ALBANY (New York) - STUDENTS who rely on working at night to improve their grades might want to sleep on that strategy: a new survey in the US says those who never study all night have slightly higher grades than those who do.

A survey of 120 students at St Lawrence University, a small liberal arts college in northern New York, found that students who have never pulled an all-nighter have higher grades than those that have not.

The survey found those who never worked all night had a 3.1 grade point average, with 4 being the highest on the scale, compared with 2.9 for those who have.

The study, by assistant professor of psychology Pamela Thacher, is to be included in the January issue of Behavioral Sleep Medicine.

'It's not a big difference, but it's pretty striking,' she said. 'I am primarily a sleep researcher and I know nobody thinks clearly at 4 in the morning. You think you do, but you can't.'

A second study by Ms Thacher, a clinical psychologist, had 'extremely similar' results showing lower grades among the sleep skippers.

Many college students, of course, have inadequate or irregular sleep, for reasons ranging from excessive caffeine to poor time management.

Prav Chatani, a St Lawrence sophomore who wasn't involved in either study, said the findings made sense.

The neuroscience major has been pulling fewer all-nighters, but recently stayed up until 'around 4 or 5 in the morning' to prepare for an organic chemistry test and a neuroscience presentation, he said.

He found himself unable to remember some of the things he had studied.

'A lot of students were under the impression all-nighters were a very useful tool for accomplishing work, that caffeine intake was very useful in meeting deadlines and stuff like that,' said Mr Chatani, who had a 3.4 grade point average, or GPA, last semester and doesn't expect to do too badly this semester, either.

Dr Howard Weiss, a physician at St Peter's Sleep Center in Albany, said the study results make sense.

'Certainly that data is out there showing that short sleep duration absolutely interferes with concentration, interferes with performance on objective testing,' he said.

Some night owls do get good grades, of course, which may be explained by circadian rhythms, Weiss said. Circadian rhythms can be tracked through body temperature and hormonal transmissions.

Some people have different 24-hour body clocks than others, and may do better depending on class and testing times, Dr Weiss said.

Chloe LaFrance, a St Lawrence junior from Elizabethtown majoring in psychology and English, said she's never studied all night. 'If I get less than six hours of sleep I just do not function at all,' she said.

Ms LaFrance, who has about a 3.7 GPA, said she's never had a situation where she couldn't get all her work done.

'I'm in a crunch period right now,' she said. 'I just find I work better when I get sleep. I'm actually more productive.'

In Ms Thacher's first study, 65 students said they had pulled one or more all-nighters, and 45 said they hadn't done any.

The survey was conducted in Psychology 101 classes, and included students in a variety of majors. -- AP