Monitoring the quality of the trial is essential to ensure a robust study and maintain internal validity. Several procedures were employed to optimize the quality of the study and maximize validity and reliability of the program delivery and outcome assessments. These are described below.
In order to ensure accurate and consistent measurements, the study weight scale was professionally calibrated once a year and the height scale checked and recalibrated daily before measurements commenced.
Questionnaires to obtain current medical conditions and medications and were completed by participants at each data collection session. Smoking status and postcode as a proxy for socio-economic status were collected once.
Laboratory-based assessments took place in the Human Performance Laboratory at the University of Newcastle, Callaghan campus. Assessments occurred at baseline, 3, 6 and 18 months and an extra 9 months assessment for the control participants.
Height: measured to 0.1 cm using the stretch stature method on a Harpenden portable stadiometer (Holtain Limited, Dyfed, Britain). Height was measured twice, with accepted values within 0.3 cm. A third measure was taken if measurements were outside the acceptable range. The average of the two acceptable measures will be reported.
Weight: measured in light clothing, without shoes on a digital scale to 0.01 kg (CH-150kp, A&D Mercury Pty Ltd, Australia). Weight was measured twice, with accepted values within 0.1 kg. A third measure was taken if measurements were outside the acceptable range. The average of the two acceptable measures will be reported.
Waist circumference: measured to 0.1 cm using a non-extensible steel tape (KDSF10-02, KDS Corporation, Osaka, Japan). Waist circumference was measured at two points (i) level with the umbilicus and (ii) at the narrowest point between the lower costal border and the umbilicus. Two measures were taken at each site, with accepted values within 0.5 cm. Further measures were taken if measurements were outside the acceptable range. The average of the two acceptable measures will be reported.
Body mass index (BMI): calculated from height and weight (kg/m2).
Dietary intake is assessed using the Australian Eating Survey (AES). AES is a 120-item semi-quantitative FFQ, used previously in Australian youth up to 16 years  and currently being validated in both adult males and females. Portion sizes for individual food items were generated by the Australian Bureau of Statistics (ABS)  and unpublished data from the 1995 Australian National Nutrition Survey; or the "natural" serving size for common items such as a slice of bread. Subjects were asked about frequency of their consumption over the previous six months with frequency options ranging from 'Never' up to '4 or more times per day' but varying depending on the food item. Twenty-one questions related directly to the intake of vegetables and 11 questions related to fruit. Seasonal availability of some fruits will be considered in the nutrient analysis.
Nutrient intakes from the FFQ were computed from the most current food composition database of Australian foods available, the Australian AusNut 1999 database (All Foods) Revision 17 and AusFoods (Brands) Revision 5 (Australian Government Publishing Service, Canberra) to generate individual mean daily macro-and micro-nutrient intakes.
The AES includes questions about the total number of daily serves of fruit, vegetables, bread, dairy products, eggs, fat spreads, sweetened beverages and snack foods, as well as asking the type of bread, dairy products and fat spreads used. Twelve questions relate to food-related behaviours, including items on frequency of take-away food consumption and eating while watching television.
The Three Factor Eating Questionnaire-R18, (TFEQ-R18) is a self-assessment questionnaire to measure cognitive and behavioural components of eating in obese populations across three scales of cognitive restraint, uncontrolled eating and emotional eating . The 18 items are coded on a four-point scale with higher values indicating the behaviour is expressed more frequently or the statement is more correct for the participant.
International Physical Activity Questionnaire (short form): data from this questionnaire was used to estimate total MET-minutes/week and to classify participants into either high, medium or low physical activity categories according to the IPAQ Scoring Protocol .
Pedometers: physical activity was objectively measured using pedometers (Yamax SW700; Yamax Corporation, Kumamoto City, Japan). At baseline, participants were instructed on how to attach the pedometers (at the waist on the right hand side) and asked to remove the pedometers only when sleeping, when the pedometer might get wet (e.g. swimming, showering) or during contact sports. Participants were asked to wear pedometers for seven consecutive days and keep to their normal routine. At the end of the day participants were instructed to record their steps on a pedometer record sheet and reset their pedometers to zero. Participants were instructed to record if they did an activity like cycling, swimming, contact sports or another activity that did not involve stepping and include details (type of activity and duration), or if they forgot to wear their pedometer for an amount of time. Participants will be included in all analyses if they completed at least four weekdays of pedometer monitoring. The average of existing days will be imputed for participants who have included at least four days of data.
Online diet and physical activity diary
The Australian Biggest Loser Club online food and exercise diary is powered by the database (International Food and Exercise Database). This database holds the information on over 70,000 foods including 20,000 Australian foods, 250,000 food portions, 5000 meals and recipes, and 1000 exercises. It is derived from a combination of methods including: 1) nutrition information from branded products collected by SP Health; 2) recipes to derive commonly eaten foods developed by an Accredited Practising Dietitian; and 3) sources such as the Australian food database (NUTTAB 2006, Canberra). The METs of exercises have been obtained predominantly from the Ainsworth [19, 20] compendium of activities, and all exercise instructions have been compiled by SP Health.
Indicators of change in Health Status and Quality of Life
Blood pressure and resting heart rate: systolic blood pressure, diastolic blood pressure and heart rate were measured using an automated blood pressure monitor (NISSEI/DS-105E digital electronic blood pressure monitor (Nihon Seimitsu Sokki Co. Ltd., Gunma, Japan) under standardized conditions. Subjects were seated for five minutes before the first blood pressure measurement and a rest period of two minutes between measures. Blood pressure was measured three times. Further measurements were taken if the blood pressure or resting heart rate values fell outside of the acceptable ranges i.e. systolic within 10 mmHg, diastolic within 10 mmHg (preferably 5 mmHg) and resting heart rate within 5 bpm. The mean of the two closest systolic pressures and the diastolic pressure paired to them will be reported. The mean of the two lowest resting pulse pressures will be used.
Blood sample biomarkers: blood samples were collected after an overnight fast and analysed using standard automated techniques at a single National Association of Testing Authorities accredited pathology service. The samples were analysed for lipids (Total Cholesterol, Low Density Lipoprotein (LDL) and High Density Lipoprotein (HDL) cholesterol, and triglycerides), thyroid function and liver function, C-reactive protein, glucose and insulin. Additional samples have been stored for future analysis of additional biomarkers.
Quality of Life: SF-36, version 2.0 (QualityMetric Incorporated, Lincoln, RI, USA) is a multi-purpose, generic short-form health survey consisting of 36 questions using an 8-scale profile of functional health and well-being scores and psychometrically-based physical and mental health summary measures and scored according to standardised procedures . It has been used widely in surveys of general populations and in differentiating the health benefits produced by a range of different treatments.
Use of Internet features and satisfaction with weight loss program
A process evaluation questionnaire was developed from a previous study  to assess the use of website features and satisfaction with the web based program, and completed by participants after 3, 6 and 18-months. Objective measurement of participants' use of the website features (e.g. log-ins to specific program features, diary entries, post to bulletin boards) was collected and stored by SP Health Pty Ltd throughout Phase 1 and Phase 2.
Timelines for Programs
Baseline assessments occurred in one session and participants in the two intervention groups were able to log on and commence the programs immediately after this initial assessment. This session was conducted early in the morning and participants were offered breakfast following the blood collection, anthropometric and blood pressure assessments. Participants repeated these assessments at 3, 6, and 18 months with the control group having their post-intervention assessments at 9 and 21 months (due to their 3 months wait-list period). To maximize adherence to these sessions, participants were asked to book into an assessment time that suits them using the online scheduling system, Doodle http://doodle.com or alternatively via a telephone call. In addition, for participants difficult to contact other methods were employed such as text messaging and mailing letters. A contribution towards parking and travel costs of $AU10 was given to those attending assessment sessions.