> […] they changed it to make the numbers look better.

They changed the number because the number was not modelling reality as accurately as it could have.

Perhaps actually read the Boskin Report:

> 5. Changes in the CPI have substantially overstated the actual rate of price inflation, by about 1.3 percentage points per annum prior to 1996 (the extra 0.2 percentage point is due to a problem called formula bias inadvertently introduced in 1978 and fixed this year). It is likely that a large bias also occurred looking back over at least the last couple of decades.

> 6. The upward bias creates in the federal budget an annual automatic real increase in indexed benefits and a real tax cut. CBO estimates that if the change in the CPI overstated the change in the cost of living by an average of 1.1 percentage points per year over the next decade, this bias would contribute about $148 billion to the deficit in 2006 and $691 billion to the national debt by then. The bias alone would be the fourth largest federal program, after social security, health care and defense. By 2008, these totals reach $202 billion and $1.07 trillion, respectively.

> 7. Some have suggested that different groups in the population are likely to experience faster or slower growth in their cost of living than recorded by changes in the CPI. We find no compelling evidence of this to date (in fact just the opposite) but further exploration of this issue is desirable.

* https://www.ssa.gov/history/reports/boskinrpt.html

* https://en.wikipedia.org/wiki/Boskin_Commission

Feel free to point out any errors in the methodology and logic that they used.

Here's a paper from 2006 to get you started:

> This paper provides a retrospective on the 1996 Boskin Commission Report, Toward a More Accurate Measure of the Cost of Living, and its famous estimate that the CPI in 1995-96 was upward biased by 1.1 percent per year. The paper summarizes the report's methods, findings, and recommendations, and then reviews the criticisms that appeared soon after the Report was issued. Post-Boskin changes in the CPI are summarized and assessed, as is recent research on related issues. The paper sharply distinguishes two questions. First, with what we know now, what should the Commission have concluded about CPI bias in 1995-96? Second, what is the bias now after the many improvements introduced into the CPI since the Commission's Report?

> About the first question, my own recent research on apparel and rental housing indicates a substantial downward bias in the CPI over much of the twentieth century, diminishing in size after 1985. Incorporating these findings into the Boskin matrix would reduce its 0.6 percent annual upward bias due to quality change and new products to a smaller 0.4 percent bias. However, this is more than offset by the stunning discrepancy over 2000-06 in the chain-weighted C-CPI-U compared to the traditional CPI-U, indicating that the Commission greatly understated the magnitude of upper-level substitution bias. This retrospective evaluation suggests that the Boskin bias estimate for 1995-96 should have been 1.2 to 1.3 percent, not 1.1 percent.

> Current upward bias in the CPI is estimated to have declined from the revised 1.2-1.3 percent in the Boskin era to about 0.8 percent today. Yet the Boskin report, like most contemporary studies of quality change, failed to place sufficient value on the value of new products and on increased longevity. Allowing for these, today's bias is at least 1.0 percent per year or perhaps even higher.

* https://www.nber.org/papers/w12311