This may seem a little on the weird side....but I had this on my mind and had to share....My cousin in law, a police officer, was injured when he was hit by a car back in July. He has since been released and is recovering well, but still has a ways to go. While he was in the hospital, I was helping renovate the bathroom (and other things) at his house to make it more wheelchair friendly. When the bathroom was redone, I noticed that the bathtub is fixed where you climb in/out on the left hand side....This made me think...Isn't that the wrong way of sorts? However, I remember the house is an older house and so maybe that's the way the bathtub was in the beginning. I began to think back, and every house that I have lived in, and for that matter almost all of my relatives and friends houses had right side bathtubs. Both of my bathtubs at my house are right siders, but I have an aunt whose house was built around 1988 where both bathtubs were upstairs and left siders, and another aunt from out of town whose bathtub was upstairs and a left sider, but that's the only other times I remember a left side bathtub. Just curious, are your bathtubs left siders or right siders (the side that you climb out on). Thanks for reading and sharing!
I have one of each. Master bath is a left. Upstairs is a right.
Both tubs are perpendicular to exterior walls, so their plumbing runs in the interior walls.
Have a friend who is a plumber. He installed his bath tub with shower heads on BOTH sides. Control knobs on BOTH sides, so that he AND his wife could shower together and each have their own style of shower head and temperature of water as desired. I thought it novel.
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Hmmmm... never gave it much thought but I recall almost every one I have seen is a left sider except an ad-hoc one my uncle set up that was right sided.
I like the idea of the two shower heads mrzed describes... I guess when you're a plumber you can "afford" to be "ambidextrous"!
My downstairs bath (the original to the house) is a lefty, as is my Grandmother's. Both are pre WW2. Both in my parent's house are right side. Never had thought about that.
We have right sided bath tubs.
WARHAWK
One of my bathrooms is a lefty and the other one is ADA approved to accommodate my wheelchair.
I have both kinds in the houses I've lived in over the years.
I guess it depends on which way you're facing when you get in Harry, lol.
I guess it depends on which way you're facing when you get in Harry, lol. 
I've been assuming left and right refer to facing the showerhead / valve assembly.
When I say left side or right side, it's referring to the side where the shower curtain (if any) would hang. Which side do you step out on when facing the faucet/showerhead?