Example: Symptomatology of Eating Disorders
Eating disorders are debilitating illnesses associated with disturbances in eating behavior, severe body image distortion, and an obsession with weight that affects the mind and body simultaneously. Millions of people are affected each year, with adolescents particularly at risk. Treatments are available and most are helpful when the condition is identified early.
A health professional can attempt to diagnose an eating disorder through a psychological and medical evaluation. However, it can be difficult to assign a patient to one of several different classes of eating disorders because there is no standardized symptomatology of anorectic/bulimic behavior. Are there symptoms that clearly differentiate patients into the four groups? Which symptoms do they have in common?
In order to try to answer these questions, researchers 1 made a study of 55 adolescents with known eating disorders, as shown in the following table.
| Diagnosis | Number of Patients |
|---|---|
| Anorexia nervosa | 25 |
| Anorexia with bulimia nervosa | 9 |
| Bulimia nervosa after anorexia | 14 |
| Atypical eating disorder | 7 |
| Total | 55 |
Each patient was seen four times over four years, for a total of 220 observations. At each observation, the patients were scored for each of the 16 symptoms outlined in the following table. Symptom scores are missing for patient 71 at time 2, patient 76 at time 2, and patient 47 at time 3, leaving 217 valid observations. The data can be found in anorectic.sav.See the topic Sample Files for more information.
| Variable name | Variable label | Lower end (score1) | Upper end (score 3 or 4) |
|---|---|---|---|
| weight | Body weight | Outside normal range | Normal |
| mens | Menstruation | Amenorrhea | Regular periods |
| fast | Restriction of food intake (fasting) | Less than 1200 calories | Normal/regular meals |
| binge | Binge eating | Greater than once a week | No bingeing |
| vomit | Vomiting | Greater than once a week | No vomiting |
| purge | Purging | Greater than once a week | No purging |
| hyper | Hyperactivity | Not able to be at rest | No hyperactivity |
| fami | Family relations | Poor | Good |
| eman | Emancipation from family | Very dependent | Adequate |
| frie | Friends | No good friends | Two or more good friends |
| school | School/employment record | Stopped school/work | Moderate to good record |
| satt | Sexual attitude | Inadequate | Adequate |
| sbeh | Sexual behavior | Inadequate | Can enjoy sex |
| mood | Mental state (mood) | Very depressed | Normal |
| preo | Preoccupation with food and weight | Complete | No preoccupation |
| body | Body perception | Disturbed | Normal |
Principal components analysis is ideal for this situation, since the purpose of the study is to ascertain the relationships between symptoms and the different classes of eating disorders. Moreover, categorical principal components analysis is likely to be more useful than classical principal components analysis because the symptoms are scored on an ordinal scale.