This is a complicated topic. I think there are so many variables to achieve results. On the one hand, scientific studies, whether ethical or not, may prove things, if all control conditions are accepted - but do not necessarily lead to change in cage manufacture or education of owners.
So from your point of view maybe think about - do I want to improve conditions for hamsters, or do I want to prove scientifically that some conditions are harmful or cruel.
Sort of coming at it from different angles. As I said, it's tricky, because if you wanted to campaign heavily for change in cage manufacture and size and to educate people on living conditions, you need some authority to back up these claims. I don't think that has to be exactly scientific. For example - Panorama and other in depth programmes, make documentaries showing how something is cruel or unsafe and changing public opinion and highlighting an issue - without actually doing any scientific research. They don't need to. I remember a programme about how animals are killed for meat showing methods of killing that were quite obviously inhumane - and others which were clearly humane (apologies to vegetarians for that topic - it was an example). And likewise a documentary showing pet euthanasia and how electrocution was inhumane - and showing the fear the pet experienced just prior to the process. Coupled with a commentary explaining that and showing it visually to the viewer.
Both those programmes created a massive change in the Uk - they were broadcast on prime time television and people lobbied en-masse for law changes and achieved them.
I suppose what I'm saying is - if you show something, and highlight it, and broadcast it, you don't have to prove anything scientifically - you can just make people aware and they feel strongly enough to want to change things.
So I think scientific proof is extremely relevant in some areas - but not in others. I don't think it is right to cause suffering to an animal in the name of science. Observation and recording observations is another degree of it though.
So if wanting some scientific evidence it could be good to approach it at another angle. Rather than document the effects of hamsters in conditions which are extreme and cause them stress (eg long periods in tiny cages with no enrichment) - it could be done a different way.
So the German experiment on bar chewing and cage size (which I don't think is scientific enough as it didn't account for genetics, handling or pet ownership), observed hamsters in larger and larger cages and how bar chewing lessened the bigger and bigger the cages were. To do that, the hamster could still be in a decent sized cage for a week or two to start with - eg 60cm by 40cm.
I'm not sure it would prove anything if the hamsters were all from genetic backgrounds - because even in a very small cage, some might bar chew and some wouldn't. And presumably that's why the German research used hamsters from the same genetic background - eg bar chewer background! So they could tell at what size cage they stopped bar chewing! All that proves is that bar chewers need a certain size of cage really. Some hamsters may not bar chew but may have other, less obvious stresses. Other experiments have shown this by measuring levels of cortisol after euthanasia, from various different living conditions.
I think what is needed really is a law. And welfare organisations to agree a recommended minimum cage size plus certain requirements, specifically. They have the power to educate and broadcast things.
You may not be able to prove scientifically that a certain size cage is needed as a minimum for all hamsters, but you could broadcast that it is inhumane to keep any pet in a small cage without out of cage time or sufficient enrichment to meet their basic species-specific needs.
I don't think that is scientific - it's instinct as to what is humane and what isn't. But there still needs to be a law to stop people selling inhumane cages.
Hope that all made sense!
I can see your dilemma - you believe in scientific studies and that is important to you. I agree but not at the expense of causing suffering to prove something. Some would argue utilitarianism there (the greatest happiness for the greatest number) - saying that for some to suffer would lead to relief for millions more. And that is an argument. But personally I don't think it's right to cause suffering and there must be another way to improve conditions for the many.
Anyway what you could do is something longer term and less laboratory type research, by getting a group of people involved for a study - some who already have smaller cages with hamsters in, some who already have large cages, and make a documentary, showing what are the effects and issues people have found, showing someone being advised to upgrade and the changes it makes afterwards. Thus showing to other people the difference between a sad stressed hamster and a happy one who is able to exhibit normal behaviours.
Ultimately I think it comes down to welfare organisations. Swiss welfare is some of the strictest for hamsters I believe. They set a minimum depth of bedding of 20cm and a minimum cage size, ventilation, materials used all sorts. Yes human company and out of cage time is important too, and yes people can have their own creative choices - very large or slightly quirky cages - providing those basic needs are met.
I suppose that is why you want to approach it scientifically - to be able to persuade welfare organisations to set standards and publish and advertise those standards. Maybe enough scientific research has been done already, and what is needed is communication between welfare groups in different countries and an organisation set up (Nato for hamsters
) or United Nations for hamsters
). Type thing. A body that could then push through legislation on minimum cage size, safety of litter and required enrichment.
In the Uk there is a recent pet welfare law that puts the onus on owners to keep animals in suitable conditions. Unfortunately it's a bit vague as to what those conditions are.
But back to scientific research. Could you work with statistics rather than experiments? eg research the statistics relating to the number of hamsters who died below a certain age in certain cage sizes. Or the living conditions of certain hamsters who lived a long time?
I think one of the biggest topics is inhumane breeding practices and conditions those hamsters are kept in. Changes have been made for poultry and now they need to be made for pets (poultry is part of the food chain so it affects humans hence change more likely - much harder to get changes for pets). The RSPCA closes down such places - if they know about them.
So it would need to be - recommended cage size and enrichment for pet hamsters and recommended cage size and conditions for breeders. Plus a licence to breed required.
Anyway - I've lost myself - but if you wanted to do research scientifically - then rather than show what happens to hamster in bad conditions, maybe show the difference between average (acceptable) conditions, and very good conditions and cite other research and in depth studies, into the harm of conditions that don't provide species-speficic needs (ie enough exercise and stimulation) or unsuitable cage environment.
I believe most research cites other research to enhance an argument.
PS Going back to your initial post - you said you want to attempt to show what size of cage most hamsters thrive in. I think that is possible without keeping hamsters in poor conditions as a comparison.
One topic I'm particularly interested is further research into pain relief for hamsters and other small pets - it is inadequate, and particularly for conditions like Cushings, where the only licensed pain relief is contra-indicated. A focus more on care than on euthanasia rather than medication.