That article isn't too convincing since they claim that most of the reason for Texas having a higher effective rate for lower income is sales and excise tax - but the sales tax is 9% in California and 6.25% in TX (~8% with local taxes), not to mention gasoline taxes, etc.

Property taxes are higher, but housing prices are lower in TX than CA. From what I've seen they are a bit of a wash (tax rate is double, but housing prices are 50% or less).

And in the methodology section it says "The report also includes the effect of indirect consumption taxes: the sales and excise taxes that are paid initially by businesses rather than individuals". So it looks like they assumed those taxes are passed through to consumers when in fact they aren't, at least not 100%.

They also exclude all tax payers over 65.