peer review inhibits the circulation of unorthodox work, and at other times may be too permissive. The peer review process is not always successful, but has been very widely adopted by the scientific community.

The reproducibility or replication of scientific observations, while usually described as being very important in a scientific method, is actually seldom reported, and is in reality often not done. Referees and editors often reject papers purporting only to reproduce some observations as being unoriginal and not containing anything new. Occasionally reports of a failure to reproduce results are published - mostly in cases where controversy exists or a suspicion of fraud develops. The threat of failure to replicate by others, however, serves as a very effective deterrent for most scientists, who will usually replicate their own data several times before attempting to publish.

Sometimes useful observations or phenomena themselves cannot be reproduced. They may be rare, or even unique events. Reproducibility of observations and replication of experiments is not a guarantee that they are correct or properly understood. Errors can all too often creep into more than one laboratory.

Correlation and Causation

In the scientific pursuit of prediction and explanation, two relationships between variables are often confused: correlation and causation. Correlation refers to a relationship between two (or more) variables in which they change together. A correlation can be positive/direct or negative/inverse. A positive correlation means that as one variable increases, the other variable also increases and vice-versa. A negative correlation is just the opposite; as one variable increases, the other variable decreases and vice-versa.

Causation refers to a relationship between two (or more) variables where one variable causes the other. In order for a variable to cause another, it must meet the following three criteria:

1. The variables must be correlated.
2. One variable must precede the other variable in time.
3. It must be shown that a different (third) variable is not causing the change in the two variables of interest (spurious correlation).