Tympanometry Interpretation by Primary Care Physicians

Tympanometry has been assessed and is sometimes promoted as a useful tool in the management of children with ear infections and effusions.^1-6 Recently a group at the Centers for Disease Control and Prevention⁷ recommended tympanometry as a procedure of value when the diagnosis of acute otitis media is uncertain. It provides an objective assessment of the status of the middle ear^8-10 and for some children correlates with hearing loss.^11-12 The feasibility of using hand-held tympanometers in family practice has been established,^3-13 but the accuracy of the interpretations of tympanograms made by primary care physicians is unknown.¹⁴ We report the level of agreement of interpretations of tympanograms between practicing primary care physicians and experts.

Methods

As part of a study of acute otitis media, 131 primary care physicians obtained 6358 tympanograms from 1773 children aged 6 to 180 months during 3179 routine practice visits: 2236 in the Netherlands, 1594 in the United Kingdom, and 2528 in North America. Data from Canada and the United States were combined, because the practices were united in one network (The Ambulatory Sentinel Practice Network), and followed the same study standards. Visits occurred either at the time of the diagnosis of a new episode of acute otitis media, or at 2- or 5-month study follow-up visits. Diagnostic criteria for acute otitis media included either otoscopic evidence of a bulging tympanic membrane, drainage of pus, or a red ear accompanied by ear pain.

A study coordinator trained each physician in the otoscopic examination of the ear, the use of the Welch Allyn Micro Tymp 2 (Skaneateles Falls, NY), and tympanogram interpretation. The study physicians were observed and coached as necessary until they were able to demonstrate competence to the study coordinator. The physicians were provided with a calibrated tympanometer and printer. The Modified Jerger Classification¹ which includes 5 categories (A, C1, C2, B, and uninterpretable) was used. This established classification is based primarily on the pressure at which acoustic admittance is greatest (A: -99 to 200 daPa; C1: -199 to -100 daPa; C2: -399 to -200 daPa; B: less than -399, seen as a flat tracing)

Tympanograms were forwarded to national data centers and blindly reinterpreted by 1 of 3 national study coordinators. The study coordinators identified difficult to interpret tympanograms, reached agreement about rules to be used in their interpretation, and informed the participating physicians of these rules during the ongoing study. These national coordinators and the criterion referee interpreted a set of 52 tympanograms randomly selected from a pool of difficult to interpret tympanograms. The k statistic, a chance-corrected measure of agreement, was calculated using SPSS software (Chicago, Ill) to determine inter-rater agreement.¹⁵ A k of 0.75 or greater represents excellent agreement beyond chance, and values between 0.40 and 0.75 represent fair to good agreement. Kappas for expert interrater reliability ranged from 0.77 to 0.95. Conflicts among the interpretations of the expert national study coordinators were resolved by the most experienced investigator, who served as the study’s criterion standard.¹³

Data from the interpretations of the tympanograms were organized by country (Canada and the United States were combined as North America), age of child (6-12,13-24, and 25-180 months),¹⁶ and type of visit (initial, follow-up at 2 months, follow-up at 5 months). On the basis of established cut-points related to sensitivity and specificity, C1 and A interpretations were categorized as normal and C2 and B as abnormal. The interpretation of individual tympanograms is important in determining test performance. However, treatment decisions affect the whole child and depend on assessment of the combined interpretation of tympanograms from both ears obtained from a child during a visit. Therefore, both individual and bilateral sets of tympanograms obtained for a child at a visit were used as units of analyses.

Significance testing of differences is not reported because of small standard deviations associated with most of the observations.

Results

The expert national coordinators interpreted 35.8% of the tympanograms as A curves, 30% as B curves, 15.5% as C1 curves, and 12% as C2 curves. Only 6.8% of the curves were considered uninterpretable, ranging from a high of 9.5% at initial visits to a low of 3.0% at 5-month visits. The distribution of the interpretations by country, age group, and visit type is shown in Table 1.

From a clinical perspective decisions are made on the basis of individuals, not ears. As shown in Table 2, 37.8% of the visiting children were classified as normal (A or C1 classification of both ears), 55.6% as abnormal (B or C2 classification of at least one ear), and 6.6% could not be classified. The distribution varied by country, age, and type of visit. The Netherlands had the largest percentage of children with abnormal tympanograms. A majority of children had an abnormal tympanogram at the initial visit, but there was little difference among children in the 3 age groups.

There was a high level of agreement between primary care physicians and the experts as shown in Table 3. Agreement in interpretation of the tympanograms in both type of curve (A, C1, C2, B) and classification of children as normal or abnormal was high in all countries, in all the age groups, and at all types of visits. Similarly, agreement was high in all countries, age groups, and visit types for classification of children at visits as normal or abnormal on the basis of tympanograms of both ears, with the lowest k (0.58) for children at their initial visits, and kappas of 0.76 and 0.75 at follow-up visits.

Discussion

The need for primary care research in practice settings is established.¹⁷ Some researchers, however, question the accuracy of the data gathered and reported by busy primary care clinicians in their practice settings. Our findings demonstrate that primary care physicians can obtain and accurately interpret tympanograms during daily practice. A high level of agreement with experts was found in the Netherlands, the United Kingdom, and North America for infants and older children and at initial as well as follow-up visits for children with acute otitis media. High levels of agreement persisted when analyzed as bilateral sets of tympanograms obtained at a visit. This analysis suggests agreement at the level most relevant to clinical decision making in primary care.

The lower—but still high—level of agreement in interpretations by child at initial visit may relate to physiological, anatomic, and behavioral aspects present at the early stages of acute otitis media as seen in the primary care setting. The higher levels of agreement at follow-up are reassuring, given the role of tympanometry in assessing effusion as a potential complication of acute otitis media.

Conclusions

The results of our study are unique and important because they are robust and based on large numbers of tympanograms obtained from both infants and older children in primary care practices in the Netherlands, the United Kingdom, the United States, and Canada. Our findings support the assertion that primary care physicians can successfully use tympanometry but offer no data to verify the relevance of tympanometry in the management of acute otitis media or other middle ear disease in primary care. Tympanometry is feasible in primary care practice, and the results obtained by physicians trained in the use of the Modified Jerger Classification can be used with confidence. These results provide further evidence that practicing primary care physicians can provide high-quality data for research purposes.

Acknowledgments

Our work was supported by the Agency for Health Care Policy and Research grant no. RO1 HS07035-03. The tympanometers were purchased at a discounted rate from Welch Allyn. The participating physicians were: Ambulatory Sentinel Practice Network (United States and Canada): Arlis Adolf, Jules Amer, John Anderson, Robert Baker, Gordon Blakeman, Brian Caplan, Paul Collins, Bill Davis, Richard Douglass, Patricia Fibiger, Stephen Fischer, Ed Friedler, Ronald Gagne, Thomas Gilbert, Susan Girardeau, John Glennon, Gary Gray, Cindy Hansen, Terry Hankey, Michael Hartsell, Joseph Hildner, Robert Howse, Jr., Robert James, Roger Kimber, Gary Knaus, Paula Leonard-Schwartz, Mary Maguire, Kim Manning, Kathleen McGarr, Doreen McMahon, Jasmine Moghissi, Michael Mulligan, William Nietert, Spiro Papadopoulos, Donya Powers, Thomas Overholt, Steve Perry, Paul Schmitt, John Scott, Susan Shapiro, Brian Siray, Kimball Spence, Jon Sternburg, Linda Stewart, Lynne Studebaker, James Wickerath, Elizabeth Wise, and Lloyd Wollstadt. Surrey GP Network (the United Kingdom): Nick Barrie, G. Bennett, S. Brown, Jace Clarke, Mark Cornbloom, I. Davies, Niall Ferguson, N. Fisher, Richard France, Paul Grob, Mark Hanan, Robert Harvey, John Healey, David William Holwell, R. N. Jeffery, Murdo Macleod, Mather, Philip Moore, Julia Oxenbury, Margaret Palmer, C. A. Pearson, C. Pidgeon, M. Pujara, David Skipp, A. Smith, K. Tarrant, Chris Tibbott, Brett J. Whitby-Smith, Hamish Whitaker, Mary Anne Whitehead, P. R. Wilks, Sidney Worthington, and J. Young. University of Utrecht Network (the Netherlands): Atyvan Aarnhem, G. Ploosvan Amstel, D. B. van Baarda, Marja Baeten, P. J. van Beek, H. C. V. Berkum, R. Bohm, J. C. M. van Campen, J. W. Cirkel, H. J. R. Dorman, J. H. Duistermaat, H. van Es, N. Goudswaard, N. de Grunt, Ax. M. E. J. Hoeberichts, M. E. van der Hoek, J. M. P. M. Janssen, E. G. A. de Jong, L. Klaphake, A. W. K. Kramer, J. Kuiper, N. Kwakernaak, Hans Kootte, Jaap R. van der Laan, O. J. M. Lackamp, C. G. Lameris, Marjan Lamers, H. C. de Lathouder, P. J. Luyendijk, G. A. M. Maathuis, R. H. L. Morshuis, W. P. G. Mulder, P. L. W. Pijman, F. G. Pingen, Pricleer, Liesbeth Redeke, M. J. G. van Roosmalen, C. J. Rovers, S. H. A. Schmeets, J. F. Scholte, B. P. Schreuder, T. Steenkamer, Jette Timmer-Martijn, F. Trip, de Vries, Christine Weenink, H. C. P. M. van Weert, P. Willems, Boes Willemse, and P. van de Woestijne.

Tympanometry has been assessed and is sometimes promoted as a useful tool in the management of children with ear infections and effusions.^1-6 Recently a group at the Centers for Disease Control and Prevention⁷ recommended tympanometry as a procedure of value when the diagnosis of acute otitis media is uncertain. It provides an objective assessment of the status of the middle ear^8-10 and for some children correlates with hearing loss.^11-12 The feasibility of using hand-held tympanometers in family practice has been established,^3-13 but the accuracy of the interpretations of tympanograms made by primary care physicians is unknown.¹⁴ We report the level of agreement of interpretations of tympanograms between practicing primary care physicians and experts.

Methods

As part of a study of acute otitis media, 131 primary care physicians obtained 6358 tympanograms from 1773 children aged 6 to 180 months during 3179 routine practice visits: 2236 in the Netherlands, 1594 in the United Kingdom, and 2528 in North America. Data from Canada and the United States were combined, because the practices were united in one network (The Ambulatory Sentinel Practice Network), and followed the same study standards. Visits occurred either at the time of the diagnosis of a new episode of acute otitis media, or at 2- or 5-month study follow-up visits. Diagnostic criteria for acute otitis media included either otoscopic evidence of a bulging tympanic membrane, drainage of pus, or a red ear accompanied by ear pain.

A study coordinator trained each physician in the otoscopic examination of the ear, the use of the Welch Allyn Micro Tymp 2 (Skaneateles Falls, NY), and tympanogram interpretation. The study physicians were observed and coached as necessary until they were able to demonstrate competence to the study coordinator. The physicians were provided with a calibrated tympanometer and printer. The Modified Jerger Classification¹ which includes 5 categories (A, C1, C2, B, and uninterpretable) was used. This established classification is based primarily on the pressure at which acoustic admittance is greatest (A: -99 to 200 daPa; C1: -199 to -100 daPa; C2: -399 to -200 daPa; B: less than -399, seen as a flat tracing)

Tympanograms were forwarded to national data centers and blindly reinterpreted by 1 of 3 national study coordinators. The study coordinators identified difficult to interpret tympanograms, reached agreement about rules to be used in their interpretation, and informed the participating physicians of these rules during the ongoing study. These national coordinators and the criterion referee interpreted a set of 52 tympanograms randomly selected from a pool of difficult to interpret tympanograms. The k statistic, a chance-corrected measure of agreement, was calculated using SPSS software (Chicago, Ill) to determine inter-rater agreement.¹⁵ A k of 0.75 or greater represents excellent agreement beyond chance, and values between 0.40 and 0.75 represent fair to good agreement. Kappas for expert interrater reliability ranged from 0.77 to 0.95. Conflicts among the interpretations of the expert national study coordinators were resolved by the most experienced investigator, who served as the study’s criterion standard.¹³

Data from the interpretations of the tympanograms were organized by country (Canada and the United States were combined as North America), age of child (6-12,13-24, and 25-180 months),¹⁶ and type of visit (initial, follow-up at 2 months, follow-up at 5 months). On the basis of established cut-points related to sensitivity and specificity, C1 and A interpretations were categorized as normal and C2 and B as abnormal. The interpretation of individual tympanograms is important in determining test performance. However, treatment decisions affect the whole child and depend on assessment of the combined interpretation of tympanograms from both ears obtained from a child during a visit. Therefore, both individual and bilateral sets of tympanograms obtained for a child at a visit were used as units of analyses.

Significance testing of differences is not reported because of small standard deviations associated with most of the observations.

Results

The expert national coordinators interpreted 35.8% of the tympanograms as A curves, 30% as B curves, 15.5% as C1 curves, and 12% as C2 curves. Only 6.8% of the curves were considered uninterpretable, ranging from a high of 9.5% at initial visits to a low of 3.0% at 5-month visits. The distribution of the interpretations by country, age group, and visit type is shown in Table 1.

From a clinical perspective decisions are made on the basis of individuals, not ears. As shown in Table 2, 37.8% of the visiting children were classified as normal (A or C1 classification of both ears), 55.6% as abnormal (B or C2 classification of at least one ear), and 6.6% could not be classified. The distribution varied by country, age, and type of visit. The Netherlands had the largest percentage of children with abnormal tympanograms. A majority of children had an abnormal tympanogram at the initial visit, but there was little difference among children in the 3 age groups.

There was a high level of agreement between primary care physicians and the experts as shown in Table 3. Agreement in interpretation of the tympanograms in both type of curve (A, C1, C2, B) and classification of children as normal or abnormal was high in all countries, in all the age groups, and at all types of visits. Similarly, agreement was high in all countries, age groups, and visit types for classification of children at visits as normal or abnormal on the basis of tympanograms of both ears, with the lowest k (0.58) for children at their initial visits, and kappas of 0.76 and 0.75 at follow-up visits.

Discussion

The need for primary care research in practice settings is established.¹⁷ Some researchers, however, question the accuracy of the data gathered and reported by busy primary care clinicians in their practice settings. Our findings demonstrate that primary care physicians can obtain and accurately interpret tympanograms during daily practice. A high level of agreement with experts was found in the Netherlands, the United Kingdom, and North America for infants and older children and at initial as well as follow-up visits for children with acute otitis media. High levels of agreement persisted when analyzed as bilateral sets of tympanograms obtained at a visit. This analysis suggests agreement at the level most relevant to clinical decision making in primary care.

The lower—but still high—level of agreement in interpretations by child at initial visit may relate to physiological, anatomic, and behavioral aspects present at the early stages of acute otitis media as seen in the primary care setting. The higher levels of agreement at follow-up are reassuring, given the role of tympanometry in assessing effusion as a potential complication of acute otitis media.

Conclusions

The results of our study are unique and important because they are robust and based on large numbers of tympanograms obtained from both infants and older children in primary care practices in the Netherlands, the United Kingdom, the United States, and Canada. Our findings support the assertion that primary care physicians can successfully use tympanometry but offer no data to verify the relevance of tympanometry in the management of acute otitis media or other middle ear disease in primary care. Tympanometry is feasible in primary care practice, and the results obtained by physicians trained in the use of the Modified Jerger Classification can be used with confidence. These results provide further evidence that practicing primary care physicians can provide high-quality data for research purposes.

Acknowledgments

Our work was supported by the Agency for Health Care Policy and Research grant no. RO1 HS07035-03. The tympanometers were purchased at a discounted rate from Welch Allyn. The participating physicians were: Ambulatory Sentinel Practice Network (United States and Canada): Arlis Adolf, Jules Amer, John Anderson, Robert Baker, Gordon Blakeman, Brian Caplan, Paul Collins, Bill Davis, Richard Douglass, Patricia Fibiger, Stephen Fischer, Ed Friedler, Ronald Gagne, Thomas Gilbert, Susan Girardeau, John Glennon, Gary Gray, Cindy Hansen, Terry Hankey, Michael Hartsell, Joseph Hildner, Robert Howse, Jr., Robert James, Roger Kimber, Gary Knaus, Paula Leonard-Schwartz, Mary Maguire, Kim Manning, Kathleen McGarr, Doreen McMahon, Jasmine Moghissi, Michael Mulligan, William Nietert, Spiro Papadopoulos, Donya Powers, Thomas Overholt, Steve Perry, Paul Schmitt, John Scott, Susan Shapiro, Brian Siray, Kimball Spence, Jon Sternburg, Linda Stewart, Lynne Studebaker, James Wickerath, Elizabeth Wise, and Lloyd Wollstadt. Surrey GP Network (the United Kingdom): Nick Barrie, G. Bennett, S. Brown, Jace Clarke, Mark Cornbloom, I. Davies, Niall Ferguson, N. Fisher, Richard France, Paul Grob, Mark Hanan, Robert Harvey, John Healey, David William Holwell, R. N. Jeffery, Murdo Macleod, Mather, Philip Moore, Julia Oxenbury, Margaret Palmer, C. A. Pearson, C. Pidgeon, M. Pujara, David Skipp, A. Smith, K. Tarrant, Chris Tibbott, Brett J. Whitby-Smith, Hamish Whitaker, Mary Anne Whitehead, P. R. Wilks, Sidney Worthington, and J. Young. University of Utrecht Network (the Netherlands): Atyvan Aarnhem, G. Ploosvan Amstel, D. B. van Baarda, Marja Baeten, P. J. van Beek, H. C. V. Berkum, R. Bohm, J. C. M. van Campen, J. W. Cirkel, H. J. R. Dorman, J. H. Duistermaat, H. van Es, N. Goudswaard, N. de Grunt, Ax. M. E. J. Hoeberichts, M. E. van der Hoek, J. M. P. M. Janssen, E. G. A. de Jong, L. Klaphake, A. W. K. Kramer, J. Kuiper, N. Kwakernaak, Hans Kootte, Jaap R. van der Laan, O. J. M. Lackamp, C. G. Lameris, Marjan Lamers, H. C. de Lathouder, P. J. Luyendijk, G. A. M. Maathuis, R. H. L. Morshuis, W. P. G. Mulder, P. L. W. Pijman, F. G. Pingen, Pricleer, Liesbeth Redeke, M. J. G. van Roosmalen, C. J. Rovers, S. H. A. Schmeets, J. F. Scholte, B. P. Schreuder, T. Steenkamer, Jette Timmer-Martijn, F. Trip, de Vries, Christine Weenink, H. C. P. M. van Weert, P. Willems, Boes Willemse, and P. van de Woestijne.

Tympanometry has been assessed and is sometimes promoted as a useful tool in the management of children with ear infections and effusions.^1-6 Recently a group at the Centers for Disease Control and Prevention⁷ recommended tympanometry as a procedure of value when the diagnosis of acute otitis media is uncertain. It provides an objective assessment of the status of the middle ear^8-10 and for some children correlates with hearing loss.^11-12 The feasibility of using hand-held tympanometers in family practice has been established,^3-13 but the accuracy of the interpretations of tympanograms made by primary care physicians is unknown.¹⁴ We report the level of agreement of interpretations of tympanograms between practicing primary care physicians and experts.

Methods

As part of a study of acute otitis media, 131 primary care physicians obtained 6358 tympanograms from 1773 children aged 6 to 180 months during 3179 routine practice visits: 2236 in the Netherlands, 1594 in the United Kingdom, and 2528 in North America. Data from Canada and the United States were combined, because the practices were united in one network (The Ambulatory Sentinel Practice Network), and followed the same study standards. Visits occurred either at the time of the diagnosis of a new episode of acute otitis media, or at 2- or 5-month study follow-up visits. Diagnostic criteria for acute otitis media included either otoscopic evidence of a bulging tympanic membrane, drainage of pus, or a red ear accompanied by ear pain.

A study coordinator trained each physician in the otoscopic examination of the ear, the use of the Welch Allyn Micro Tymp 2 (Skaneateles Falls, NY), and tympanogram interpretation. The study physicians were observed and coached as necessary until they were able to demonstrate competence to the study coordinator. The physicians were provided with a calibrated tympanometer and printer. The Modified Jerger Classification¹ which includes 5 categories (A, C1, C2, B, and uninterpretable) was used. This established classification is based primarily on the pressure at which acoustic admittance is greatest (A: -99 to 200 daPa; C1: -199 to -100 daPa; C2: -399 to -200 daPa; B: less than -399, seen as a flat tracing)

Tympanograms were forwarded to national data centers and blindly reinterpreted by 1 of 3 national study coordinators. The study coordinators identified difficult to interpret tympanograms, reached agreement about rules to be used in their interpretation, and informed the participating physicians of these rules during the ongoing study. These national coordinators and the criterion referee interpreted a set of 52 tympanograms randomly selected from a pool of difficult to interpret tympanograms. The k statistic, a chance-corrected measure of agreement, was calculated using SPSS software (Chicago, Ill) to determine inter-rater agreement.¹⁵ A k of 0.75 or greater represents excellent agreement beyond chance, and values between 0.40 and 0.75 represent fair to good agreement. Kappas for expert interrater reliability ranged from 0.77 to 0.95. Conflicts among the interpretations of the expert national study coordinators were resolved by the most experienced investigator, who served as the study’s criterion standard.¹³

Data from the interpretations of the tympanograms were organized by country (Canada and the United States were combined as North America), age of child (6-12,13-24, and 25-180 months),¹⁶ and type of visit (initial, follow-up at 2 months, follow-up at 5 months). On the basis of established cut-points related to sensitivity and specificity, C1 and A interpretations were categorized as normal and C2 and B as abnormal. The interpretation of individual tympanograms is important in determining test performance. However, treatment decisions affect the whole child and depend on assessment of the combined interpretation of tympanograms from both ears obtained from a child during a visit. Therefore, both individual and bilateral sets of tympanograms obtained for a child at a visit were used as units of analyses.

Significance testing of differences is not reported because of small standard deviations associated with most of the observations.

Results

The expert national coordinators interpreted 35.8% of the tympanograms as A curves, 30% as B curves, 15.5% as C1 curves, and 12% as C2 curves. Only 6.8% of the curves were considered uninterpretable, ranging from a high of 9.5% at initial visits to a low of 3.0% at 5-month visits. The distribution of the interpretations by country, age group, and visit type is shown in Table 1.

From a clinical perspective decisions are made on the basis of individuals, not ears. As shown in Table 2, 37.8% of the visiting children were classified as normal (A or C1 classification of both ears), 55.6% as abnormal (B or C2 classification of at least one ear), and 6.6% could not be classified. The distribution varied by country, age, and type of visit. The Netherlands had the largest percentage of children with abnormal tympanograms. A majority of children had an abnormal tympanogram at the initial visit, but there was little difference among children in the 3 age groups.

There was a high level of agreement between primary care physicians and the experts as shown in Table 3. Agreement in interpretation of the tympanograms in both type of curve (A, C1, C2, B) and classification of children as normal or abnormal was high in all countries, in all the age groups, and at all types of visits. Similarly, agreement was high in all countries, age groups, and visit types for classification of children at visits as normal or abnormal on the basis of tympanograms of both ears, with the lowest k (0.58) for children at their initial visits, and kappas of 0.76 and 0.75 at follow-up visits.

Discussion

The need for primary care research in practice settings is established.¹⁷ Some researchers, however, question the accuracy of the data gathered and reported by busy primary care clinicians in their practice settings. Our findings demonstrate that primary care physicians can obtain and accurately interpret tympanograms during daily practice. A high level of agreement with experts was found in the Netherlands, the United Kingdom, and North America for infants and older children and at initial as well as follow-up visits for children with acute otitis media. High levels of agreement persisted when analyzed as bilateral sets of tympanograms obtained at a visit. This analysis suggests agreement at the level most relevant to clinical decision making in primary care.

The lower—but still high—level of agreement in interpretations by child at initial visit may relate to physiological, anatomic, and behavioral aspects present at the early stages of acute otitis media as seen in the primary care setting. The higher levels of agreement at follow-up are reassuring, given the role of tympanometry in assessing effusion as a potential complication of acute otitis media.

Conclusions

The results of our study are unique and important because they are robust and based on large numbers of tympanograms obtained from both infants and older children in primary care practices in the Netherlands, the United Kingdom, the United States, and Canada. Our findings support the assertion that primary care physicians can successfully use tympanometry but offer no data to verify the relevance of tympanometry in the management of acute otitis media or other middle ear disease in primary care. Tympanometry is feasible in primary care practice, and the results obtained by physicians trained in the use of the Modified Jerger Classification can be used with confidence. These results provide further evidence that practicing primary care physicians can provide high-quality data for research purposes.

Acknowledgments

Our work was supported by the Agency for Health Care Policy and Research grant no. RO1 HS07035-03. The tympanometers were purchased at a discounted rate from Welch Allyn. The participating physicians were: Ambulatory Sentinel Practice Network (United States and Canada): Arlis Adolf, Jules Amer, John Anderson, Robert Baker, Gordon Blakeman, Brian Caplan, Paul Collins, Bill Davis, Richard Douglass, Patricia Fibiger, Stephen Fischer, Ed Friedler, Ronald Gagne, Thomas Gilbert, Susan Girardeau, John Glennon, Gary Gray, Cindy Hansen, Terry Hankey, Michael Hartsell, Joseph Hildner, Robert Howse, Jr., Robert James, Roger Kimber, Gary Knaus, Paula Leonard-Schwartz, Mary Maguire, Kim Manning, Kathleen McGarr, Doreen McMahon, Jasmine Moghissi, Michael Mulligan, William Nietert, Spiro Papadopoulos, Donya Powers, Thomas Overholt, Steve Perry, Paul Schmitt, John Scott, Susan Shapiro, Brian Siray, Kimball Spence, Jon Sternburg, Linda Stewart, Lynne Studebaker, James Wickerath, Elizabeth Wise, and Lloyd Wollstadt. Surrey GP Network (the United Kingdom): Nick Barrie, G. Bennett, S. Brown, Jace Clarke, Mark Cornbloom, I. Davies, Niall Ferguson, N. Fisher, Richard France, Paul Grob, Mark Hanan, Robert Harvey, John Healey, David William Holwell, R. N. Jeffery, Murdo Macleod, Mather, Philip Moore, Julia Oxenbury, Margaret Palmer, C. A. Pearson, C. Pidgeon, M. Pujara, David Skipp, A. Smith, K. Tarrant, Chris Tibbott, Brett J. Whitby-Smith, Hamish Whitaker, Mary Anne Whitehead, P. R. Wilks, Sidney Worthington, and J. Young. University of Utrecht Network (the Netherlands): Atyvan Aarnhem, G. Ploosvan Amstel, D. B. van Baarda, Marja Baeten, P. J. van Beek, H. C. V. Berkum, R. Bohm, J. C. M. van Campen, J. W. Cirkel, H. J. R. Dorman, J. H. Duistermaat, H. van Es, N. Goudswaard, N. de Grunt, Ax. M. E. J. Hoeberichts, M. E. van der Hoek, J. M. P. M. Janssen, E. G. A. de Jong, L. Klaphake, A. W. K. Kramer, J. Kuiper, N. Kwakernaak, Hans Kootte, Jaap R. van der Laan, O. J. M. Lackamp, C. G. Lameris, Marjan Lamers, H. C. de Lathouder, P. J. Luyendijk, G. A. M. Maathuis, R. H. L. Morshuis, W. P. G. Mulder, P. L. W. Pijman, F. G. Pingen, Pricleer, Liesbeth Redeke, M. J. G. van Roosmalen, C. J. Rovers, S. H. A. Schmeets, J. F. Scholte, B. P. Schreuder, T. Steenkamer, Jette Timmer-Martijn, F. Trip, de Vries, Christine Weenink, H. C. P. M. van Weert, P. Willems, Boes Willemse, and P. van de Woestijne.