Assessing the precision of a time-sampling-based study among GPs: balancing sample size and measurement frequency

Human Resources for Health

Methodology

Lucas van der Hoek¹  Lud van der Velden¹  Daniël van Hassel²  Ronald Batenburg³  Dinny de Bakker⁴ 

[1] NIVEL, Netherlands institute for health services research, P.O. Box 1568, 3500 BN, Utrecht, The Netherlands;NIVEL, Netherlands institute for health services research, P.O. Box 1568, 3500 BN, Utrecht, The Netherlands;CAOP, P.O. Box 556, 2501 CN, Den Haag, The Netherlands;NIVEL, Netherlands institute for health services research, P.O. Box 1568, 3500 BN, Utrecht, The Netherlands;Department of Sociology, Radboud University Nijmegen, P.O. Box 9104, 6500 HE, Nijmegen, The Netherlands;null;

关键词: Time sampling;    SMS text messaging;    Confidence interval;    Sample size;    Working hours;    Health workforce planning;    General practitioners;   

DOI  :  10.1186/s12960-017-0254-8

 received in 2016-12-06, accepted in 2017-11-13,  发布年份 2017

来源: Springer

【 摘 要 】

BackgroundOur research is based on a technique for time sampling, an innovative method for measuring the working hours of Dutch general practitioners (GPs), which was deployed in an earlier study. In this study, 1051 GPs were questioned about their activities in real time by sending them one SMS text message every 3 h during 1 week. The required sample size for this study is important for health workforce planners to know if they want to apply this method to target groups who are hard to reach or if fewer resources are available. In this time-sampling method, however, standard power analyses is not sufficient for calculating the required sample size as this accounts only for sample fluctuation and not for the fluctuation of measurements taken from every participant. We investigated the impact of the number of participants and frequency of measurements per participant upon the confidence intervals (CIs) for the hours worked per week.MethodsStatistical analyses of the time-use data we obtained from GPs were performed. Ninety-five percent CIs were calculated, using equations and simulation techniques, for various different numbers of GPs included in the dataset and for various frequencies of measurements per participant.ResultsOur results showed that the one-tailed CI, including sample and measurement fluctuation, decreased from 21 until 3 h between one and 50 GPs. As a result of the formulas to calculate CIs, the increase of the precision continued and was lower with the same additional number of GPs. Likewise, the analyses showed how the number of participants required decreased if more measurements per participant were taken. For example, one measurement per 3-h time slot during the week requires 300 GPs to achieve a CI of 1 h, while one measurement per hour requires 100 GPs to obtain the same result.ConclusionsThe sample size needed for time-use research based on a time-sampling technique depends on the design and aim of the study. In this paper, we showed how the precision of the measurement of hours worked each week by GPs strongly varied according to the number of GPs included and the frequency of measurements per GP during the week measured. The best balance between both dimensions will depend upon different circumstances, such as the target group and the budget available.

【 授权许可】

CC BY   
© The Author(s). 2017