Despite the well-documented health benefits, large numbers of children in Australia( Reference Magarey, Daniels and Smith 1 , 2 ) and elsewhere( Reference Fox, Pac and Devaney 3 , Reference Muñoz, Krebs-Smith and Ballard-Barbash 4 ) consume diets inconsistent with the recommendations of health organisations. Of particular concern are discrepancies between recommended intakes and children’s actual intakes of fruits and vegetables, water, sugar-sweetened beverages, food variety and non-core (i.e. energy-dense, nutritionally poor) foods( Reference Rangan, Randall and Hector 5 ). In order to shift children’s food intakes closer to dietary recommendations, a good understanding of the factors affecting children’s food intakes is needed( Reference Steptoe, Pollard and Wardle 6 ).
While there is a range of individual and environmental influences on children’s food intakes, food preferences have consistently been shown to be particularly influential. Existing patterns of food preferences tend to impede the consumption of a healthy diet by hindering the consumption of healthy foods and promoting the consumption of non-core foods, especially in children( Reference Birch, McPhee and Bryant 7 – Reference Bere and Klepp 10 ). That is, children prefer foods that are recommended to be consumed infrequently or in small amounts (non-core foods) while the most disliked foods include those that promote good health, notably vegetables( Reference Russell and Worsley 11 – Reference Zeinstra, Koelen and Kok 14 ). Children are thought to be in a sensitive period for learning about food between the ages of 2 and 5 years, when they are particularly receptive to learning about food acceptability( Reference Cashdan 15 ). During this period children appear to develop dislikes for many foods, especially vegetables( Reference Skinner, Carruth and Wendy 12 ). These developed likes may translate into food patterns that influence food choice during childhood and adulthood( Reference Skinner, Carruth and Wendy 12 , Reference Birch and Marlin 16 – Reference Unusan 18 ). For this reason, identification of factors that influence children’s food preferences within this age group will help in the effective design of interventions to improve children’s food preferences and dietary intakes.
Children develop their food preferences largely through repeated exposure to foods( Reference Nicklaus, Boggio and Chabanet 17 , Reference Lakkakula, Geaghan and Zanovec 19 – Reference Wardle, Herrera and Cooke 23 ). Parents are arguably the most important environmental variable affecting the development of children’s food preferences due to their role in determining which foods children are exposed to( Reference Peters, Sinn and Campbell 24 ). Indeed parents, and the wider community, see parents, especially mothers, as influential and responsible for children’s food preferences and dietary intakes( Reference Skinner, Carruth and Wendy 12 , Reference Stratton and Bromley 25 , Reference Hart, Herriot and Bishop 26 ). Intervention studies aimed at modifying children’s food preferences, weight status and dietary intake support these lay views of the importance of parents: those interventions in which parents were involved tended to have more positive effects on dietary behaviour change than interventions that did not incorporate parents( Reference Bourcier, Bowen and Meischke 27 ). Furthermore, parents are the primary agents of socialisation for children of pre-school age( Reference Parke and Buriel 28 ). Despite the significant role of parent-led exposure in determining children’s food preferences( Reference Wardle, Cooke and Gibson 22 ) we presently lack a good understanding of the reasons why parents make certain foods available to their children. Knowing upon what basis parents make decisions about exposing their children to foods is a necessary prerequisite to addressing parental food choices and therefore children’s exposure to foods. Adults in general consider a broad range of factors including taste, price, health and convenience( Reference Steptoe, Pollard and Wardle 6 , Reference Eertmans, Victoir and Notelaers 29 – Reference Januszewska, Pieniak and Verbeke 31 ) when making food choices. However there may be particular patterns of food choice motives unique to parents. Two recent studies from Scandinavia add to our understanding of parental food choice motives in those countries( Reference Roos, Lehto and Ray 32 , Reference Oellingrath, Hersleth and Svendsen 33 ). It may be expected, though, that differences will exist between parental food choice motives across countries and sociodemographic groups( Reference Eertmans, Victoir and Notelaers 29 , Reference Januszewska, Pieniak and Verbeke 31 ) and research in different population groups is needed.
In the present study we aimed to examine parental food choice motives in a group of Australian mothers of 2–5-year-old children with the view to extending previous work reporting associations between parents’ food choice motives and children’s food intakes( Reference Roos, Lehto and Ray 32 , Reference Oellingrath, Hersleth and Svendsen 33 ) by examining whether parents’ food choice motives were related to children’s food preferences. Furthermore, the effects that different eating occasions have on parents’ food choice motives has not previously been examined extensively, despite evidence that children eat different foods at different eating occasions such as snacks and evening meals( Reference Skinner, Ziegler and Pac 34 , Reference Ziegler, Briefel and Ponza 35 ). We addressed this gap by examining parental food choice motives for children’s snacks and evening meals.
The focus in the present study was therefore on describing a broad range of factors that may affect parents’ reasons for selecting their pre-school children’s foods in two eating contexts (evening meal and snack) and on examining relationships between the motives and children’s food preferences. Information on parents’ food choice motives in different samples and their associations with children’s food preferences may help to inform recommendations and strategies targeted at parents aimed at shifting children’s food preferences and intakes closer to health recommendations.
Method
Study design
The data reported here formed part of a larger investigation of parental influence on children’s food preferences, and the methodology has been reported in detail elsewhere( Reference Russell and Worsley 11 ). In brief, a convenience sample of parents was recruited from various sporting and child-care centres in two medium-sized Australian cities (Melbourne, 44·20 % and Adelaide, 55·80 %). In order to recruit parents and children from a variety of socio-economic levels, centres were selected from three socio-economic groups in each city by selecting suburbs in the bottom, middle and top quintile of the Socio-Economic Index for Areas (SEIFA) Index of Relative Socio-Economic Advantage/Disadvantage (a composite measure of the incomes and the skill level of the workforce)( 36 ). Parents of children aged between 2 and 5 years were targeted in these centres and given a self-completion questionnaire, an information letter and a consent form. A copy of the questionnaire is available from the authors.
The study was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving human subjects/patients were approved by the Deakin University Human Research Ethics Committee (EC 84–2004). Written informed consent was obtained from all participants.
Instrument
The questionnaire covered the child’s liking of 176 foods and drinks chosen to cover the range of foods consumed in Australia (measured on a 5-point Likert scale, anchors of ‘dislike extremely’–‘like extremely’ with the additional options of ‘never tried’ and ‘do not know’), sociodemographic indicators (parent’s education level, postcode and child’s sex) and parents’ food selection criteria. Parents’ food selection criteria were derived from the Food Choice Questionnaire (FCQ)( Reference Steptoe, Pollard and Wardle 6 ). In its original form, the thirty-six items in the FCQ are clustered into the nine factors of Health, Mood, Convenience, Sensory Appeal, Natural Content, Price, Weight Control, Familiarity and Ethical Concern. The FCQ has been used extensively across a number of different population groups (e.g. references Reference Eertmans, Victoir and Notelaers29–Reference Roos, Lehto and Ray32). In the present context the wording of some items was modified so that it was couched in terms of the child. For instance, ‘is what I usually eat’ was changed to ‘is what s/he usually eats’. The item ‘is like the food I ate when I was a child’ was removed as it was irrelevant to this sample. Six items based on a study of parents’ reasons for serving foods were added: ‘is what other family members like’, ‘is good quality or fresh’, ‘is what I like’, ‘is what she/he likes’ and ‘provides food variety’( Reference Koivisto and Sjöden 37 ). The items ‘is part of his/her habit or routine’ and ‘is advertised on TV’ were also included based on literature suggesting they may be important influences on parents’ food selections( Reference Grusec 38 , Reference Aktas 39 ). Respondents were asked to respond to the question ‘It is important to me that the food I choose for my child for a typical snack or evening meal…’ and rate each of the forty-four food choice items on a 4-point scale (‘not at all important’/‘a little important’/‘moderately important’/‘very important’).
Data analyses
All statistical analyses were carried out using the statistical software package SPSS for Windows release 12·0 (2004) and, to reduce the likelihood of Type 1 error, an α level of P<0·01 was selected for statistical significance testing. Descriptive statistics (means and standard deviations) were extracted to determine the relative importance of the individual motive items. Food choice motives were then examined with exploratory factor analysis (principal components with varimax rotation) as the factor structure of the FCQ varies across different populations( Reference Eertmans, Victoir and Notelaers 29 ). An item was considered to load on a given factor if the absolute factor loading was ≥0·40 on that factor and<0·40 on all other factors( Reference Munro 40 ). Pair-wise deletion of variables was employed. Differences in parents’ food choice motivations by socio-economic status (SES) and parental education level were examined with one-way and two-way ANOVA.
Relationships between parents’ food selection criteria (factors) and children’s food preferences were examined via linear regression analyses. Measures of food preferences were: (i) mean liking for the foods within each Australian Guide to Healthy Eating food group (including Extra Foods, which are non-core, low-nutrient, high-energy foods to be eaten in moderation); and (ii) a Healthy Preference Index (HPI)( Reference Russell and Worsley 11 ). The HPI was constructed by summing scores constructed to reflect each of the ten Australian Guide to Healthy Eating recommendations (e.g. eat plenty of vegetables and legumes, enjoy a wide variety of nutritious foods) to provide an overall indicator of how well children’s food preferences aligned with dietary recommendations. A description of the construction of the HPI can be found in Russell and Worsley( Reference Russell and Worsley 11 ). The κ statistic( Reference Cohen 41 ) was used to examine similarity between motives for the snack and evening meal contexts and Pearson correlations tested associations between parents’ motives and the number of untried foods.
Results
Demographic characteristics of the sample
Demographic characteristics of the sample (n 371) are described in Table 1. Briefly, most respondents were mothers or female carers, over 90 % of whom were married or in de facto relationships. Over half of the parents were university graduates and there was broad representation of the five SES strata. Most parents were in full- or part-time employment. Over two-thirds of the children were 4 and 5 years of age and the sexes were evenly balanced. Broadly, the parental sample was representative of the Australian adult population although the sample was better educated( 42 ).
Table 1 Demographic characteristics of the sample of parents (n 371) of 2–5-year-old children, Melbourne and Adelaide, Australia
* Cells may not add up to 100 % due to missing data or rounding.
Description of parents’ motives for the selection of their children’s snack foods
The κ statistics indicated significant (P<0·001) agreement between each of the forty-four items on parents’ food selection criteria for their child’s snack and for the evening meal; hence for brevity only the snack food items are presented here.
As shown in Table 2, taste and nutrition were important motivators for parents when selecting their children’s foods. Over 90 % of the sample thought it was ‘moderately’ or ‘very’ important that their child’s snack food ‘keeps him/her healthy’, ‘is nutritious’ and ‘is good quality or fresh’. It was also highly important to parents that the food they select for their children ‘tastes good’ (<90 % rated as ‘very’ or ‘moderately’ important). A large percentage of parents (85·10 %) indicated that the motive ‘is what s/he likes’ was also very or moderately important to them while ‘is what I like’ or ‘what other family members like’ were less important motives. The motive ‘is what s/he asks me for’ was considered to be ‘moderately’ or ‘very’ important by approximately half of the sample. The majority (>90 %) of parents indicated that the food being advertised on TV was ‘not at all’ or ‘a little important’ to them when selecting foods for their children’s snacks. Approximately three-quarters of parents indicated that a food being ‘cheap’ or ‘not expensive’ was not or of little importance to them.
Table 2 Summary statistics from the exploratory principal components analysis of parents’ snack food choice motive items; sample of parents (n 371) of 2–5-year-old children, Melbourne and Adelaide, Australia
The structure of parent’s motives for selecting their children’s snack foods
Eleven components were extracted from the exploratory principal components analysis of parents’ motives for selecting foods for their children, explaining 62·65 % of the variance and they were interpretable. The Kaiser–Meyer–Olkin Measure of Sampling Adequacy was 0·88 and Bartlett’s test of sphericity was significant (P<0·01). The factors and descriptive results from the factor analysis are reported in Table 3. Cronbach’s α ranged from 0·89 to 0·52 for the extracted factors. With regard to the importance given by parents to each of the factors when selecting foods for their children’s snacks, the eleven extracted factors differed in the mean rating of importance over the individual items comprising the factor. It can be seen in Table 3 that for the largest factor, Health and Nutrition, the mean importance rating in food choice for the individual items was 3·17 (sd 0·53).
Table 3 Descriptive results from the factor analysis of parents’ snack food choice motive items; sample of parents (n 371) of 2–5-year-old children, Melbourne and Adelaide, Australia
The results in Table 2 show that the individual items in this factor were rated by the majority of parents as being ‘moderately important’ or ‘very important’ motives when selecting foods for their children’s snacks. The other extracted factors had lower mean importance ratings for the individual items and smaller percentages of parents rating the individual items as ‘moderately’ or ‘very’ important. For example, the factor Price had a mean of 2·16 (sd 0·72) and it can be seen in Table 2 that two of the three individual items comprising this factor were rated by approximately one-quarter or less as ‘moderately important’ or ‘very important’ for the parent when choosing snack foods for the child.
Children’s food preferences
The children’s liking for each of the food groups is shown in Table 4. Children liked the non-core Extra Foods and Cereals groups the most, and the Vegetables group the least.
Table 4 Children’s mean liking for each food group from the Australian Guide to Healthy Eating, measured on a 5-point Likert scale (1=‘dislike extremely’, 5=‘like extremely’); sample of parents (n 371) of 2–5-year-old children, Melbourne and Adelaide, Australia
a,b,cFood groups with unlike superscript letters were significantly different (P<0·01).
Relationships between parents’ food choice motives and children’s food preferences
In Table 5 the results of the linear regression analyses are documented. The factor Child’s Wants was significantly associated with lower liking of Vegetables, Fruit and Cereals, while the Health and Nutrition factor was associated with slightly greater liking of Vegetables and Fruit. The Natural/Ethical factor was also associated with greater liking of Vegetables and Fruit, while Convenient to Prepare was associated with greater liking of Cereals.
Table 5 Results from linear regression analyses showing relationships between parents’ food choice motives and measures of children’s food preferences; sample of parents (n 371) of 2–5-year-old children, Melbourne and Adelaide, Australia
HPI, Healthy Preference Index.
Significant P values are indicated in bold font.
The factor Child’s Wants was also negatively correlated with the number of foods children had not tried (r=–0·17, P<0·01). None of the other food choice motive factors were significantly associated with the number of untried foods (r ranged from −0·12 to 0·10, NS).
Relationships between parents’ food choice motives and demographic variables: child’s age and sex, socio-economic status and parental education
No statistically significant differences were observed in parents’ food choice motives factor scores by the child’s age (probabilities ranged from 0·04 to 0·87) and sex (probabilities ranged from 0·04 to 0·97). Differences in parents’ food choice motives by SES and parental education level were also not observed (data not reported). The one exception was that parents who had not completed high school scored higher on the factor Child’s Wants (F(2, 291)=4·92, P<0·01) than those who had completed university/tertiary education.
Discussion
When selecting foods for their children, parents were primarily motivated by the child’s needs and wants such as health and nutrition and the child’s liking of the food’s taste. Other factors not directly connected to the child (such as price or ethics) were considered less important. Parents’ food choice motives associated with children’s food preferences in two main ways. These were: (i) that parents who were more motivated by natural/ethical concerns had children with healthier patterns of food preferences; and (ii) that parents who were motivated by their child’s desires had children with unhealthier patterns of food preferences. While associations between parents’ health motivations and children’s healthier food preferences trended towards statistical significance, many of the other parental food choice motives were not predictive of children’s food preferences.
Child-centred motives
The child’s needs and desires were of principal concern for parents. Children’s liking of a food’s taste was among the most important considerations for parents when selecting foods for their children: more than 90 % of the sample indicated that it was ‘very’ or ‘moderately’ important to them that they selected foods for their children that they already liked. Many parents were also influenced by their child’s food requests, with ‘is what s/he asks me for’ considered ‘very’ or ‘moderately’ important by approximately half of the parents in the present study. These results confirm and expand earlier findings noting the influence of children’s food preferences and requests for food on parents’ food decisions( Reference Maubach, Hoek and McCreanor 43 – Reference Koivisto and Sjödén 45 ) by elaborating on the importance of this motive relative to other competing criteria such as health, cost and ethical considerations. Furthermore, we have shown that the Child’s Wants factor (selecting foods in line with the child’s desires) was not only an important motive for parents, but was also associated in negative ways with children’s food preferences (i.e. low liking for fruit, vegetables and cereals and greater numbers of untried foods).
These results may be an indication of the central and possibly negative influence of children upon some parents in the socialisation of children’s eating. Child-centredness in feeding may be counterproductive to the development of healthy food preferences, as selecting for children those foods that they already like or are familiar with may hinder exposure to new foods and those foods that may require several tastings to become liked, such as vegetables( Reference Birch and Marlin 16 , Reference Wardle, Herrera and Cooke 23 , Reference Birch 46 ). In the present study the Child’s Wants motive was linked with children having tried fewer foods, supporting the notion that parents who prioritise this factor offer their children a narrower range of foods. Furthermore, children often have greater preferences for foods higher in salt( Reference Bouhlal, Chabanet and Issanchou 47 ), sugar( Reference Liem, Mars and De Graaf 48 ), energy density and fat content( Reference Birch 49 , Reference Ricketts 50 ) and so it is expected that their food requests are for these types of foods( Reference Jensen 51 ). This, coupled with evidence showing that allowing children freedom to eat what and when they wish or providing children with many food choices is associated with less healthy patterns of food intake in children( Reference Vereecken, Haerens and De Bourdeaudhuij 52 , Reference Hendy, Williams and Camise 53 ), suggests that allowing children to influence parental food choices may result in unhealthy patterns of food preferences and intakes. Also of importance was that in the present research greater child-centredness in food selection was linked with lower parental education levels, suggesting that lower-SES parents, who tend to have children at greater risk of unhealthy eating( Reference Campbell, Crawford and Jackson 54 ), may be more likely to adopt this feeding approach.
Health and nutrition motives
Although children’s desires were important to parents when selecting their children’s foods, health and nutrition were rated as the most important motives by parents in this sample. However, the Health and Nutrition factor only trended towards statistical significance in tests of associations with children’s food preferences. Although the present cross-sectional research cannot determine directionality of effect, it does suggest that a gap exists between parents’ health-related food choice motives and children’s food preferences. Notwithstanding the limitation of relying on parents’ reports and a possible social desirability bias in reporting health motivations, it is conceivable that being motivated by health and nutrition may not have related to actual provision of more healthy foods to the child( Reference St John Alderson and Ogden 55 ). There are several possible reasons for this discrepancy, such as competing demands between the provision of healthy foods and other factors such as time pressures( Reference Maubach, Hoek and McCreanor 43 ) or the competing interests of selecting foods in line with the child’s desire or requests for other foods. It is also feasible that parents lack the necessary nutrition knowledge to be able to select healthy foods for their children( Reference Peters, Sinn and Campbell 24 ). However parental health motivations have been linked with children’s healthier diets( Reference Roos, Lehto and Ray 32 ). An alternative explanation, then, is that parents who are motivated to choose healthy foods for their children inadvertently present these foods to children in ways that promote disliking (e.g. rewarding children for eating them( Reference Peters, Sinn and Campbell 24 , Reference Galloway, Fiorito and Francis 56 )), which would allow for greater intake but not greater liking of healthy foods. The weak associations between parental health motivations and children’s healthier patterns of food preferences do point to a need to better understand the barriers parents face in offering healthy foods to their children and encouraging their children to like such foods.
Natural and ethical motives
Parents’ scores on the Natural/Ethical food motive factor were associated with children’s healthier food preferences (greater liking of vegetables and fruits). It is unknown why these types of motives may be associated with children’s healthier food preferences (instead of health motives). Scores on this factor were not associated with the sociodemographic variables measured here. We speculate that parents who consider natural and ethical criteria when selecting foods may be characterised by a particular value set (e.g. environmentally concerned) or knowledge base (e.g. on how food products are made or how children develop their food preferences), which may make the appropriate provision of healthy foods to their children more likely. Future investigations of such motives may provide additional understanding of the beliefs and behaviours of this group of parents.
Sociodemographics and cost considerations
We expected that cost considerations in food choice could be important to parents, as they are to the general adult population (e.g. references Reference Steptoe, Pollard and Wardle6, Reference Januszewska, Pieniak and Verbeke31, Reference Koivisto and Sjöden37, Reference Cox, Anderson and Lean57–Reference Lennernäs, Fjellström and Becker59). This was not the case, however, with price being rated among the least important motives for parents in the present study. Working mothers are less likely to rate price as an important consideration in selecting foods for the family( Reference McIntosh, Kubena and Tolle 60 ) and approximately half of our sample was working in either full- or part-time employment. However, price was also one of the least important motives in two Scandinavian studies of parental food choice motives( Reference Roos, Lehto and Ray 32 , Reference Oellingrath, Hersleth and Svendsen 33 ) lending weight to the notion that price is less of a consideration than other factors for parents, possibly because of the high priority parents give to children’s desires, health and nutrition. We also observed few differences in the food selection motives by parental education level or SES, confirming the findings of others( Reference Roos, Lehto and Ray 32 , Reference Oellingrath, Hersleth and Svendsen 33 ). Socio-economic factors can be significant in the quality of children’s diets( Reference Campbell, Crawford and Jackson 54 ) and therefore differences may also be expected in parental motives. It appears, though, that parents are similarly motivated across sociodemographic groups although their actual food choices may differ. It should also be noted that many of the other measures of parental food choice motives were not associated with children’s food preferences either, suggesting more general gaps between parents’ motivations and their feeding behaviours. A better understanding of the barriers towards provision of healthy foods to children is needed to better understand how parental motives translate into food purchases and feeding behaviours.
Eating context
We also expected to see differences between the motives of parents when choosing children’s snack foods and when choosing foods for the evening meal. However, of the forty-four possible reasons for selecting foods examined here, none was significantly different in importance between the two eating contexts, suggesting that parents use similar criteria for different eating contexts. This is despite likely differences in the location, company and types of foods that may be consumed( Reference Skinner, Ziegler and Pac 34 , Reference Campbell, Crawford and Jackson 54 ). This result suggests that parents’ food choice motives may be more overarching, perhaps being reflective of general beliefs or values rather than context-specific food selection criteria. Others have also noted that parental attitudes to feeding remain consistent over time and context yet feeding behaviours vary( Reference Hendy, Williams and Camise 53 ).
Instrument structure
Finally, it is also worth noting that when used in this parent sample, the factor structure of the modified FCQ differed in some ways from the original one of Steptoe et al.( Reference Steptoe, Pollard and Wardle 6 ). These were: (i) the existence of three additional factors, namely Quality, Others’ Preferences and Child’s Wants factors; (ii) the Convenience factor appeared as separate Preparation and Purchasing factors in the current study whereas it appeared as one factor in Steptoe et al.’s study( Reference Steptoe, Pollard and Wardle 6 ); and (iii) the Natural and Ethical Concern factors were combined. Roos et al. also noted that Ethical Concern was combined with Health in their study of parents’ food choice motives for the family( Reference Roos, Lehto and Ray 32 ). Although differences would be expected from the original version of the FCQ due to the modification of the questionnaire for the current study, it is likely that parents may have different patterns of motives from the general adult population as they are feeding children, not only themselves. For example, parents in countries like Australia, who are typically time-poor, may be more affected by convenience in preparation as opposed to consumption (which is to be done by the child), and this distinction is seen here. Similarly, the existence of the factors related to the child’s desires and preferences of others may reflect the parental concern for the competing needs of children and other family members. Our results suggest that future studies of parental food choice motives may benefit from using a modified version of the FCQ to capture the motives unique to parents.
Limitations
The current study is limited by several factors inherent to cross-sectional self-report surveys. First, the design does not permit determination of directionality in the relationships observed. Further, parents reported on both their motives and children’s food preferences, thus increasing the likelihood that results are affected by reporting bias. Additionally, the study was conducted on a convenience sample of parents in two Australian cities and further studies of larger, representative samples across different regions and demographic groups are warranted.
Conclusions
Children’s desires (e.g. food likes) and needs (e.g. health) were among the top motives for parents when selecting foods for their children to consume. However, although parents reported being highly motivated by health and nutrition, such motives did not translate convincingly into children’s healthier food preferences. Importantly, parents who reported being influenced by their children’s desires such as their current food preferences and food requests had children with less healthy food preferences. The latter association suggests that children’s food preferences and requests appear to be not only an important determinant of their own food choices, but also those of their parents. Interventions targeted at parents should consider educating parents about strategies for translating their health motivations into healthy food choices and feeding practices for managing their children’s extant preferences and requests for foods.
Acknowledgements
Financial support: C.G.R. was funded with a VicHealth/National Heart Foundation PhD Scholarship. The funders had no role in the design, analysis or writing of this article. Conflict of interest: None. Authorship: C.G.R. and A.W. conceived the study, participated in its design and coordination and helped to draft the manuscript. D.G.L. helped to draft the manuscript. All authors read and approved the final manuscript. Ethics of human subject participation: The Deakin University Human Research Ethics Committee provided approval for the study (EC 84–2004).
