Health promotion, i.e. the process of enabling people to increase control over and to improve their health, is an increasingly important role of nurses and other health professionals. Weight management is a frequent focus for health improvement and the extent to which health professionals correctly identify their own body weight status may indicate their ability to correctly identify the weight status of their patients. In particular, overweight or obese health professionals who fail to recognize their own weight status may do the same with patients.
The discrepancy between self-perceived weight and actual weight has been revealed by many studies of the lay population from different countries( Reference Chang and Christakis 1 – Reference Yaemsiri, Slining and Agarwal 11 ). A nationally representative sample of the US adult population, the National Health Interview Survey (NHIS, 1991), reported that 29 % of respondents misclassified their weight status relative to medical standards( Reference Chang and Christakis 1 ). Subsequently, a series of National Health and Nutrition Examination Surveys (NHANES)( Reference Chang and Christakis 2 , Reference Bennett and Wolin 3 , Reference Johnson-Taylor, Fisher and Hubbard 7 , Reference Dorsey, Eberhardt and Ogden 10 , Reference Yaemsiri, Slining and Agarwal 11 ) found that weight misperception had been highly prevalent in the US population, with the latest evidence from NHANES 2003–2008( Reference Yaemsiri, Slining and Agarwal 11 ) finding that 23 % of overweight women and 48 % of overweight men perceived themselves as having the right weight. Similar results were observed in two nationally representative surveys from the UK, conducted in 1999 and in 2007( Reference Johnson, Cooke and Croker 8 ), which showed that 19 % and 25 % of overweight and obese people inaccurately perceived themselves to be of normal weight. Also, a randomly selected sample of Greek adults confirmed that the proportion of true positives for correct obesity identification was 62 %( Reference Yannakoulia, Panagiotakos and Pitsavos 4 ). Consistent with the above findings from Western countries, the prevalence of misperception of weight status in East Asian samples has become evident from recent studies. The MY Health Up study conducted in Japan in 2004 found that the percentage of inaccurate weight perception was 39 % in men and 46 % in women( Reference Inoue, Toyokawa and Miyoshi 5 ). This latter finding is very similar to that of the 2001 Seoul Citizens Health Indicator Survey (SCHIS) in South Korea, which found that 43 % of women perceived their weight inaccurately( Reference Kim, Kim and Cho 6 ).
According to a cross-sectional survey of 1614 Chinese female undergraduates, inaccurate perception of weight status is more frequent in women who are underweight than in those who are of normal weight, 83 % and 57 % respectively( Reference Zhang, Wu and Ting 9 ). Moreover, this disparity in inaccuracy of perception of body weight correlates with demographic and socio-economic variables. Generally, those who are female, younger, white, with a higher than average BMI, higher income or higher education are more likely to overestimate their body weight. In addition, individuals’ occupation and health status may be related to weight status misperception( Reference Chang and Christakis 1 – Reference Inoue, Toyokawa and Miyoshi 5 , Reference Dorsey, Eberhardt and Ogden 10 – Reference Jaworowska and Bazylak 15 ). For example, those in managerial or professional occupations were estimated to have lower odds of under-assessing their weight than those in other occupational groups, even after controlling for income and education( Reference Chang and Christakis 1 ).
It could be, of course, that the people surveyed in these studies feel that their weight is actually the ‘right’ weight and therefore there is no misperception on their part. This possibility should be considered especially in the light of research which shows that the health of those who are slightly overweight does not differ significantly from those of ‘healthy’ weight( Reference Auyeung, Lee and Leung 16 ) and also in the light of what is known about BMI and its tendency to overestimate weight status for those who are muscular( Reference Rothman 17 ).
We are aware of only three published research reports which describe the accuracy of self-perceived weight status in health professionals( Reference Perrin, Flower and Ammerman 18 – Reference Kirk, Cockbain and Beazley 20 ), and only one of these examined variables associated with health professionals’ misperceptions of weight status. A cross-sectional survey of 355 US paediatricians reported that 49 % of overweight paediatricians did not identify themselves as overweight; of the covariates examined, only gender and BMI influenced the odds of paediatricians misclassifying themselves as overweight( Reference Perrin, Flower and Ammerman 18 ). Another study of a sample of 138 physicians found that 73 % in the normal weight range accurately perceived their weight status and 76 % of overweight or obese physicians perceived themselves as overweight( Reference Jiménez-Cruz and Bacardí-Gascón 19 ). A similar small study of nurses’ weight perceptions found that fifteen out of thirty-three nurses (45 %) accurately rated their weight categories compared with twelve out of sixty-nine members of the general public (17 %)( Reference Kirk, Cockbain and Beazley 20 ).
The research described in the current paper builds on previous studies to investigate (i) nurses’ agreement between their self-perceived weight status and BMI status and (ii) the relationship between weight status misperception and personal body weight, demographics and health status. It investigates two research questions:
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1. Is there agreement between nurses’ perceived weight status and their estimated BMI status?
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2. What demographic and other personal profile variables are associated with misperceptions of weight status?
Methods
Study design and participants
A cross-sectional survey was undertaken with a convenience sample of 456 student nurses (May–June 2010) and 588 qualified nurses (October–November 2010) attending one large university in London, UK. A self-report questionnaire was distributed to potential participants, who were recruited on a voluntary basis during scheduled class times. Individuals who self-reported pregnancy or breast-feeding were excluded from the study because of the possible impact of this on their perceived body weight. A total of 764 respondents (355 student nurses and 409 qualified nurses) completed questionnaires with a response rate of 73 % (78 % in student nurses; 70 % in qualified nurses).
Study measures
The questionnaire included the following measures, the results of which we report in the current paper.
Sociodemographics
Included in the present analyses were gender, age, ethnicity, height and weight (for calculation of BMI as kg/m2), enrolment programme (only for student nurses), highest education qualification (only for qualified nurses), clinical speciality (only for qualified nurses), work place (only for qualified nurses) and years in practice (only for qualified nurses).
Weight status
This was assessed in two ways. (i) BMI status was calculated from self-reported weight and height data, which were used to categorize participants as underweight (BMI <18·5 kg/m2), normal weight (18·5 ≤ BMI<25·0 kg/m2), overweight (25·0 ≤ BMI<30·0 kg/m2) or obese (BMI ≥ 30·0 kg/m2)( 21 ). (ii) Perceived weight status was collected using the question: ‘How would you describe yourself: thin, normal, overweight or obese?’
Weight status misperceptions
This was defined as the difference between perceived weight status and BMI status. Two types of misperceptions were identified here: (i) underestimation and (ii) overestimation of weight status. Underestimation occurred when individuals’ perceived weight status was less than their BMI status. Overestimation occurred when individuals’ perceived weight status was more than their BMI status. In contrast to weight status misperceptions, correct perception occurred when individuals’ perceived weight status was concordant with their BMI status.
Physical activity
Physical activity was measured by the General Practice Physical Activity Questionnaire (GPPAQ), a well-validated, seven-item, self-report measure( 22 ). This generates a four-level Physical Activity Index (PAI) classifying participants into one of four categories: active, moderately active, moderately inactive or inactive. In the current analyses, two PAI categories (‘moderately inactive’ and ‘inactive’) were combined into one category (‘inactive’) because of a small number of cases.
Family histories of obesity co-morbidities
We collected histories of high blood pressure, hyperlipidaemia, stroke, CHD, diabetes, eating disorders, arthritis and cancer. Respondents were classified into one of three groups according to the number of obesity co-morbidities identified: 0, 1–2 or ≥3.
Testing and reliability of the questionnaire
The questionnaire was pilot tested in two small samples, both of which were independent of the main study sample: fourteen qualified nurses were recruited to test the acceptability of the questionnaire and minor syntax and formatting modifications were made subsequently; and thirty-four qualified nurses were recruited to assess the test–retest reliability over a 2-week period.
Ethical approval
The study was approved by the Psychiatry, Nursing & Midwifery Ethics Committee of King's College London, London, UK.
Statistical analyses
All analyses were performed using the statistical software package SPSS for Windows version 17·0. Continuous variables are presented as means and standard deviations and were compared using t tests, while categorical variables are presented as frequencies and percentages and were compared using χ 2 tests.
The intra-class correlation coefficient (ICC) and 95 % confidence interval were used to determine the test–retest reliability of the Likert scales in the questionnaire. Frequency distribution and κ statistics were calculated to assess the agreement between perceived weight status and BMI status. Binary logistic regression (Enter method) analysis was used to evaluate associations between weight status misperception and personal profile variables including gender, age, ethnicity, BMI, perceived weight, education background and health status. The 95 % confidence intervals on the odds ratios for each category (as compared with the reference category) were calculated.
The data did not allow for the further analyses of overestimation and underestimation of weight status because of the relatively small number of over-assessors and under-assessors in the sample.
Results
Test–retest reliability for the measures
The test–retest reliabilities indicated satisfactory stability of the measures (Table 1). Test–retest reliability coefficients for self-reported weight, self-reported height and self-perceived weight status were 0·99, 0·98 and 0·97, respectively. The lowest ICC was 0·67 for the PAI of the GPPAQ.
Table 1 Indices of test–retest reliability for the measures
ICC, intra-class correlation coefficient; PAI, Physical Activity Index; GPPAQ, General Practice Physical Activity Questionnaire.
Sample characteristics
The sample (Table 2) comprised mainly females (90·0 %), 66·5 % were white and their mean age was 31 years. Based on self-reported height and weight, the participants’ mean BMI was 24·1 kg/m2; 20·4 % were classified as overweight with 11·0 % as obese, compared with 24·5 % who perceived themselves to be overweight and 3·3 % who perceived themselves to be obese. Nearly three-quarters of participants reported moderate (19·2 %) or active (52·9 %) exercise levels. Also, almost three-quarters of participants (74·1 %) reported one or more co-morbidities of obesity in their family history. Regarding educational background, 68·0 % of student nurses were enrolled in the general adult nursing programme; most of the qualified nurses had achieved a diploma (40·1 %; which takes 2 years of full-time study) or a bachelor's degree (44·1 %; which takes 3 years of study). In addition, most qualified nurses worked in hospitals (88·5 %) within a variety of clinical specialties, and over half (61·0 %) had more than 5 years of nursing experience.
Table 2 Sample characteristics: student nurses and qualified nurses attending a large university in London, UK, 2010
Dip HE, diploma of higher education; PG Dip, postgraduate diploma.
Total numbers may not add to 762 because not all respondents completed all items.
Compared with the student nurses, the qualified nurses were significantly older (36·3 years v. 25·0 years) and heavier, either by actual weight (BMI) or by perceived weight. More ethnic diversity was observed in the qualified nurses than in the student nurses: 56·3 %, 17·9 % and 25·8 % of the qualified nurses were white, (mixed) Asian and (mixed) black, respectively. Differences between the two sub-samples in physical activity levels and family histories of obesity co-morbidities were not significant. The remaining characteristics were measured only in qualified nurses.
In summary, the characteristics of the convenience sample were broadly similar to those of the population of student and qualified nurses studying or working in London. Both groups comprised predominantly women and were studying or working in adult general nursing specialties. Most students were between 22 and 31 years of age and the qualified nurses were between 32 and 41 years of age. The qualified nurses had been educated to diploma or degree level, most worked in medical or surgical units and a minority within other clinical specialties, and the qualified sample was employed by a range of organizations delivering health care across the city. No claims are made that the sample is representative of nurses studying or employed outside London.
Agreement between perceived weight status and BMI status
A moderate level of agreement( Reference Landis and Koch 23 , Reference Carletta 24 ) between self-perceived weight status and BMI status was indicated by a κ of 0·424 in qualified nurses and 0·493 in student nurses (Table 3).
Table 3 Percentage agreement between perceived weight status and BMI status among student nurses and qualified nurses attending a large university in London, UK, 2010
Of all the participants, 71·9 % (n 470) classified themselves correctly, with 8·1 % (n 53) overestimating and 20·0 % (n 131) underestimating their weight status. Of those nurses who were underweight by BMI, 45·9 % (n 17) correctly identified their weight category, while more than half (54·1 %, n 20) overrated their weight status. Of those in the normal weight category by BMI, most (87·1 %, n 358) correctly perceived their weight status. Of those in the overweight category by BMI, 42·1 % (n 77) identified themselves as normal weight; and of those in the obese category by BMI, less than a quarter (24·7 %, n 18) accurately evaluated their weight status. Within the same BMI category, a higher proportion of student nurses classified themselves correctly than qualified nurses, but no significant difference was found between the two samples (76·7 % v. 67·5 %, P > 0·05). When the data were dichotomized into ‘overweight’ and ‘non-overweight’, 31·5 % (n 206) of respondents had a BMI that placed them in the overweight range, of whom 69·4 % (n 143) perceived themselves as overweight.
Predictors for misperceptions of weight status
Initial significant variables were identified by the bivariate analyses (Table 4). Gender, age, ethnicity, BMI status and perceived weight status were significantly associated with misperceptions of weight status in both sub-samples (Table 4). Specifically, misperceivers were more frequently found among men, individuals aged ≥42 years, those who had BMI ≥ 25·0 kg/m2 or perceived themselves as overweight, and among black and mixed black participants. Relevant family histories, physical activity levels and education profile were not related to misperceptions of weight status in both sub-samples; no relationship was observed between misperception and the other variables measured only in the qualified nurse sample.
Table 4 Variables correlated to weight status misperception in student nurses and qualified nurses attending a large university in London, UK, 2010
Dip HE, Diploma of higher education; PG Dip, postgraduate diploma.
In logistic regression allowing for all covariates (Table 5), (mixed) black ethnicity (OR = 2·53, 95 % CI 1·01, 6·32), overweight by BMI (OR = 3·10, 95 % CI 1·31, 7·33) and ≥3 family histories of obesity co-morbidities (OR = 2·51, 95 % CI 1·04, 6·08) were significantly associated with misperceptions at significant levels of P < 0·05 in the sub-sample of student nurses, whereas overweight by BMI (OR = 5·32, 95 % CI 2·66, 10·67) was identified as the only significant variable in the sub-sample of qualified nurses. We did not find weight status misperceptions to be associated with perceived weight status in either of the two sub-samples. Neither gender nor age was associated with weight status misperceptions in either sub-sample.
Table 5 Predictors of weight status misperceptions through logistic regression modelling (Enter method) in student nurses and qualified nurses attending a large university in London, UK, 2010
Ref., referent category.
Discussion
The present study investigated the agreement between self-perceived weight and BMI based on self-reported weight and height in a sample of predominantly female, white nurses attending a London university in the UK. Overall, about one in four student nurses and one in three qualified nurses misperceived their own weight status, in that there was a substantial discrepancy between their self-perceived weight status and their BMI status based upon self-reported weight and height. Moreover, weight status misperception resulted mainly from underestimating their body weight. Most obese nurses did not distinguish between being overweight or obese, while most underweight nurses inappropriately classified themselves as of normal weight.
When compared with the data from the three studies of weight status misperception in health professionals( Reference Perrin, Flower and Ammerman 18 – Reference Kirk, Cockbain and Beazley 20 ), the percentage of correct classification (67·5 %) was higher in our sample of qualified nurses than in those surveyed in Tonga (45·5 %)( Reference Kirk, Cockbain and Beazley 20 ). Within the overweight and obese categories, 69·3 % of our respondents correctly identified their weight status; higher than a sample of overweight US paediatricians (51 %)( Reference Perrin, Flower and Ammerman 18 ), but lower than a sample of overweight Mexican physicians (76 %)( Reference Jiménez-Cruz and Bacardí-Gascón 19 ).
Overall the correct rate of perceived weight status by our student and qualified nurses appeared no better than that in the lay population. Among all BMI categories, 73·6 % and 71·0 % of participants accurately classified their own weight status according to the NHANES 1999–2006( Reference Dorsey, Eberhardt and Ogden 10 ) and the 1991 NHIS( Reference Chang and Christakis 1 ), respectively. This is consistent with 72·5 % of women and 70·2 % of men in the NHANES study( Reference Chang and Christakis 2 ). Among the overweight and obese categories, two representative surveys in the UK in 1999 and 2007( Reference Johnson, Cooke and Croker 8 ) found that 81 % and 75 % of overweight participants (BMI ≥ 25·0 kg/m2) correctly identified their weight status.
The different prevalence of weight status misperception described by these studies may be explained by diversity in sample characteristics, such as age, gender, race/ethnicity and personal weight levels, which are known to influence self-perceived weight appropriateness. Another probable reason was the use of different weight descriptors and the number of categories listed by these studies. Differences between the findings of our study and previous studies may be explained, in part, by differences in methodology across studies. Our participants were asked to select from four weight status categories (thin, normal, overweight, obese) as opposed to the three categories used by the NHANES studies (overweight, about right, underweight)( Reference Chang and Christakis 2 , Reference Johnson-Taylor, Fisher and Hubbard 7 , Reference Dorsey, Eberhardt and Ogden 10 , Reference Yaemsiri, Slining and Agarwal 11 ) and the three categories used by a study of US paediatricians (thin, average, overweight)( Reference Perrin, Flower and Ammerman 18 ). We chose four categories to see if nurses were able to distinguish between overweight and obese categories. Additionally, the ‘normalizing’ of overweight in relation to an increasing prevalence of overweight or obesity over time may account for fewer overweight and obese individuals identifying themselves as overweight( Reference Chang and Christakis 2 , Reference Johnson-Taylor, Fisher and Hubbard 7 , Reference Johnson, Cooke and Croker 8 , Reference Dorsey, Eberhardt and Ogden 10 , Reference Yaemsiri, Slining and Agarwal 11 , Reference Burke, Heiland and Nadler 25 ). Desired weight has also increased over time in the USA( Reference Maynard, Serdula and Galuska 26 ), and nurses’ underestimation of their body weight, which accounted for a large proportion of misperception in the present study, may reflect an upward trend in weight status misperception. Other potential reasons for the high percentage of misclassification among health professionals could be the desire to appear as role models, which may make either doctors or nurses reluctant to label themselves as overweight or obese.
Independent variables associated with weight status misperception
The findings from the present study further suggest that nurses’ misperception of weight status varies by gender, age, race/ethnicity, BMI status and perceived weight status, which is consistent with findings of studies of lay public samples( Reference Bennett and Wolin 3 , Reference Yannakoulia, Panagiotakos and Pitsavos 4 , Reference Dorsey, Eberhardt and Ogden 10 , Reference Paeratakul, White and Williamson 13 ). In both the qualified and student nurses, those who were male, (mixed) black, older than average age, with a BMI ≥ 25·0 kg/m2 or self-perceived overweight were more likely to misperceive their weight status. Of all covariates examined, race/ethnicity, BMI and obesity-related family histories independently influenced the odds of misperceptions of weight status among nurses. In contrast, a study of a sample of 355 US paediatricians found that only gender and BMI were independent predictors for misclassification of overweight status( Reference Perrin, Flower and Ammerman 18 ).
There were some differences in predictors for misperceptions of weight status between the student and qualified nurse sub-samples. Among student nurses, the (mixed) blacks were more likely to misperceive their weight status than whites, as were those with three or more family histories of obesity co-morbidities relative to those without any related family history. In contrast, race/ethnicity and family histories did not independently predict misperceptions of weight status among qualified nurses. It is worth noting that BMI status was the most important predictor in the two sub-samples; that is, both student nurses and qualified nurses with BMI ≥25·0 kg/m2 had more frequent misperception of their own weight status.
Ours is the first known study to evaluate the relationship between weight status misperception and family histories of obesity co-morbidities, with an interesting finding that student nurses with three or more family histories of obesity co-morbidities were more likely to misperceive their weight status than their counterparts without any family history. The reason for this is unclear but one possible explanation is that when family histories of obesity co-morbidities are present, fear of being labelled ‘obesity prone’ or ‘unhealthy’ may increase the motivation to deny being overweight.
No associations were found between weight status misperception and personal physical activity levels, education and work experiences. Regarding personal physical activity levels, the findings of our study contrast those of Miller et al.( Reference Miller, Schulz and Bibeau 27 ) that active overweight individuals may be more likely to incorrectly perceive themselves as being of normal weight. As for education variables (nurse programme or highest educational qualification), our findings differ from previous studies of the lay population( Reference Chang and Christakis 1 , Reference Dorsey, Eberhardt and Ogden 10 ), which have revealed that education has a significant independent effect on the misperception of weight status. All work experience variables (specialty, work places and years in practice) were not associated with weight status misperceptions, in line with a study of paediatricians by Perrin et al.( Reference Perrin, Flower and Ammerman 18 ). This is unsurprising since identification of body weight should be one of the basic skills of nurses, irrespective of their educational level and work experiences.
Prevalence of overweight and obesity among the nurses investigated
Finally, 22·0 % of the student nurses and 39·8 % of the qualified nurses surveyed were overweight or obese, which is less than the UK population's average of 42·7 % in 1999 and 52·9 % in 2007( Reference Johnson, Cooke and Croker 8 , 28 , 29 ). It is also substantially less than the 65 % of men and levels in other health professional groups. For example, a survey of eleven European national colleges (n 2082) found that 31·76 % of general practitioners were overweight and 7·13 % were obese( Reference Brotons, Bjorkelund and Bulc 30 ); similarly, Perrin et al. that found 40 % of paediatricians were overweight( Reference Perrin, Flower and Ammerman 18 ).
Strengths and limitations
The present study is the first known to examine nurses’ misperceptions of weight status associated with sociodemographic characteristics and health status and to compare findings for student nurses and qualified nurses. Our sample size is close to that of a study of US paediatricians by Perrin et al.( Reference Perrin, Flower and Ammerman 18 ) and is the largest among the relevant studies of qualified nurses or university students studying health-related courses( Reference Jaworowska and Bazylak 15 , Reference Kirk, Cockbain and Beazley 20 , Reference Requejo, Ortega and Quintas 31 – Reference Malinauskas, Raedeke and Aeby 33 ). Moreover, in addition to frequently investigated sociodemographic variables, our study is the first to investigate the influence of family histories of obesity co-morbidities on the misperception of weight status.
Our cross-sectional study has several limitations. A limitation is the use of a convenience sample from a single university, which may have introduced bias through selective recruitment of nurses with particular views and interest in the subject. In addition, the sample included a very small subgroup of males, those of older age and non-white race, which limits detection of differences in weight misperception by gender, age and race/ethnicity and also means that the findings of the study should not be generalized. A further limitation is possible biases from missing responses. Missing value analysis demonstrated that the data were not missing completely at random. Female, self-perceived overweight and non-white race were variables that were closely related to missing responses, which might result in an underestimate of the impact of demographic factors on the misclassification of weight status. Like many studies, our study is also limited by calculation of BMI from self-reported weight and height, variables which have been demonstrated to be under- and over-reported respectively in previous studies( Reference Stewart, Jackson and Ford 34 , Reference Nieto-García, Bush and Keyl 35 ) although a satisfactory test–retest reliability of the measures was confirmed in our study.
Conclusions
The present study is limited by its sample which was drawn from a single London university, the great majority of whom were female and white. While the study findings cannot be generalized, it contributes to the growing literature on the discrepancy between self-perceived weight and actual weight and highlights the need for further research, particularly in view of the increasingly important role played in health promotion by nurses and other health professionals in relation to obesity prevention.
We observed a substantial discrepancy between BMI and self-perceived weight status in both student and qualified nurses, particularly among the (mixed) blacks, the overweight (BMI ≥ 25·0 kg/m2) and those with three or more three family histories of obesity co-morbidities. Further research is needed to identify variables associated with underestimating or overestimating weight status among nurses and to further explore the impact of such misperceptions on nurses’ approach to weight problems in practice; for instance, whether nurses’ misperception of their own body weight is associated with their identification of overweight patients.
Acknowledgements
Sources of funding: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Conflicts of interest: The authors have no conflicts of interest. Authors’ contributions: D.Q.Z. contributed to the design of the study, drafted the questionnaire, developed the questionnaire, collected and analysed the data, and drafted and approved the submitted manuscript. I.J.N. and A.E.W. contributed to the design of the study, revised the questionnaire, contributed to data collection and analysis, critically revised the manuscript and approved the submitted manuscript. Acknowledgements: The authors thank the qualified and student nurses who participated in the study.
