Precision of rate estimation under uniform interval censoring.

Medical events are often recorded not at their time of occurrence but rather at a subsequent examination. In survival analysis, this is called interval censoring. This paper presents a relationship between the sampling error of the estimated event rate and the number of examinations, which are assumed to be evenly spaced throughout the study. This relationship should help balance the cost of additional examination rounds against the precision gained

Residuals for proportional hazards models with interval-censored survival data

We develop diagnostic tools for use with proportional hazards models for interval-censored survival data. We propose counterparts t o the Cox-Snell, Lagakos (or martingale), deviance, and Schoenfeld residuals. Many of the properties of these residuals carry over to the interval-censored case. In particular, the interval-censored versions of the Lagakos and Schoenfeld residuals may be derived as components of suitable score statistics. The Lagakos residuals may be used to check regression relationships, while the Schoenfeld residuals can help to detect nonproportional hazards in semiparametric models. The methods apply to parametric models and to the semiparametric model with discrete observation times

Postal survey methodology to assess patient satisfaction in a suburban emergency medical services system: an observational study

Abstract Background Patient satisfaction is of growing importance to providers of emergency medical services (EMS). Prior reports of patient satisfaction have frequently used resource-intensive telephone follow-up to assess satisfaction. We determine the feasibility of using a single mailing, anonymous postal survey methodology for collecting patient satisfaction data from a suburban EMS system. Methods Patients transported between January 2001 and December 2004 were mailed a brief satisfaction questionnaire. The questionnaire was printed on a pre-addressed, postage paid postcard and consisted of five questions that used a five-point Likert scale to assess satisfaction with EMS personnel and services provided. Three open-ended questions assessed concerns, the most important service provided, and methods for improving service. Survey response rate was the primary outcome of interest. The Chi-square test was used to compare rates between years. Results The survey required about 6 man hours and cost about $70 per month. Overall response rate was 32.0% (857/2764; 95CI 30.3% – 33.9%). During the first year, response rate was 42.6% (95CI 38.5% – 46.8%), but was significantly lower in subsequent years (29.0% in year 2, 30.8% in year 3, and 27.6% in year 4, p Conclusion Postal surveys for assessing patient satisfaction following EMS transport can achieve comparable response rates to similar surveys in other health care settings. Response rates did not decline after the second year of patient surveys, suggesting some stability after the initial year. Interpersonal communication was determined to be the single most important contributor to patient satisfaction.</p