title: Distinguishing between frequency and intensity of health-related symptoms from diary assessments.
abstract: OBJECTIVE
  This study investigated the utility of distinguishing between the frequency and intensity of self-reported symptoms using diary-based assessments in a representative sample of U.S. residents.
  
  
  METHODS
  Data from the 2010 American Time Use Survey were analyzed, in which 12,000 respondents provided a diary about the prior day and rated their pain, tiredness, stress, and sadness for three of the day's episodes. A "two-part" latent variable modeling strategy was applied to estimate the frequency (propensity of its presence) and intensity (mean level when present) of each symptom from the diary ratings. Regression analyses comparing differences in symptom frequency and intensity across demographic factors (gender, age, income, education) were conducted to evaluate the utility of the distinction.
  
  
  RESULTS
  Frequency and intensity measures were reliably estimated from 3 daily episodes, were moderately intercorrelated for each symptom domain (rs .39 to .60), and were differentially associated with demographic factors. Gender differences were evident only in symptom intensity, not frequency, with women reporting more intense symptoms. Comparisons by age showed pronounced declines in the frequency of tiredness and stress in older age, with no age-differences in the intensity of these symptoms. Higher socioeconomic status was associated with a lower intensity of pain, tiredness, stress, and sadness, but a higher frequency of tiredness and stress.
  
  
  CONCLUSIONS
  A useful distinction between symptom frequency and intensity may be made from diary-based assessments. It reveals demographic differences that are otherwise obscured and enables a more detailed characterization of health-related experiences in people's daily life.
authors.affiliation: University of Southern California, United States. Electronic address: schneids@usc.edu.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schneider
authors.affiliation: University of Southern California, United States; Stony Brook University, United States.
authors.forename: Arthur A
authors.initials: AA
authors.lastname: Stone
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D005221:Fatigue / Q000453:epidemiology*; D005260:Female; D006304:Health Status; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010146:Pain / Q000175:diagnosis / Q000453:epidemiology*; D010147:Pain Measurement; D015203:Reproducibility of Results; D012107:Research Design; D012494:Sampling Studies; D057566:Self Report; D012720:Severity of Illness Index; D012737:Sex Factors; D013315:Stress, Psychological / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology
keywords: Diary; Frequency; Intensity; Pain; Sadness; Stress; Tiredness; Two-part model