It is only when you are working with rodents you have to abstain from using females because their estrus cycle disturbs the results.

If you want to increase your study external validity and enhance your study resutls generalizability you need a more heterogeneous sample that includes both genders unless you are targeting specific factors (i.e., gender differences).

Thanks s. Béatrice Marianne Ewalds-Kvist

Most of the times and in specific hormonal, endocrinological and behavioral studies the cycle and thus using only male subjects can be the case. But it does not mean to "abstain" from using female groups.

There are many outstanding studies that used female subjects, rats for instance to investigate the role of certain hormones on behavior. Our new publication is about the effects of oxytocin administration on male risky behavior, though there are studies on the effect of oxytocin or vasopressin on female rodents' maternal behavior, for example:

https://science.sciencemag.org/content/216/4546/648

Or regardless of some gender-specific behaviors, there are studies on both genders in both sexes of rodents in just one study as a comparative model:

https://psycnet.apa.org/record/2008-03846-007

http://jpet.aspetjournals.org/content/340/3/801.short

Thanks Hassan Izzeddin Sarsak

Validity and probity of a study depends on a wide ranging critical parameters of statistical, analytical, experimental and replicability of the study under any circumstances.

As the statistical analysis and experimental design of a study can be replicated there are disparate factors such as environmental situation, gene-specific expression of phenotype and behavior or even differences in preparation and administration of certain treatments under certain circumstances that preclude the results of apparently similar studies to be generalized.

Mutability of results of biological and medical studies and the need for updated followup investigations every now and then to check the validity of results under changeable biological and environmental conditions just avoid us from generalizing the results. Generalization of results can be translated into bias in a study due to the different variables from subjects to concentration and dosage of drugs, animals and animal room situation, and most importantly epigenetic factors.

Meanwhile, heterogeneous samples are not often desirable because of the problematic extent of variability which they exert in results, leading to less reliable statistics.

Heterogeneity in medical and biological research in terms of comprehensiveness can be achieved by including different control and treatment groups for a population to analyze all possible circumstances in a comparative mode to eliminate bias.

Inclusion of both genders in separate groups to be studied in one investigation definitely can seem futile when focusing on gender-specific factors. This seems rather counterintuitive, but check the following example.

A very famous example can be seen in breast and ovarian cancers in which the genes can be passed to children from fathers without any sign and be expressed as a gender-specific cancers in daughters.

Men are just similar to women to have an aberrant breast cancer gene (BRCA1 and BRCA2). If they have an abnormal gene, men are also just as likely to pass it on to both their daughters and their sons.

Men with an abnormal BRCA1 or BRCA2 gene are 80 times more likely to develop breast cancer than men who don't have an abnormal gene. Breast cancer in men without an abnormal gene is rare.

So a woman who has a strong family history of breast or ovarian cancer on her father's side (her dad's mother or sisters) has the same risk of having an abnormal breast cancer gene as a woman with a strong family history on her mother's side.

Still, a study suggests that women are much more likely to be referred for genetic counseling if the family history of breast or ovarian cancer is on their mother's side rather than their father's.

This could mean that doctors aren't recognizing that paternal (father's) family history of breast and ovarian cancer is equally important as maternal (mother's) family history when considering abnormal breast cancer gene risk. It's also possible that women themselves don't consider paternal family history equal to maternal family history when talking about risk and family history with their doctors.

https://www.breastcancer.org/research-news/20101024

Any comments?

We have been into aggression research and female mice do not display aggression in the same way as males do.

Interesting!

In this case, aggression in male rats probably is due to the sense of dominance, territory seeking, etc.

Besides the plexuses of hormonal interactions, as far as I know, aggressive behavior is interrelated with changes in serotonergic system.

This could also be a great topic in this discussion to see how the possible lack of serotonin transporters may conceivably reduce aggression.

This depends on the type and purpose of the study and the type of sample being studied

Greetings

The aggression in mice were explained in other terms but we were not allowed to call it aggression in humans but hostility. When we did vasectomy, we used only males for natural reasons and when we studied hysterectomy we used only females for as well natural reasons. We though tested their biological sex and psychological gender but our patients were not gender dysphoric so there was no problem.