Studies on the Effectiveness of St. John's Wort for Treating Depression
Results from 26 studies on the effectiveness of Hypericum perforatum extracts (St. John's wort) for treating depression.
dat.linde2005
The data frame contains the following columns:
| id | numeric |
study number |
| study | character |
study author(s) |
| year | numeric |
publication year |
| country | character |
study location |
| ni | numeric |
total sample size |
| major | numeric |
sample restricted to patients who met criteria for major depression |
| baseline | numeric |
HRSD baseline score |
| version | numeric |
HRSD version (17 or 21 items) |
| duration | numeric |
study duration (in weeks) |
| prep | character |
Hypericum extract preparation |
| dosage | numeric |
dosage (in mg) |
| response | numeric |
definition of response (1 = HRSD score reduction of at least 50% or HRSDscore after therapy <10; 2 = HRSDreduction of at least 50%; 3 = based on HRSD scale but exact definition not reported; 4 = global patient assessment of efficacy; 5 = at least 'much improved' on the Clinical Global Impression sub-scale global improvement) |
| ai | numeric |
number of responses in treatment group |
| n1i | numeric |
number of patients in treatment group |
| ci | numeric |
number of responses in placebo group |
| n2i | numeric |
number of patients in placebo group |
| group | numeric |
stratification variable used by the authors (1 = smaller trials restricted to major depression; 2 = larger trials restricted to major depression; 3 = smaller trials not restricted to major depression; 4 = larger trials not restricted to major depression) |
The dataset includes the results from 26 double-blind placebo-controlled trials on the effectiveness of Hypericum perforatum extracts (St. John's wort) for treating depression (note that 2 studies did not provide sufficient response information).
Data were extracted from Table 1 and Figure 3. For study duration, the assessment week (instead of the total study duration) was coded for Philipp et al. (1999) and Montgomery et al. (2000). For dosage, the midpoint was coded when a range of values was given.
Linde, K., Berner, M., Egger, M., & Mulrow, C. (2005). St John's wort for depression: Meta-analysis of randomised controlled trials. British Journal of Psychiatry, 186, 99–107.
Viechtbauer, W. (2007). Accounting for heterogeneity via random-effects models and moderator analyses in meta-analysis. Zeitschrift für Psychologie / Journal of Psychology, 215, 104–121.
### copy data into 'dat' dat <- dat.linde2005 ### remove studies with no response information and study with no responses in either group dat <- dat[-c(5,6,26),] ### calculate log risk ratios and corresponding sampling variances dat <- escalc(measure="RR", ai=ai, ci=ci, n1i=n1i, n2i=n2i, data=dat) dat ### meta-analysis of the log risk ratios using a random-effects model res <- rma(yi, vi, data=dat, method="DL") res ### mixed-effects meta-regression model with stratification variable res <- rma(yi, vi, mods = ~ factor(group) - 1, data=dat, method="DL") res ### predicted average risk ratio for each level of the stratification variable predict(res, newmods=diag(4), transf=exp, digits=2)
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