The Patient Health Questionnaire 15 item (PHQ-15) contains the PHQ's somatic symptom scale. It is a well-validated measure, which asks whether symptoms are present and about their severity. (see: Wikipedia)
scoring_phq15(data, items = 1:15, keep = TRUE, nvalid = 12, digits = NULL)
A character vector with the PHQ-15 item names ordered from 1 to 15,
or a numeric vector indicating the column numbers of the PHQ-15 items in
Logical, whether to keep the single items and whether to return variables containing the number of non-missing items on each scale for each respondent. The default is TRUE.
A numeric value indicating the number of non-missing items required for score calculations. The default is 12.
Integer of length one: value to round to. No rounding by default.
The function returns 3 variables:
nvalid.phq15: Number of valid values (MAX=15)
score.phq15: PHQ-15 score
cutoff.phq15: PHQ-15 as categorical variable
Number of items: 15
Item range: 0 to 2
Reverse items: none
Score range: 0 to 30
Cut-off-values: < 5 = "minimal"; 5 to 9 = "mild"; 10 to 14 = "moderate"; \(\ge\) 15 = "severe"
Minimal clinically important difference: none
Treatment of missing values: Questionnaires with up to three missing values (20%) are scored,
replacing any missing values with the average score of the completed items.
Kroenke et al. 2010 (https://doi.org/10.1016/j.genhosppsych.2010.03.006)
Kocalevent et al. 2013 (https://doi.org/10.1186/1471-244X-13-91)