Long term studies tell us mainly about the middle class

The authors below put a brave face on their findings, saying that "qualitative" findings persist but numbers are the stuff of science and they change the longer the study lasts  -- with mostly middle class patients staying in lengthy studies. 

That pesky social class again!  It is second only to age for wide-ranging health effects yet is more often than not ignored in medical research.  So it is refreshing to see one study that does look at it  -- albeit that the findings are unsurprising.

Loss to Follow-up in Cohort Studies: Bias in Estimates of Socioeconomic Inequalities

By Howe, Laura D. et al.

Abstract

Background: Although cohort members tend to be healthy and affluent compared with the whole population, some studies indicate this does not bias certain exposure-outcome associations. It is less clear whether this holds when socioeconomic position (SEP) is the exposure of interest.

Methods: As an illustrative example, we use data from the Avon Longitudinal Study of Parents and Children. We calculate estimates of maternal education inequalities in outcomes for which data are available on almost the whole cohort (birth weight and length, breastfeeding, preterm birth, maternal obesity, smoking during pregnancy, educational attainment). These are calculated for the full cohort (n~12,000) and in restricted subsamples defined by continued participation at age 10 years (n∼7,000) and age 15 years (n∼5,000).

Results: Loss to follow-up was related both to SEP and outcomes. For each outcome, loss to follow-up was associated with underestimation of inequality, which increased as participation rates decreased (eg, mean birth-weight difference between highest and lowest SEP was 116 g [95% confidence interval = 78 to 153] in the full sample and 93 g [45 to 141] and 62 g [5 to 119] in those attending at ages 10 and 15 years, respectively).

Conclusions: Considerable attrition from cohort studies may result in biased estimates of socioeconomic inequalities, and the degree of bias may worsen as participation rates decrease. However, even with considerable attrition (>50%), qualitative conclusions about the direction and approximate magnitude of inequalities did not change among most of our examples. The appropriate analysis approaches to alleviate bias depend on the missingness mechanism.

Epidemiology: January 2013 - Volume 24 - Issue 1 - p 1–9

Statins have helped slash British heart attack deaths, "Experts say"

This is just faith.  There is no way of separating out statin effects from other effects mentioned below.  Wider use of aspirin  and other clotbusting drugs could be major factors, for instance

Statins have played a significant role in slashing the number of deaths from heart attacks by half.  The 'wonderdrug' can reduce cholesterol and protect against a host of chronic illnesses.

Experts have said the drug has contributed to the saving of millions of lives over the past ten years.

Between 2002 and 2010 the death rate in men fell dramatically from 78.7 per 100,000 to 39.2, figures show.  In comparison, the death rate among women fell from 37.3 to 17.7, according to the British Heart Foundation.

Professor Peter Weissburg, medical director of the foundation, told the Daily Express: 'Around 50 per cent fewer people are having heart attacks in the first place and statins play a big part on primary and secondary intervention.  'Until statins came along we didn't have drugs that were effective and safe.'

Every day eight million people in the UK take various statins, which cost as little as 40p a day.

Simvastatin is the most frequently prescribed one; last year GPs gave out almost three million prescriptions for it in England alone.

Their widespread use, combined with healthier lifestyles, has led to far fewer people having heart attacks.

Mr Weissburg added: 'The fall in the number of deaths from heart attacks has actually been dropping for the past 20 years and some of that is to do with lifestyle'.

Mr Weissburg said fewer people smoking, better control of blood pressure and better treatment for those who have suffered a heart attack, as well as statins, have contributed to the fall.

The success of statins in combating fatal heart attacks has led to some doctors calling for everyone over 50 to be prescribed the pills.

They protect against heart attacks, heart disease and strokes, as well as some cancers.

In November it was reported that thousands of people taking a common statin were to have their dose reduced over fears of side effects.

Side effects can include insomnia, bowel problems, headaches and loss of sensation or pain in the hands and feet.

The medicines regulator warned that patients taking one particular type - simvastatin - at the same time as other drugs used to reduce high blood pressure were likely to suffer more muscle aches and pains.

SOURCE