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Cluster analysis: Classification of color vision test results from the ETDRS and other possible applications
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Abstracts Trial including weight, urinary electrolyte excretion, and electrolyte intake as determined from daily food records.
On the Power of Two Tests for Qualitative Interaction S t e v e n Piantadosi a n d Mitchell Gall
National Cancer Institute, Bethesda, Maryland (08) It is of clinical importance to know when a new treatment is superior compared to control in some subsets of patients and inferior in others. Such a change in sign of the treatment effect is called a "qualitative interaction." Gall and Simon (Biometrics 41,361-372 1985) proposed a likelihood ratio test for detecting such interactions. The present work proposes an alternative test for qualitative interactions and presents results on the power of these two tests. Our results emphasize the need for large samples to detect qualitative interactions and suggest alternatives for which one or the other test is preferable. Cluster Analysis: Classification of Color Vision Test Results From the ETDRS and Other Possible Applications Franca Barton
Maryland Medical Research Institute (09) Farnsworth-Munsell 100-Hue Test results for an individual are usually presented in a twodimensional display. This multiple variable information can be used to group cases into classes of frequently observed patterns. Rules for identifying these patterns computationally into groups do not currently exist for color vision results. Multiple variables must be used in developing a classification scheme. Cluster analysis is used on baseline color vision data from the ETDRS to iden~i~ the classes and derive the algorithm to assign a case to its appropriate pattern. The classification scheme resulting from cluster analysis from the entire data set is replicated with selected subsets of test results. This approach can be used for other multidimensional data such as electroencephalogram, x-rays, cardiac function measurements, dietary intake measures, etc. Measuring Electrolyte Excretion From Random Overnight Urine Collections Janet Hiller, Michele D o n i t h a n , J a m e s Tonascia, a n d H e r b e r t L a n g f o r d
Johns Hopkins School of Public Health for the Hypertension Prevention Trial, Baltimore, Maryland (10) Clinical trials in the hypertension area often need to collect timed urine samples to determine changes in electrolyte excretion. The longer the collection time, the more difficult the logistical difficulties. For collections of 24 hours or longer, participants usually select a "convenient" time to make the collection. This paper compares this usual approach with timed overnight urine collections made on randomly selected days. We collected overnight and rest of 24-hour urines from 120 participants in 4 clinical centers of the Hypertension Prevention Trial. Five alternative statistical methods for predicting the 24-hour excretion from just the overnight excretion are presented. While simple correlation coefficients for the methods did not differ markedly (about 0.88 for sodium, 0.74 for potassium and 0,88 for creatinine), substantial bias in estimating population values may be introduced depending upon which method is employed. The bias was least with the method that predicted the daytime from the overnight portion with a linear regression equation, and then combined the two to make the 24-hour estimate. Our results indicate that the conceptually and logistically appealing measurement of electrolytes via a timed overnight collection is adequate for most clinical trial settings.
Interrater Reliability of SAFTEE In Psychopharmacologic Clinical Trials Alan Frank J a c o b s o n
University of Miami School of Medicine (11) Systematic Assessment for Treatment Emergent Events (SAFTEE) is a newly developed system designed to provide a standardized examination procedure to be used in identifying the occur-
Abstracts Trial including weight, urinary electrolyte excretion, and electrolyte intake as determined from daily food records.
On the Power of Two Tests for Qualitative Interaction S t e v e n Piantadosi a n d Mitchell Gall
National Cancer Institute, Bethesda, Maryland (08) It is of clinical importance to know when a new treatment is superior compared to control in some subsets of patients and inferior in others. Such a change in sign of the treatment effect is called a "qualitative interaction." Gall and Simon (Biometrics 41,361-372 1985) proposed a likelihood ratio test for detecting such interactions. The present work proposes an alternative test for qualitative interactions and presents results on the power of these two tests. Our results emphasize the need for large samples to detect qualitative interactions and suggest alternatives for which one or the other test is preferable. Cluster Analysis: Classification of Color Vision Test Results From the ETDRS and Other Possible Applications Franca Barton
Maryland Medical Research Institute (09) Farnsworth-Munsell 100-Hue Test results for an individual are usually presented in a twodimensional display. This multiple variable information can be used to group cases into classes of frequently observed patterns. Rules for identifying these patterns computationally into groups do not currently exist for color vision results. Multiple variables must be used in developing a classification scheme. Cluster analysis is used on baseline color vision data from the ETDRS to iden~i~ the classes and derive the algorithm to assign a case to its appropriate pattern. The classification scheme resulting from cluster analysis from the entire data set is replicated with selected subsets of test results. This approach can be used for other multidimensional data such as electroencephalogram, x-rays, cardiac function measurements, dietary intake measures, etc. Measuring Electrolyte Excretion From Random Overnight Urine Collections Janet Hiller, Michele D o n i t h a n , J a m e s Tonascia, a n d H e r b e r t L a n g f o r d
Johns Hopkins School of Public Health for the Hypertension Prevention Trial, Baltimore, Maryland (10) Clinical trials in the hypertension area often need to collect timed urine samples to determine changes in electrolyte excretion. The longer the collection time, the more difficult the logistical difficulties. For collections of 24 hours or longer, participants usually select a "convenient" time to make the collection. This paper compares this usual approach with timed overnight urine collections made on randomly selected days. We collected overnight and rest of 24-hour urines from 120 participants in 4 clinical centers of the Hypertension Prevention Trial. Five alternative statistical methods for predicting the 24-hour excretion from just the overnight excretion are presented. While simple correlation coefficients for the methods did not differ markedly (about 0.88 for sodium, 0.74 for potassium and 0,88 for creatinine), substantial bias in estimating population values may be introduced depending upon which method is employed. The bias was least with the method that predicted the daytime from the overnight portion with a linear regression equation, and then combined the two to make the 24-hour estimate. Our results indicate that the conceptually and logistically appealing measurement of electrolytes via a timed overnight collection is adequate for most clinical trial settings.
Interrater Reliability of SAFTEE In Psychopharmacologic Clinical Trials Alan Frank J a c o b s o n
University of Miami School of Medicine (11) Systematic Assessment for Treatment Emergent Events (SAFTEE) is a newly developed system designed to provide a standardized examination procedure to be used in identifying the occur-