Dear Fu,

You should include a healthy mice group to see the side effects that might result from the use of a drug.

This step is a mandatory when you apply a drug to the FDA (however, in this case you carry out the test on healthy people).

The following link may be helpful when you conduct a study on animals:

http://www.ncbi.nlm.nih.gov/books/NBK84204/

Hoping this will be helpful,

Rafik

Dear Fu,

You should include a healthy mice group to see the side effects that might result from the use of a drug.

This step is a mandatory when you apply a drug to the FDA (however, in this case you carry out the test on healthy people).

The following link may be helpful when you conduct a study on animals:

http://www.ncbi.nlm.nih.gov/books/NBK84204/

Hoping this will be helpful,

Rafik

Dear Fu Shun,

It was many years ago, in the late 1970s, when they’ve come to conclusion that not WHY but rather HOW to include a healthy (control) group, for instance, in vivo studies of 3,4-benzpyrene induction of CYPA1-catalyzed hepatic 3,4-benzpyrene hydroxylation using murine model. In a nutshell, many such studies in the labs all over the world were compromized by the lately discovered fact that scientific vivariums of those times did not protect mice of control group from their hepatic benz(a)pyrene hydroxylase being pre-induced by tobacco smoke, which contains 3,4-benzpyrene, and even from traces 3,4-benzpyrene as a constituent of polluted urban air. So, control benz(a)pyrene hydroxylase was always at the level elevated than it has to be, and experimental results did not reflect the effect of the induction. It took a while to reconstruct all vivariums in order to meet the above challenges thus preventing falsified results in the forthgoing experiments on the dynamics of chemical carcinogenesis in mammals, namely, pathogenesis of hepatic and pulmonary neoplasia.

Best wishes,

Ilya

You always need a suitable control group. Whether that control group needs to be "healthy" or not depends on the objective of your animal trial. From the limited information you have provided, I wonder why you would need two control groups - one of tumour-induced mice, and one of non-induced mice. I mean, you might need the healthy group, but it depends on what you are trying to find out. (I don't necessarily agree with Rafik that all studies should have a healthy control group - simply because not all studies are investigating side-effects or are being conducted for licensing purposes.)

Dear Paul,

An answer to your comment can found in the following text taken from a paper which its link placed at the end of the text:

N Factor: Experimental Group Size

The assignment of an appropriate number of animals to each group is critical. Although formulas to determine the proper number of animals can be found in standard statistical texts, we recommend consulting a statistician to ensure appropriate experimental design for the generation of statistically significant results (Zolman 1993). Indeed, the number of animals assigned to each experimental group is often determined by the particular statistical test on the basis of the anticipated magnitude of difference between the expected outcomes for each group. The number of animals that can be grouped in standard cages is a practical consideration for determining experimental group size. For example, standard 71 sq in (460 sq cm) polycarbonate shoebox cages can house up to four adult mice, so group sizes that are divisible by four will maximize group size and minimize per diem costs.

Controls

A plethora of variables (e.g., genetic, environmental, infectious agents) can potentially affect the outcome of studies performed with animals. It is therefore critical to use control animals to minimize the impact of these extraneous variables or to recognize the possible presence of unwanted variables. In general, each individual experiment should use control groups of animals that are contrasted directly to the experimental groups of animals. Multiple types of controls include positive, negative, sham, vehicle, and comparative.

Positive Controls

In positive control groups, changes are expected. The positive control acts as a standard against which to measure difference in severity among experimental groups. An example of a positive control is a toxin administered to an animal, which results in reproducible physiological alterations or lesions. New treatments can then be used in experimental groups to determine whether these alterations may be prevented or cured. Positive controls are also used to demonstrate that a response can be detected, thereby providing some quality control on the experimental methods.

Negative Controls

Negative controls are expected to produce no change from the normal state. In the example above, the negative control would consist of animals not treated with the toxin. The purpose of the negative control is to ensure that an unknown variable is not adversely affecting the animals in the experiment, which might result in a false-positive conclusion.

Sham Controls

A sham control is used to mimic a procedure or treatment without the actual use of the procedure or test substance. A placebo is an example of a sham control used in pharmaceutical studies (Spector 2002). Another example is the surgical implantation of “X” into the abdominal cavity. The treated animals would have X implanted, whereas the sham control animals would have the same surgical procedure with the abdominal cavity opened, as with the treated animals, but without having the X implanted.

Vehicle Controls

A vehicle control is used in studies in which a substance (e.g., saline or mineral oil) is used as a vehicle for a solution of the experimental compound. In a vehicle control, the supposedly innocuous substance is used alone, administered in the same manner in which it will be used with the experimental compound. When compared with the untreated control, the vehicle control will determine whether the vehicle alone causes any effects.

Comparative Controls

A comparative control is often a positive control with a known treatment that is used for a direct comparison to a different treatment. For example, when evaluating a new chemopreventive drug regime in an animal model of cancer, one would want to compare this regime to the chemopreventive drug regime currently considered “accepted practice” to determine whether the new regime improves cancer prevention in that model.

Randomization

Randomization of the animals assigned to different experimental groups must be achieved to ensure that underlying variables do not result in skewed data for each experimental group. To achieve randomization, it is necessary to begin by defining the population. A homogeneous population consists of animals that are considered to share some characteristics (e.g., age, sex, weight, breed, strain). A heterogeneous population consists of animals that may not be the same but may have some common feature. Generally, the better the definition of the group, the less variable the experimental data, although the results may be less pertinent to large broad populations. Methods commonly used to achieve randomization include the following (Zolman 1993):

Identifying each animal with a unique identification number, then drawing numbers “out of a hat” and randomly assigning them in a logical fashion to different groups. For example, the first drawn number is assigned to group 1, the second to group 2, the third to group 1, the fourth to group 2, and so forth. Dice or cards may also be used to randomly assign animals to experimental groups.

Using random number tables or computer-generated numbers/sampling to achieve randomization.

http://ilarjournal.oxfordjournals.org/content/43/4/202.full

Rafik

Ah yes, as a negative control, of course. Good point! In toxicology, for testing e.g. endocrine disruptors, we would use negative controls to ensure the test species was (for example) actually responsive to the hormonal change the researchers believe they may be inducing. I'm still not sure that necessitates a "healthy" control group, however - the control still needs to be appropriate, and I would resist a priori generalisations as to how that appropriateness ought to be defined.

Thank You All so Much... Very informative

Normal healthy animals are used  to avoid the variations and baseline or historical data of the test facility would also help in better interpretation on the outcome of toxicity profile, if observed.