Although this study in general showed reasonable comparability between the two questionnaires at the group level, substantial and significant differences were observed. For nutrients, the largest differences were seen for added sugar and vitamin D; where added sugar was reported lower and vitamin D was reported higher in the SFFQ-2007 compared to the SFFQ-1999. Significantly higher intake of E% and absolute intake of fat was also reported in the SFFQ-2007 compared to the SFFQ-1999. For food intake, significant differences were observed for three out of seventeen food groups: lower intake of yoghurt and higher intake of vegetables and fish with the SFFQ-2007 compared to the SFFQ-1999. In addition, reliable answers with regard to breastfeeding status, age for breastfeeding cessation and age for introducing solid foods were found.
As in the study comparing the dietary questionnaires used among Norwegian 2-year-olds in 1999 and in 2007
, the largest difference with regard to nutrients were seen for added sugar, both for absolute intake and E%. A plausible reason for this difference among the 12 month olds was the reduction in the content of added sugar in the commercial baby food products in the period from 1999 to 2007. In the SFFQ-1999 the commercial baby food products were the main source for added sugar, contributing with 51% of the added sugar, while this only contributed with 4% in the SFFQ-2007. For example, the most frequently used commercial baby porridge in both questionnaires had a reduction in added sugar content in this period of time with about 3 grams added sugar per 100 gram prepared porridge. In addition, the added sugar content in commercial fruit purée was reduced with about 16 grams added sugar per 100 gram fruit purée. Even though the commercial baby food products had reduced the content of added sugar in this period of time, many of the products that were on the market in 2007 were still sweet as the added sugar was replaced by dried fruits, fruit concentrate or other components with a sweet taste. However, these compounds are not included in the added sugar. Moreover, as previously reported
, the reduction in sugar content in yoghurt from 1999 to 2007 could also explain this difference in sugar intake as yoghurt was the second most important contributor to the sugar intake in the SFFQ-1999. As added sugar is included in the total intake of carbohydrates, the lower reported intake of added sugar with the SFFQ-2007 compared to the SFFQ-1999 could probably also explain the significant difference in carbohydrate intake between the questionnaires.
Another large difference between the two questionnaires was seen for intake of vitamin D. In the SFFQ-2007 baby food products contributed with 44% of the vitamin D intake, while in the SFFQ-1999 the most important contributor was dietary supplements, contributing with 34% of the vitamin D intake. When the data was analyzed without dietary supplements, intake of vitamin D was still reported significantly higher with the SFFQ-2007 compared to the SFFQ-1999, indicating that dietary supplements could not explain this difference. However, a likely reason for the difference could be the change in vitamin D content in the most frequently used commercial baby porridge in both questionnaires. In 1999 this porridge did not contain vitamin D, while in 2007 this porridge was enriched with 1.2 μg vitamin D per 100 gram prepared porridge.
Commercial baby porridge was an important source of fat in both questionnaires, contributing with 17% and 11% of the fat intake in the SFFQ-2007 and in the SFFQ-1999, respectively. The most frequently used commercial baby porridge in both questionnaires contained more fat in the SFFQ-2007 compared to the SFFQ-1999. The increase in fat content in this period of time was about 1 gram fat per 100 gram prepared porridge, being a reasonable explanation for the differences with regard to fat intake in the two questionnaires.
With regard to food intake, significantly higher intake of yoghurt was reported with the SFFQ-1999 compared to the SFFQ-2007. As previously speculated
, inclusion of the sub-question ‘other fruit-flavoured yoghurt’ in the SFFQ-1999 may have overestimated intake of fruit-flavoured yoghurt in the SFFQ-1999. On the other hand, by not including this sub-question in the SFFQ-2007, the SFFQ-2007 may not have been capable of capturing the intake of all fruit-flavoured yoghurt. The highest frequency option in the SFFQ-1999 (“4 or more times per day”) was not included in the SFFQ-2007 (Table
1). However, this option was not used in the SFFQ-1999, and can thereby not explain the differences in intake between the questionnaires.
Intake of vegetables was reported significantly higher in the SFFQ-2007 compared to the SFFQ-1999. This was also seen among Norwegian 2-year-olds
, and a likely explanation in that study and in the present study was the inclusion of six new sub-questions with regard to intake of vegetables in the SFFQ-2007. Intake of fish was also reported significantly higher in the SFFQ-2007 compared to the SFFQ-1999. This could be due to inclusion of two more sub-questions with regard to fish dinners in the SFFQ-2007 compared to the SFFQ-1999. A higher reported intake with extended number of food items is consistent with the work of Krebs-Smith et al.
, who observed how estimates of fruit and vegetable intake, from FFQs, were affected by the number of fruit and vegetable questions included.
To assist parents in reporting amounts of food eaten, a photographic booklet was used. As shown in Table
1, there were differences to the booklet used in the survey of 1999 and that of 2007. Both intake of sausages and intake of rice were reported lower in the SFFQ-2007 compared to the SFFQ-1999, which might be a consequence of this (data not shown).
In the present study, the correlations between the questionnaires with regard to intake of energy, nutrients and food groups were low to moderate (0.14 – 0.74). Overall, these correlations were lower than the correlations observed among Norwegian 2-year-olds
. The observed correlations for food groups were also lower than those observed in two reproducibility studies of FFQs, one among 124 Flemish children aged 2.5 to 6.5 years
 and one among 130 children from New Zealand, aged 1–14 year
. The lowest correlation observed in the present study was observed for milk (r = 0.14). This could be related to the fact that Norwegian infants, who are not breastfed, are recommended to use infant formula instead of cow’s milk the first 12 months of life
. When data was analyzed with regard to which questionnaire answered first, the mean milk intake was reported approximately 110–120 ml higher in the second questionnaire compared to the first questionnaire filled in. The opposite was found for intake of infant formula, where the highest intake was reported in the questionnaire answered first. When intake of milk and infant formula was analyzed together, the correlation was 0.62. In addition, large differences between the two data-bases with regard to nutrient content of commercial baby food products could also contribute to the lower correlations observed compared to similar studies
[8, 15, 16].
The mean differences between the questionnaires with regard to nutrients and food groups were higher compared to that observed among the Norwegian 2-year-olds
 and higher than that observed for food groups in the reproducibility study among the Flemish children
. Additionally, in most Bland and Altman plots, the limits of agreement were large for all nutrients and food groups, indicating that the agreement at the individual level was of considerable variability.
In a review published in 2005, Li and co-workers
 concluded that mothers seem to provide accurate estimates of initiation and duration of any breastfeeding, especially when the duration was recalled over a period of 3 years or less. In the present study, where the recall period was within a maximum of 12 months after breastfeeding cessation, the mothers seem to accurately report breastfeeding status at 12 months of age (r = 0.82) and the age of breastfeeding cessation (r = 0.97). However, Gillespie et al.
 observed a correlation between breastfeeding duration for 3-week recall opposed to 1 – 3.5 year recall of only 0.59. Analyses were conducted among 124 US women, and limited to those who ceased breastfeeding within the first 3 months, which may have caused a low correlation. With regard to the validity and reliability of maternal recall for the age at introduction of foods and fluids other than breast milk, Li et al.
 concluded that recall was less satisfactory. However, the correlation observed with regard to introduction of solid foods was satisfactory in the present study (r = 0.74).
Strengths and weaknesses of the study
As others have found a tendency of higher reported intake in the first questionnaire compared to the second questionnaire
[15, 16], an important strength of the present study is the cross-over design where the order of the questionnaires did not confound our findings. Even though the cross-over design would minimize changes between the questionnaires, it might be that changes in the diet happen too quickly around the age of 12 months to be ruled out by this design, exemplified with intake of milk in the present study. Moreover, as the time period between answering the questionnaires was within a month’s time, we assume this time to be sufficient so that the participants would not remember their answers from the first questionnaire when filling in the second questionnaire. Another important strength of this study is the possibility to test the reliability of maternal recall of infant feeding practices, which seem to be of satisfactory quality.
In the last few decades, there has been a tendency towards decrease in the response rates of most health studies
. In this study only 31% of the originally drawn sample was willing to participate. Moreover, fewer mothers with low education answered the SFFQ-1999 first, compared to those answering the SFFQ-2007 first, the implication of this needs to be analyzed in a larger study. The participants in the present study had the same mean age and the same level of education as the mothers participating in the national dietary survey among 12 months olds in 2007
. However, as the participation rate was low, it might be that the participants were more interested in diet and more persistent in filling in questionnaires and thereby reporting more accurately than a random sample of families with a 12 month old child.