One economist warns against increasing estimates for first-quarter GDP growth, because home prices keep slipping and elevated consumer spending in the fourth quarter came from savings rather than “organic income.” David Rosenberg, chief economist and strategist at Toronto-based Gluskin Sheff + Associates, said the high level of housing inventory with many cities facing backlogs between 13 and 15 months’ of supply also continues to hinder growth. “It’s a mess, and will prove to be a deadweight drag on wealth, confidence and spending,” Rosenberg said. On Friday, the Commerce Department reported fourth-quarter GDP growth of 3.2%. The Bureau of Economic Analysis said growth was fueled by a 4.4% increase in nonresidential fixed investment and stronger exports over the final three months of 2010. But Rosenberg said “it is quite possible Chinese firms rushed to catch the export rebates that ended in June,” and increased personal spending was attributable to consumers tapping savings, as organic income growth remained weak. “While the momentum heading into the first quarter is very good and it looks like Q1 GDP will be strong (a similar or better reading than Q4), we remain concerned over Q2 and believe there could be significant slowing,” Rosenberg said. A few weeks ago, Rosenberg outlined the 10 things he felt were necessary before he’d become bullish on the economic recovery, as CNBC reported. Write to Jason Philyaw.