Research Design

The SHAHRP Study Research Design and Methodology

The SHAHRP study focuses on the development and implementation of a classroom-based alcohol education program.

The SHAHRP study is a harm minimisation study. It combines an evidence-based harm minimisation intervention with longitudinal measures of alcohol-related harm to assess change in the study students alcohol-related experiences. The critical evidence-based features of the SHAHRP intervention were drawn from a range of health and drug education program and research literature, and in particular, published evaluation studies and research that demonstrated some potential for behaviour change in the target population.

Methods

Research

Design: SHAHRP is an efficacy study based on a quasi-experimental, intervention research design. The study explores the effects of a student focused, secondary school, alcohol curriculum program on students’ alcohol related knowledge, attitudes, patterns and context of alcohol use and alcohol related harm. The study reflects the Australian National Drug Strategy by adopting a harm minimisation approach, in this case, aiming to reduce the level of alcohol related harm in students who drink alcohol, and to reduce the harm experienced by those students who do not drink alcohol, but socialise with others who do drink. Figure 1 provides an overview of the study design including phases of intervention and data collection.

Figure 1: Overview of Study Design

Month and year	2/97	5/97 8/97	10/97	5/98	10/98	10/99	10/00	10/01
Intervention group	O1	X1	O2	X2	O3	O4	O5	O6
Control group	O1		O2	X	O3	O4	O5	O6

Key:	X: Intervention	X control school regular alcohol education
	O: Observation

Sampling: The study sample was selected using cluster sampling, with stratification by socio-economic area. The baseline sample size of 2300 students takes into account the design effect created by cluster sampling. The fourteen schools involved in the SHAHRP study represent approximately 23% of government, secondary schools in the Perth metropolitan area. These schools were also selected to incorporated feeder schools for the Western Australian School Health Project. Random allocation to intervention and control conditions occurred by school, however, this resulted in differential acceptance. One school targeted for the intervention preferred to participate as a control school. This differential acceptance therefore influenced the allocation of some students to treatment and control conditions. A sensitivity analysis indicated that there was no difference in the overall results when this school was excluded from the analysis.

Power calculations suggest that a minimum of 800 subjects were required to achieve statistical power greater than 0.9 to detect an effect size of 0.15 with a coefficient variation of 25% through simple random sampling. The SHAHRP sample of 2343 cases (intervention students n=1111, control group students n=1232) take into account the design effect created by cluster sampling (design effect = 1.48; minimum sample required = 1184) and allows scope for an expected attrition rate of fifteen percent per year.

Retention: The retention rate was 75.9% over 32 months.

The questionnaire: The SHAHRP survey instrument was purposely developed and tested to measure students' knowledge, attitudes, patterns of use, context of use, harm associated with the students own use of alcohol and harm associated with other people’s use of alcohol. The conceptual basis of the measures included in the SHAHRP survey draws on several studies, interventions and student generated data. In addition, several measures of harm were identified and defined by students during focus groups conducted in the formative year of SHAHRP. Extensive pre-testing of the SHAHRP questionnaire was undertaken during the formative period of the study. Validity measures included the assessment of face and content validity, using expert review, target group review and statistical review of the survey. Internal consistency and the test-retest procedures were used to determine the reliability of the SHAHRP survey. The test-retest was conducted with four classes of year nine students (approx. 120, 14 year old students) from the pilot schools. These students completed the survey on two occasions, separated by two weeks. If the test-retest analysis indicated that an individual item was likely to be unreliable then that item was excluded from the analysis and was not reported in the results. However, these items are maintained as scale or index items as face validity, content validity and internal consistency would be compromised with their exclusion. The anonymous, self completion surveys were completed by study students under the guidance of trained researchers who instructed students and responded to questions following a set procedure. In addition, the survey protocol involved providing a verbal summary of the study and its design to both intervention and control students and teachers. In line with local Education Department policy classroom teachers were in attendance, however, they were requested to refrain from moving about the room to limit any possible influence on students responses.

Data analysis: Four scales/indices were developed to assess overall change. These were: knowledge index (19 items; internal consistency: 0.73); attitude scale (six items; internal consistency: 0.64); harm associated with own use of alcohol index (17 items; internal consistency: 0.9); harm associated with others’ use of alcohol index (six items; internal consistency: 0.70). The knowledge index represents actual number of correct answers to knowledge questions; the attitude scale was a sum of the six attitude variables with lower scores representing safer alcohol related attitudes; and the harm indices measure number of harms experienced. Consumption was measured using two variables related to how often alcohol was consumed and how much alcohol was consumed per occasion. Risky drinking was also assessed. Context of use was measured using six variables related to situation of use to define non-drinkers, supervised drinkers and unsupervised drinkers. Multi level modelling procedures were used to analyse the results of the study.

For more information about the research methodology contact Senior Investigator:
Nyanda McBride: n.mcbride@curtin.edu.au
or NDRI secretary: ndri@curtin.edu.au

Phone: +61 8 9266 1600 (main)
Fax: +61 8 9266 1611
National Drug Research Institute
Curtin University
GPO Box U1987
Perth WA 6845 Australia