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food for the brain

Championing optimum nutrition for the mind

Q&A on the child survey

SURVEY Q&A

Below are answers to questions regarding the Food for the Brain Child Survey published in 2007. We appreciate your comments, questions and feedback to help improve the quality of this survey. We are extremely grateful to Organix for their donation to fund this first analysis of the data and are seeking funds to further analyse the results of this ongoing survey. If you have any further questions please email info@foodforthebrain.org.

Q How do you know the differences between children with good or bad diets and good or bad SAT scores weren’t simply reflecting differences in socio-economic background?

A On page 33, section 10.2 the issue of the confounding variable of socio-economic background is addressed. It states “It is often suggested that the location of children in traditionally ‘richer’ areas or with a greater incidence of independent schools is a confounding factor in surveys such as this. An analysis of the Sat Scores for the sample across the regions represented shows the distribution of Sat scores for this (self selected and not representative) group based on location. With the exception of east Midlands and Scotland there were no statistically significant variances across the regions for this sample. A review of dietary intakes across the regions for the sample found limited statistically significant variances in intakes for this group of respondents. This reinforces the likelihood that this study is showing the actual effect of foods on children rather than any regional dietary trends or regional educational differences.” The on-line questionnaire has since been adjusted to include more questions relevant to such potentially confounding variables and we are seeking further funding to further analyse this data.

Q The sample size is 10,222 but SAT data are available for 3139. Were the index questions that form the basis for the claims answered for the full sample?

A Yes. All data, except for comparisons to SAT scores, are based on a sample size of 10,222. That is made clear on page 6 ‘with a sample size of 10,222, of which 3,139 (30%) have provided standardised assessment test (SAT) score data, this represents the largest survey on the nutrition and mental health of british school children ever conducted.’

Q The graph in 4.2.1 is supposed to show a "direct and consistent increase in SAT scores with improving diet", but only the top group looks like a real effect. Can you tell me what the Standard Deviations and sample sizes are for this chart?

A The sample sizes are as follows:

 

Group Sample Standard Deviation
Very Good 42 1.21
Good 868 1.14
Neutral 1706 1.16
Poor 482 1.18
Very Poor 32 1.18

 

The difference between the the SAT scores of those with the very poor diets and those with the very good diet was 11% (p>0.05).This data suggests a trend towards increasing SAT scores with improving diet, not a direct and consistence increase. We accept this criticism.

Q What do you mean by ‘effect’ sizes? And are there Standard Deviations for any of these values?

A The ‘effect sizes’ were calculated by looking at the prevalence of respondents in each (high or low) consumption band giving a ‘very good’ rating. The increase or decrease in prevalence between the two represents the ‘effect size’. This represents the increase (or decrease) in likelihood of a very good rating. The comparisons were only made where the variances in prevalence were statistically significant (shown by the colour bandings). We have not calculated standard deviations for these values. We accept that this grid may be trying to ‘do too much’ and we may have compromised on clarity by perhaps trying to be too concise. We are looking at a simpler mechanism that will more clearly show the dramatic difference between consumption groups and the apparent effect of increasing consumption of different foods on stated overall health, stated academic behaviour, SAT scores and a series of everyday symptoms.

Q Were there gender differences in the SAT score data?

A There were no statistically significant gender variances in the SAT score data. The data in 6.3 represents parental subjective view of academic performance and this may (or may not) include other subjective views of academic performance aside from SAT scores - (see para 3.5 in the report that confirms this and explains use of total sample for this high level report).

Para 7.3 reports improved academic performance of children who eat a portion of nuts/seeds per day. However, in the table in para 8, only 1% of the sample achieved this. How many children is this? Were these, and other small sub-set comparisons statistically significant? The highest effect has been singled out (2-3 per week) but ignored the fact that higher nut consumption was associated with lower scores.

A 92 children reported eating nuts and seeds every day. The ‘3-5’ and ‘at least once a day’consumption groups did not show a statistically significant effect on SAT scores in this case. The only statistically significant finding was reported, stating “regular consumption of fresh, raw nuts and seeds is associated with a statistically significant (p<0.001) 7% increase in mean SAT scores at a consumption level of 2-3 times per week.” This trend is consistent with those found in relation to parents rating of behaviour and academic performance.

Q 10.1 is interesting because it would have been helpful if they had indicated how many children fell into each group so that we might have some idea of the samples. It seems as if the 'very good diet' group would have to be part of the subset of children who are in the 6% who eat oily fish 3+ per week, 2% who frequently eat dark green veg, and 1% who eat nuts/seeds daily. They are already members of the SAT set which excludes both younger (<7) and older (14+) children.

A Yes. All data, except for comparisons to SAT scores, are based on a sample size of 10,222. That is made clear on page 6 ‘with a sample size of 10,222, of which 3,139 (30%) have provided standardised assessment test (SAT) score data, this represents the largest survey on the nutrition and mental health of british school children ever conducted.’

Q The graph in 4.2.1 is supposed to show a "direct and consistent increase in SAT scores with improving diet", but only the top group looks like a real effect. Can you tell me what the Standard Deviations and sample sizes are for this chart?

A The sample sizes are as follows:

 

Group

Sample
Very Good 42
Good 868
Neutral 1706

Poor

482
Very Poor 32

 

While these are small sample sizes the difference was statistically significant.

Q The word "variance" seems to be used throughout not in the usual statistical sense of the word. Am I right in supposing that it is being used here as a synonym for 'difference'?

A Yes.