The average 30-year mortgage rate tracked in Freddie Mac's latest weekly survey came in slightly lower than the previous week, ending an upward week-to-week trend seen in recent surveys.Vice president and chief economist Frank Nothaft said in his weekly report that rates are still relatively low in a historical context despite the recent runup. However, he continues to expect the economy to slowly improve as he has previously forecast based on recent gains in economic indicators. He specifically cited gains in consumer spending, industrial production and exports.Gradual economic improvement could put some upward pressure on rates. At the same time Federal Reserve quantitative easing aimed at improving the economy, which officials said they could eventually adjust depending on market conditions, could be putting some downward pressure on rates. Other factors such as international financial market developments have been influencing rate behavior as well.The average primary market rate for a 30-year fixed rate mortgage during the week ending Dec. 23 was 4.81%, down from 4.83% the previous week and from a year ago when that rate was 5.05%.The average 15-year FRM rate in the latest week was 4.15%, down from the previous week's 4.17% and from 4.45% a year ago.The average rate for a five-year Treasury-indexed adjustable-rate mortgage during the week ending Dec. 23 was 3.75%, down from 3.77% the previous week and 4.4% a year ago.The average one-year Treasury ARM rate was 3.4% in the latest week, up from the previous week's 3.35% but still lower than 4.38% a year ago.Average points during the week ending Dec. 23 were 0.7 for all aforementioned loan types except the five-year Treasury hybrid, for which they averaged 0.6.