A C TA Obstetricia et Gynecologica
AOGS M A I N R E SE A RC H A R TI C LE
Relative validity and reproducibility of a food frequency questionnaire used in pregnant women from a rural area of China MIN LI1,2, THORHALLUR I. HALLDORSSON3,4, ANNE A. BJERREGAARD3, YAN CHE2, YANYAN MAO2, WENFU HU5, YU WANG6, WEIJIN ZHOU2, SJURDUR F. OLSEN3 & MARIN STRØM3 1
School of Public Health, Fudan University, 2Department of Epidemiology and Social Science on Reproductive Health, National Population and Family Planning Key Laboratory of Contraceptive Drugs and Devices, Shanghai Institute of Planned Parenthood Research, Shanghai, China, 3Center for Fetal Programming, Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark, 4The Unit for Nutrition Research, Faculty of Food Science and Nutrition, School of Health Sciences, University of Iceland, Reykjavik, Iceland, 5Minle Maternal and Child Health Care Center, and 6 Department of Nutrition and Food Hygiene Institute, School of Public Health, Lanzhou University, Gansu, China
Key words Food frequency questionnaire, dietary recall, relative validity, reproducibility, pregnancy Correspondence Weijin Zhou, Shanghai Institute of Planned Parenthood Research, 2140 Xietu Road, Shanghai 200032, China. E-mail: [email protected] Conflict of interest The authors have stated explicitly that there are no conflicts of interest in connection with this article. The authors alone are responsible for the content and writing of the article. Please cite this article as: Li M, Halldorsson TI, Bjerregaard AA, Che Y, Mao Y, Hu W, et al. Relative validity and reproducibility of a food frequency questionnaire used in pregnant women from a rural area of China. Acta Obstet Gynecol Scand 2014; 93: 1141–1149. Received: 17 November 2013 Accepted: 9 July 2014 DOI: 10.1111/aogs.12460
Abstract Objective. Food frequency questionnaires are relatively inexpensive, easy and quick to administer, but the construction of a food frequency questionnaire that can capture Chinese food habits is challenging given the diverse lifestyle and eating habits in different parts of the country. The aim of this study was to assess the validity and reproducibility of a self-administered food frequency questionnaire against a 3-day dietary recall in a rural region of western China. Design. Prospective cohort study. Setting. Chinese maternal and child healthcare hospital. Population. A total of 168 healthy pregnant women. Methods. Pregnant women completed a food frequency questionnaire at 16–24 weeks gestation, and again at 29–31 weeks; during weeks 26–27 they completed a 3-day dietary recall. Results. In general, mean intake was higher when assessed with food frequency questionnaires compared with dietary recall. Spearman and intra-class correlation coefficients between the two food frequency questionnaires ranged from 0.31 to 0.69 and from 0.27 to 0.79, respectively. For the second food frequency questionnaire and the dietary recall, the crude and de-attenuated Spearman correlations ranged from 0.12 to 0.55 and 0.14 to 0.58, respectively. The correlation both between the two food frequency questionnaires and between the second food frequency questionnaire and the dietary recall decreased after adjustment for energy. Ranking women, 31–57% and 1–8% were classified into the same and the opposite quartile, respectively, by both food frequency questionnaires; 30–45% and 1–11% were classified into the same and the opposite quartile respectively for the second food frequency questionnaire and dietary recall. Conclusion. The food frequency questionnaire showed good reproducibility and correlations with dietary recall; it is useful for ranking study participants according to dietary intake, which is of great importance to future etiological studies in this cohort. DR, dietary recall; FFQ, food frequency questionnaire; FOS, fish oil supplementation; GW, gestational week.
Abbreviations:
ª 2014 Nordic Federation of Societies of Obstetrics and Gynecology, Acta Obstetricia et Gynecologica Scandinavica 93 (2014) 1141–1149
1141
Validity and reproducibility of an FFQ
Introduction Maternal diet during pregnancy is of considerable importance for maternal infant health and development (1). However, studies are complicated because comprehensive dietary assessment methods are often expensive, time consuming and require a high commitment from participants (2). Food frequency questionnaires (FFQs) are relatively inexpensive, easy and quick to administer (3,4), and have been increasingly used in epidemiological studies to assess long-term diets of different populations including pregnant women in both developed countries and China (5,6). The construction of an FFQ that can capture Chinese food habits is challenging given the diverse lifestyle and eating habits in different parts of the country (7). Validation of such an assessment instrument among pregnant women is of importance, because it provides valuable insights into the strengths and weaknesses of using FFQs for epidemiological studies in China. The aim of this study was to describe the dietary habits of pregnant women in a rural region in China and to assess the relative validity and reproducibility of a self-administered, 80-item, semi-quantitative FFQ against a dietary recall (DR) covering the previous 3 days.
Material and methods In 2007, three of the authors (S.F. Olsen, W. Zhou and M. Li) initiated a population-based cohort study of pregnant women and assessed dietary intake in pregnancy. The women were originally recruited for a double-blinded randomized controlled trial investigating the effect of fish oil supplementation (FOS) in pregnancy on birth outcomes in areas of China where fish intake is low. The target was to include >5000 pregnant women in the FOS trial, and we assessed the dietary intake of pregnant women by use of a semi-quantitative FFQ at recruitment around gestational weeks (GW) 16–24. Participants in this validation study were enrolled while attending a prenatal examination at the Maternal and Child Health Care Hospital of Min Le County, Gansu Province, one of the sites of the FOS trial. Min Le County is in the northwest area of China, at the foot of the Qiliang Mountain, with an average temperature of 4.1°C through the year. Data were collected between June 2011 and September 2011. Of 422 potential participants from the FOS trial who fulfilled the inclusion criteria 200 pregnant women were invited to take part in the study. Of these, 184 (92%) agreed to participate, while 13 doubted the safety of the trial and two gave no reason for not wanting to participate. Among the 184 eligible pregnant women who were
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recruited for this validation study 16 (9%) dropped out due to miscarriage (n = 3) or moving to another area (n = 11), while two gave no reason for dropping out. Hence, a total of 168 women completed the validation study by filling out two repeated FFQs and a 3-day DR conducted by trained personnel. Demographic information and the first FFQ were collected at the time of recruitment (GW 16–24); the DR was conducted during GW 26–27; and the second FFQ was completed during GW 29–31. In the two FFQs women were asked to report their dietary intake during the three previous months. The FFQ food list was developed based on food reports in 24-h DRs collected from 50 participants in the study county before the validation study. As there might be large variation in recipes used for mixed dishes between households, and because a Chinese meal traditionally consists of several dishes, the FFQ was composed of food items rather than recipes for whole dishes. The FFQ included questions covering 11 different food groups and 82 different food items in total (for detailed list see Appendix S1). The frequency categories for each food item ranged from: never to more than three times a day. The portion sizes for all solid food items were listed as 1 Liang (which is a unit of weight commonly used in China, corresponding to 50 g) to >5 Liang in 1-Liang increments. For eggs the listed portion sizes were 60 g (one egg) to >300 g (five eggs) in 60-g (one-egg) increments. For beverages the portion sizes listed were 125 mL (a small cup) to >625 mL in 125-mL increments. Participants were asked to choose their portion sizes according to provided photographs (8). The participants were asked to return to the hospital in GW 26–27 for the DR and were asked to keep a record of their dietary consumption for the three previous days. At the hospital a trained interviewer registered the total food intake during the three previous days, including two working days and one weekend day. The respondents were assisted in their estimation of portion sizes with a book of photographs of commonly consumed foods. For the FFQ, daily intake of specific food items was calculated by multiplying the frequency of consumption with the chosen portion size. We redefined the portion
Key Message A relatively simple food frequency questionnaire can be used to rank Chinese pregnant women according to dietary intake, which is useful for future epidemiological studies focusing on maternal nutrition in rural China.
ª 2014 Nordic Federation of Societies of Obstetrics and Gynecology, Acta Obstetricia et Gynecologica Scandinavica 93 (2014) 1141–1149
M. Li et al.
size >5 Liang to 6 Liang, >300 g to 360 g, and >625 mL to 750 mL, while frequencies that were given as a range were defined as the average of the upper and lower frequencies. Upper limits of five times per day for frequency of consumption were set to avoid extreme intakes by scaling down so the total sum of all items was equal to the upper limit. Portion sizes were missing for eight cases, and these were replaced by the mean portion size among the remaining participants. For the DR the same approach as described for the FFQ was used for food group and nutrient calculations. The mean across the 3 days of recall was used to represent the average intake. The daily nutrient intake was subsequently calculated for both FFQs and the DR using the 2002 and 2004 Chinese Food Composition Table (9,10). Due to skewed intake distributions we present median intake of nutrients and we use nonparametric methods to assess validity of the dietary assessment methods (11). Differences in intakes between two dietary methods were tested using Wilcoxon signed rank test. The ratio between intake estimates derived from the second FFQ and the DR (referent) was used to identify subjects’ over- or under-reporting. Associations between intakes of food groups and nutrients estimated by each dietary method were described using Spearman rank correlation coefficients. Intra-class correlation coefficients (based on one-way analysis of variance) were also calculated between intakes from the two FFQs. To minimize variation in food intake caused by differences in energy intake we energy-adjusted the correlation coefficients by the residual method (12). De-attenuated correlation coefficients between DR and FFQs were calculated to adjust for within-person variation (13). The methods to calculate confidence interval estimates for the correlation coefficient were described by Rosner and Willett (13). To test the agreement between the two FFQs and between the second FFQ and the DR, women were categorized into quartiles according to consumption of individual food groups. The proportion of women classified into the same, adjacent or opposite quartile for both methods was calculated. In all analyses, statistical significance was set as p < 0.05 (two-sided). Statistical Package for Social Sciences for Windows version 16.0 (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses.
Results Table 1 presents the characteristics of the 168 pregnant women included in the validation study. Compared with the total group of participants in the FOS trial (n = 3503), participants in the validation study only differed with respect to age (27 years vs. 23 years in FOS vs. validation study), body mass index (22.3 kg/m2 vs.
Validity and reproducibility of an FFQ
Table 1. Characteristics of the 168 pregnant women who participated in the validation study and comparison to the 3503 cohort members of the fish oil supplementation (FOS) trial. Mean (SD) or % Validation study (n = 168)
FOS trial (n = 3503)
Age (years) 23 (3.1) 27 (4.1) Weight enrolled (kg) 54.2 (6.8) 58.2 (7.7) Height (cm) 160.7 (4.6) 161.4 (4.5) Body mass index (kg/m2) 21.0 (2.4) 22.3 (2.7) Smoking during pregnancy (%) 0.6 0.4 Drinking during pregnancy (%) 0 0.1 Gravidity (%) First 78.6 59.3 Second 17.9 27.1 Third or more 3.6 13.6 Parity First 85.0 87.6 Second 14.4 12.0 Third or more 0.6 0.3 Abortion None 92.2 67.2 Once 6.0 22.3 Twice or more 1.8 10.5
p-valuea
AOGS M A I N R E SE A RC H A R TI C LE
Relative validity and reproducibility of a food frequency questionnaire used in pregnant women from a rural area of China MIN LI1,2, THORHALLUR I. HALLDORSSON3,4, ANNE A. BJERREGAARD3, YAN CHE2, YANYAN MAO2, WENFU HU5, YU WANG6, WEIJIN ZHOU2, SJURDUR F. OLSEN3 & MARIN STRØM3 1
School of Public Health, Fudan University, 2Department of Epidemiology and Social Science on Reproductive Health, National Population and Family Planning Key Laboratory of Contraceptive Drugs and Devices, Shanghai Institute of Planned Parenthood Research, Shanghai, China, 3Center for Fetal Programming, Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark, 4The Unit for Nutrition Research, Faculty of Food Science and Nutrition, School of Health Sciences, University of Iceland, Reykjavik, Iceland, 5Minle Maternal and Child Health Care Center, and 6 Department of Nutrition and Food Hygiene Institute, School of Public Health, Lanzhou University, Gansu, China
Key words Food frequency questionnaire, dietary recall, relative validity, reproducibility, pregnancy Correspondence Weijin Zhou, Shanghai Institute of Planned Parenthood Research, 2140 Xietu Road, Shanghai 200032, China. E-mail: [email protected] Conflict of interest The authors have stated explicitly that there are no conflicts of interest in connection with this article. The authors alone are responsible for the content and writing of the article. Please cite this article as: Li M, Halldorsson TI, Bjerregaard AA, Che Y, Mao Y, Hu W, et al. Relative validity and reproducibility of a food frequency questionnaire used in pregnant women from a rural area of China. Acta Obstet Gynecol Scand 2014; 93: 1141–1149. Received: 17 November 2013 Accepted: 9 July 2014 DOI: 10.1111/aogs.12460
Abstract Objective. Food frequency questionnaires are relatively inexpensive, easy and quick to administer, but the construction of a food frequency questionnaire that can capture Chinese food habits is challenging given the diverse lifestyle and eating habits in different parts of the country. The aim of this study was to assess the validity and reproducibility of a self-administered food frequency questionnaire against a 3-day dietary recall in a rural region of western China. Design. Prospective cohort study. Setting. Chinese maternal and child healthcare hospital. Population. A total of 168 healthy pregnant women. Methods. Pregnant women completed a food frequency questionnaire at 16–24 weeks gestation, and again at 29–31 weeks; during weeks 26–27 they completed a 3-day dietary recall. Results. In general, mean intake was higher when assessed with food frequency questionnaires compared with dietary recall. Spearman and intra-class correlation coefficients between the two food frequency questionnaires ranged from 0.31 to 0.69 and from 0.27 to 0.79, respectively. For the second food frequency questionnaire and the dietary recall, the crude and de-attenuated Spearman correlations ranged from 0.12 to 0.55 and 0.14 to 0.58, respectively. The correlation both between the two food frequency questionnaires and between the second food frequency questionnaire and the dietary recall decreased after adjustment for energy. Ranking women, 31–57% and 1–8% were classified into the same and the opposite quartile, respectively, by both food frequency questionnaires; 30–45% and 1–11% were classified into the same and the opposite quartile respectively for the second food frequency questionnaire and dietary recall. Conclusion. The food frequency questionnaire showed good reproducibility and correlations with dietary recall; it is useful for ranking study participants according to dietary intake, which is of great importance to future etiological studies in this cohort. DR, dietary recall; FFQ, food frequency questionnaire; FOS, fish oil supplementation; GW, gestational week.
Abbreviations:
ª 2014 Nordic Federation of Societies of Obstetrics and Gynecology, Acta Obstetricia et Gynecologica Scandinavica 93 (2014) 1141–1149
1141
Validity and reproducibility of an FFQ
Introduction Maternal diet during pregnancy is of considerable importance for maternal infant health and development (1). However, studies are complicated because comprehensive dietary assessment methods are often expensive, time consuming and require a high commitment from participants (2). Food frequency questionnaires (FFQs) are relatively inexpensive, easy and quick to administer (3,4), and have been increasingly used in epidemiological studies to assess long-term diets of different populations including pregnant women in both developed countries and China (5,6). The construction of an FFQ that can capture Chinese food habits is challenging given the diverse lifestyle and eating habits in different parts of the country (7). Validation of such an assessment instrument among pregnant women is of importance, because it provides valuable insights into the strengths and weaknesses of using FFQs for epidemiological studies in China. The aim of this study was to describe the dietary habits of pregnant women in a rural region in China and to assess the relative validity and reproducibility of a self-administered, 80-item, semi-quantitative FFQ against a dietary recall (DR) covering the previous 3 days.
Material and methods In 2007, three of the authors (S.F. Olsen, W. Zhou and M. Li) initiated a population-based cohort study of pregnant women and assessed dietary intake in pregnancy. The women were originally recruited for a double-blinded randomized controlled trial investigating the effect of fish oil supplementation (FOS) in pregnancy on birth outcomes in areas of China where fish intake is low. The target was to include >5000 pregnant women in the FOS trial, and we assessed the dietary intake of pregnant women by use of a semi-quantitative FFQ at recruitment around gestational weeks (GW) 16–24. Participants in this validation study were enrolled while attending a prenatal examination at the Maternal and Child Health Care Hospital of Min Le County, Gansu Province, one of the sites of the FOS trial. Min Le County is in the northwest area of China, at the foot of the Qiliang Mountain, with an average temperature of 4.1°C through the year. Data were collected between June 2011 and September 2011. Of 422 potential participants from the FOS trial who fulfilled the inclusion criteria 200 pregnant women were invited to take part in the study. Of these, 184 (92%) agreed to participate, while 13 doubted the safety of the trial and two gave no reason for not wanting to participate. Among the 184 eligible pregnant women who were
1142
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recruited for this validation study 16 (9%) dropped out due to miscarriage (n = 3) or moving to another area (n = 11), while two gave no reason for dropping out. Hence, a total of 168 women completed the validation study by filling out two repeated FFQs and a 3-day DR conducted by trained personnel. Demographic information and the first FFQ were collected at the time of recruitment (GW 16–24); the DR was conducted during GW 26–27; and the second FFQ was completed during GW 29–31. In the two FFQs women were asked to report their dietary intake during the three previous months. The FFQ food list was developed based on food reports in 24-h DRs collected from 50 participants in the study county before the validation study. As there might be large variation in recipes used for mixed dishes between households, and because a Chinese meal traditionally consists of several dishes, the FFQ was composed of food items rather than recipes for whole dishes. The FFQ included questions covering 11 different food groups and 82 different food items in total (for detailed list see Appendix S1). The frequency categories for each food item ranged from: never to more than three times a day. The portion sizes for all solid food items were listed as 1 Liang (which is a unit of weight commonly used in China, corresponding to 50 g) to >5 Liang in 1-Liang increments. For eggs the listed portion sizes were 60 g (one egg) to >300 g (five eggs) in 60-g (one-egg) increments. For beverages the portion sizes listed were 125 mL (a small cup) to >625 mL in 125-mL increments. Participants were asked to choose their portion sizes according to provided photographs (8). The participants were asked to return to the hospital in GW 26–27 for the DR and were asked to keep a record of their dietary consumption for the three previous days. At the hospital a trained interviewer registered the total food intake during the three previous days, including two working days and one weekend day. The respondents were assisted in their estimation of portion sizes with a book of photographs of commonly consumed foods. For the FFQ, daily intake of specific food items was calculated by multiplying the frequency of consumption with the chosen portion size. We redefined the portion
Key Message A relatively simple food frequency questionnaire can be used to rank Chinese pregnant women according to dietary intake, which is useful for future epidemiological studies focusing on maternal nutrition in rural China.
ª 2014 Nordic Federation of Societies of Obstetrics and Gynecology, Acta Obstetricia et Gynecologica Scandinavica 93 (2014) 1141–1149
M. Li et al.
size >5 Liang to 6 Liang, >300 g to 360 g, and >625 mL to 750 mL, while frequencies that were given as a range were defined as the average of the upper and lower frequencies. Upper limits of five times per day for frequency of consumption were set to avoid extreme intakes by scaling down so the total sum of all items was equal to the upper limit. Portion sizes were missing for eight cases, and these were replaced by the mean portion size among the remaining participants. For the DR the same approach as described for the FFQ was used for food group and nutrient calculations. The mean across the 3 days of recall was used to represent the average intake. The daily nutrient intake was subsequently calculated for both FFQs and the DR using the 2002 and 2004 Chinese Food Composition Table (9,10). Due to skewed intake distributions we present median intake of nutrients and we use nonparametric methods to assess validity of the dietary assessment methods (11). Differences in intakes between two dietary methods were tested using Wilcoxon signed rank test. The ratio between intake estimates derived from the second FFQ and the DR (referent) was used to identify subjects’ over- or under-reporting. Associations between intakes of food groups and nutrients estimated by each dietary method were described using Spearman rank correlation coefficients. Intra-class correlation coefficients (based on one-way analysis of variance) were also calculated between intakes from the two FFQs. To minimize variation in food intake caused by differences in energy intake we energy-adjusted the correlation coefficients by the residual method (12). De-attenuated correlation coefficients between DR and FFQs were calculated to adjust for within-person variation (13). The methods to calculate confidence interval estimates for the correlation coefficient were described by Rosner and Willett (13). To test the agreement between the two FFQs and between the second FFQ and the DR, women were categorized into quartiles according to consumption of individual food groups. The proportion of women classified into the same, adjacent or opposite quartile for both methods was calculated. In all analyses, statistical significance was set as p < 0.05 (two-sided). Statistical Package for Social Sciences for Windows version 16.0 (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses.
Results Table 1 presents the characteristics of the 168 pregnant women included in the validation study. Compared with the total group of participants in the FOS trial (n = 3503), participants in the validation study only differed with respect to age (27 years vs. 23 years in FOS vs. validation study), body mass index (22.3 kg/m2 vs.
Validity and reproducibility of an FFQ
Table 1. Characteristics of the 168 pregnant women who participated in the validation study and comparison to the 3503 cohort members of the fish oil supplementation (FOS) trial. Mean (SD) or % Validation study (n = 168)
FOS trial (n = 3503)
Age (years) 23 (3.1) 27 (4.1) Weight enrolled (kg) 54.2 (6.8) 58.2 (7.7) Height (cm) 160.7 (4.6) 161.4 (4.5) Body mass index (kg/m2) 21.0 (2.4) 22.3 (2.7) Smoking during pregnancy (%) 0.6 0.4 Drinking during pregnancy (%) 0 0.1 Gravidity (%) First 78.6 59.3 Second 17.9 27.1 Third or more 3.6 13.6 Parity First 85.0 87.6 Second 14.4 12.0 Third or more 0.6 0.3 Abortion None 92.2 67.2 Once 6.0 22.3 Twice or more 1.8 10.5
p-valuea
