In the literature, there is often a description saying that ''an animal weight X to Y grams/pounds was used''. I was wondering how do the author know the best weight range of their experimental animals?
Sorry for the naive question but I really need the answer.
Thank you very much in advance!
Selecting animals within a certain weight range may introduce bias in the experiment. Any healthy animal that is within the specified age range should be eligible for the experiment. Choosing animals in a narrower range than is the normal distribution for the population introduces a bias. It is best to utilize the full range of sizes and metabolic weights that are represented within the potential population for a specific age range. Extrapolation from an artificial weight range may not represent the same response that would occur if one used the entire weight spectrum of the population. Be careful to avoid biasing your experiments.
I think to the best of my knowledge, for most of the experiments we require healthy young, adult animals. On the basis of these criteria we screen animals for experiment. We generally find the best weight of animal about these criteria only.
For example - I use male adult sprague dawley rats for experiment. Proper male adult sprague dawley rats has weight 220-230 grams. Hence we consider this weight is for screening our animals.
Hi Ping,
From the weight and animal species described, you can actually know the age of the animals that were used. For whatever animal you work with, there will be an weight/growth chart. simply, weight description = age description for that particular strain - note that male and females are different. Your choice of the age/weight depends on your questions and technical approaches. You have to search for the developmental stages for the species/strains you work with. And if you use very young animals, you have to consider whether what you want to study is fully developed in the animal. Thus, all comes down to your scientific questions and the limitations you have with the techniques you use.
Selecting animals within a certain weight range may introduce bias in the experiment. Any healthy animal that is within the specified age range should be eligible for the experiment. Choosing animals in a narrower range than is the normal distribution for the population introduces a bias. It is best to utilize the full range of sizes and metabolic weights that are represented within the potential population for a specific age range. Extrapolation from an artificial weight range may not represent the same response that would occur if one used the entire weight spectrum of the population. Be careful to avoid biasing your experiments.
It's just a range of the animal weight from their experience. The breeder may not be able to provide you with the exact weight for each request. Therefore you can demand for a certain range, e.g. 180-200g for adult rats. In that case, the breeder has to document your needs and making sure the weight doesn't fall below 180g.
Most scientists try to minimize the variability in their experiments by using "exactly" the same thing over and over. This is based upon a false assumption that you can only change one thing at a time during an experiment. This has never been true and is actually the opposite of what a good experiment should do.
As a statistician, I would use weight and gender of the animal in my analysis of the effects. I might even look at effect of diet on the results too. As Jack stated, by looking at only "select" subjects, you will bias your results, possibly to the point of uselessness. Test male and female subjects of different weights and body fat. Then use multiple logistic regression in your analysis.
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