First rule of reading scientific papers: just look at the plots, the rest is usually irrelevant. This plot from the paper shows how much patients improved when they were given either an antidepressive drug or a placebo.
Maybe there are too many dots and curvy lines to see what is happening. After squinting my eyes a bit, I have, using the power of MS Paint, reproduced the main features of this plot.
Note the baseline, which the authors felt was unnecessary. Mistake. First rule of drawing plots: add a baseline. Looking at the plot, and looking at the baseline, I drew the following conclusions:
1/ Taking antidepressive drugs improves, on average, the mood of people with all degrees of depression. Woohoo.
2/ For people with mild depression, the same improvement can be made with a placebo. For these people, it is not the active chemical of the antidepressive that is helping them, but the circumstances of being given and taking a "cure". This could lead to a long debate about the ethics and effectiveness of giving patients a placebo cure.
3/ For people with severe depression, the chemicals of the antidepressive work and improve their mood. Woohoo.
So antidepressive drugs have been shown to improve the mood of people with severe depression above the level achieved by a Placebo. Or, as summarised in the Guardian:
Prozac, the bestselling antidepressant taken by 40 million people worldwide, does not work and nor do similar drugs in the same class, according to a major review released today.
This is obviously bullshit, as a second look at those graphs will tell you. More subtle is the mistake made by the authors, who conclude:
The relationship between initial severity and antidepressant efficacy is attributable to decreased responsiveness to placebo among very severely depressed patients, rather than to increased responsiveness to medication.
This is confused thinking. Taking any drug gives potentially a medication effect and a placebo effect. If the total improvement caused by taking the drug stays the same, but the placebo effect diminishes, then the response to medication effect must have increased: the drug works.
Maybe there are other, better, options for some people, but antidepressive drugs do on average have a positive effect for people with severe depression.
This blog discusses the difference between statistical and clinical significance (the funny green area in the plot), so that I don't have to.
Don Jewett is an emeritus Prof. at the University of California and knows how to use his CAPSLOCK. He takes issue with the conclusions of the paper (link added 28. Feb)
The language log get into the graph-drawing spirit. I like their old-skool noughts and crosses marker styles. They also summarise the press coverage.(link added 1. Mar)