I’m not going to pretend I’m an economic wizard. I am absolutely not. But if CoL increases by 20% (random number, not real) and pay rates only increase by 1% (again, random) doesn’t your personal savings increase automatically decrease because you’re making less net income due to increased living costs?
Walking through an example...
Pants makes $100 per year
Pants COL is $80 per year
Pants saves $20 per year
= Pants' savings rate is 20%
That one should be simple to follow.
Few years later...
Pants now makes $150 per year (wages increased was 50%)
Pants DOES NOT CHANGE WHAT HE BUYS and his COL is $140 (inflation was 75%)
Pants saves $10 per year
= Pants' savings rate is 6.7%
That one should be simple to follow, too.
But then Pants decides to tighten his belt...
Makes $150
Spends $120
Saves $30
Savings rate = 20%
I think you are trying to say that declining real wages (e.g., inflation being faster than nominal pay raises) puts downward pressure on savings rates. That may be true, and I will leave the question as to if real wages have really fallen in the past 20-40 years aside for the moment. The point is, that situation does not
guarantee a lower savings rate. It still depends on how households react to those conditions. The second Pants above made 20% happen again -- he would just have to shift his consumption around a bit in order to make that happen (no more dogs).
Nothing makes you spend more (or less, for that matter). The situation you imply is that real incomes are falling over time, which, of course, makes it harder and harder to save and maintain the same level of spending, no matter what the circumstances. That might be the case, but the personal savings rate data is not somehow trying to disguise that.
The personal savings rate is not biased over time, though. It reflects the above. It is just looking at what people save versus what they spend in a given year. How and why those numbers are changing is an important conversation, but the general trend is our grandparents used to save about ~12% of their income after taxes, and it is more like ~6% now.