Wednesday, October 29, 2008


Psychometricians go to great lengths to maximize the reliability of the self-reports that they use but most medical researchers don't even seem to know that there is a problem there. The revelation below that actual behaviour and self reported behaviour share only 22% of their variance (r=.47) should ring warning bells but it won't

Self-Reported and Measured Sleep Duration: How Similar Are They?

By Lauderdale, Diane S. et al.


Background: Recent epidemiologic studies have found that self-reported duration of sleep is associated with obesity, diabetes, hypertension, and mortality. The extent to which self reports of sleep duration are similar to objective measures and whether individual characteristics influence the degree of similarity are not known.

Methods: Eligible participants at the Chicago site of the Coronary Artery Risk Development in Young Adults Study were invited to participate in a 2003-2005 ancillary sleep study; 82% (n = 669) agreed. Sleep measurements collected in 2 waves included 3 days each of wrist actigraphy, a sleep log, and questions about usual sleep duration. We estimate the average difference and correlation between subjectively and objectively measured sleep by using errors-in-variables regression models.

Results: Average measured sleep was 6 hours, whereas the average from subjective reports was 6.8 hours. Subjective reports increased on average by 34 minutes for each additional hour of measured sleep. Overall, the correlation between reported and measured sleep duration was 0.47. Our model suggests that persons sleeping 5 hours over-reported their sleep duration by 1.2 hours, and those sleeping 7 hours over-reported by 0.4 hours. The correlations and average differences between self-reports and measured sleep varied by health, sociodemographic, and sleep characteristics.

Conclusion: In a population-based sample of middle-aged adults, subjective reports of habitual sleep are moderately correlated with actigraph-measured sleep, but are biased by systematic over-reporting. The true associations between sleep duration and health may differ from previously reported associations between self-reported sleep and health.

Epidemiology. 19(6):838-845, November 2008

Breast scans of no use to young women, says doctor

Good to see this message getting out. There is some reason to believe that ALL routine breast examinations are pointless and may even be counterproductive. See e.g. here

The deaths of Jane McGrath and Belinda Emmett from breast cancer are driving large numbers of young women to have mammograms which may be of no use. Experts have warned the scans bring no benefit for females under 40.

The so-called "Kylie effect" remains around the disease, with overblown public perception of rising rates of breast cancer in younger women and confusion around the best ways to detect it. "It is important to dispel the misconceptions, address unnecessary alarm and provide the facts for this age group," Dr Helen Zorbas, director of the National Breast and Ovarian Cancer Centre, said at the launch of breast cancer awareness day in Sydney. She said women under 40 made up just 6 per cent of the 12,000 females diagnosed with the disease, and rates remained static. However, younger women are more prone to an aggressive form of the disease and have a 39 per cent increased risk of dying.

Diagnoses among young celebrities like pop star Kylie Minogue, fashion designer Heidi Middleton and actress Christina Applegate, and the deaths of Jane McGrath, wife of former Australian cricketer Glenn McGrath, and actress and singer Belinda Emmett, have given the public the misguided impression of an epidemic among the young, she said. "The so-called 'Kylie effect' led to an increase in the number of women who made bookings for mammograms but many of these women were in the under 40 age group, where mammographic screening is not effective," Dr Zorbas said.

Her audience at the launch included Prime Minister Kevin Rudd, federal Opposition Leader Malcolm Turnbull and a host of other dignitaries, doctors, scientists and survivors. Screening programs have reduced breast cancer deaths by 30 per cent among women aged 50-69 years, because the small white abnormalities can be detected with relative ease. Younger, denser breasts, however, resemble "cotton wool" in scans, making the lumps unrecognisable. "Early detection for breast cancer in young women relies almost completely on young women themselves, knowing their own bodies and picking up the early signs of the disease," Dr Zorbas said.

A new campaign recommends "breast awareness" for young women, encouraging them to check themselves regularly for lumps using no special technique after international studies found specific checking styles didn't reduce cancer deaths. The retro-style advertisements encourage women to check their breasts as part of everyday life, while drying their hair or waiting for the toast to pop. Studies show women can also reduce their breast cancer risk by up to 30 per cent by keeping alcohol consumption to a minimum, exercising regularly and maintaining a healthy body weight.

Mr Rudd told the audience Australia needed to do better in tackling all forms of cancer. "It's time as a nation that we renew our national efforts in what must be a national war against cancer," he said.


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