By CELESTE BOTT
LANSING – Retail sales have yo-yoed in recent months, including a dip in December, but Michigan businesses say their overall holiday sales improved from 2011. But the challenge now is overcoming a significant sales decline at the end of the year. Fifty-four percent of retailers reported better holiday sales than in 2011, while 30 percent reported declines. The Michigan Retail Index, a joint project of the Michigan Retailers Association and the Federal Reserve Bank of Chicago, measures the performance of the state’s retail industry. Data is based on the Federal Reserve and the association’s monthly membership surveys.