• 6499 Citations
  • 35 Scopus h-Index
20052020
If you made any changes in Pure, your changes will be visible here soon.

Research Output 2005 2020

1 Citation (Scopus)
Young Adult
Adenocarcinoma
Survival
Neoplasms
Age Groups
15 Citations (Scopus)

Yield of Repeat Endoscopy in Barrett’s Esophagus with No Dysplasia and Low-Grade Dysplasia: A Population-Based Study

Visrodia, K., Iyer, P. G., Schleck, C. D., Zinsmeister, A. R. & Katzka, D. A., May 9 2015, (Accepted/In press) In : Digestive Diseases and Sciences.

Research output: Contribution to journalArticle

Barrett Esophagus
Endoscopy
Adenocarcinoma
Population
Biopsy
2 Citations (Scopus)

Who Deserves Endoscopic Screening for Esophageal Neoplasia?

Blevins, C. H. & Iyer, P. G., 2017, (Accepted/In press) In : Gastrointestinal Endoscopy Clinics of North America.

Research output: Contribution to journalArticle

Barrett Esophagus
Neoplasms
Adenocarcinoma
Mortality
Incidence

What Constitutes Optimal Management of T1N0 Esophageal Adenocarcinoma?

Ramay, F. H., Vareedayah, A. A., Visrodia, K., Iyer, P. G., Wang, K. K. N., Eluri, S., Shaheen, N. J., Reddy, R., Martin, L. W., Greenwald, B. D. & Edwards, M. A., Jan 1 2019, (Accepted/In press) In : Annals of Surgical Oncology.

Research output: Contribution to journalArticle

Adenocarcinoma
Esophagectomy
Therapeutics
Barrett Esophagus
Survival
20 Citations (Scopus)

Variation in age at cancer diagnosis in familial versus nonfamilial Barrett's esophagus

Chak, A., Chen, Y., Vengoechea, J., Canto, M. I., Elston, R., Falk, G. W., Grady, W. M., Guda, K., Kinnard, M., Markowitz, S., Mittal, S., Iyer, P. G., Shaheen, N., Willis, J. E. & Barnholtz-Sloan, J. S., Feb 1 2012, In : Cancer Epidemiology Biomarkers and Prevention. 21, 2, p. 376-383 8 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Adenocarcinoma
Neoplasms
Tertiary Healthcare
Early Detection of Cancer
61 Citations (Scopus)

Utility of Biomarkers in Prediction of Response to Ablative Therapy in Barrett's Esophagus

Iyer, P. G., Wang, K. K. N., Halling, K. C., Buttar, N. S., Wongkeesong, L. M., Zinsmeister, A. R., Brankley, S. M., Fritcher, E. G. B., Westra, W. M., Krishnadath, K. K., Lutzke, L. S. & Borkenhagen, L. S., Aug 2008, In : Gastroenterology. 135, 2, p. 370-379 10 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Photochemotherapy
Biomarkers
Therapeutics
Odds Ratio
10 Citations (Scopus)
Adenocarcinoma
Survival
Neoplasms
Esophagectomy
Liver
20 Citations (Scopus)

Training in small-bowel capsule endoscopy: Assessing and defining competency

Rajan, E., Iyer, P. G., Oxentenko, A. S., Pardi, D. S., Alexander, J. A., Baron, T. H., Bruining, D. H., Hansel, S. L., Larson, M. V., Murray, J. A., Debritto, J., Dierkhising, R. A. & Gostout, C. J., Oct 2013, In : Gastrointestinal Endoscopy. 78, 4, p. 617-622 6 p.

Research output: Contribution to journalArticle

Capsule Endoscopy
Mental Competency
Capsules
Endoscopy
Gastroenterology
5 Citations (Scopus)

Timeline and location of recurrence following successful ablation in Barrett's oesophagus: An international multicentre study

Sami, S. S., Ravindran, A., Kahn, A., Snyder, D., Santiago, J., Ortiz-Fernandez-Sordo, J., Tan, W. K., Dierkhising, R. A., Crook, J., Heckman, M. G., Johnson, M. L., Lansing, R., Ragunath, K., Di Pietro, M., Wolfsen, H., Ramirez, F. C., Fleischer, D., Wang, K. K. N., Leggett, C., Katzka, D. A. & 1 others, Iyer, P. G., Jan 1 2018, (Accepted/In press) In : Gut.

Research output: Contribution to journalArticle

Barrett Esophagus
Multicenter Studies
Metaplasia
Recurrence
Esophagus
39 Citations (Scopus)

The Mayo Dysphagia Questionnaire-30: Documentation of reliability and validity of a tool for interventional trials in adults with esophageal disease

McElhiney, J., Lohse, M. R., Arora, A. S., Peloquin, J. M., Geno, D. M., Kuntz, M. M., Enders, F. T., Fredericksen, M., Abdalla, A. A., Khan, Y., Talley, N. J., Diehl, N. N., Beebe, T. J., Harris, A. M., Farrugia, G., Graner, D. E., Murray, J. A., Locke, G. R., Grothe, R. M., Crowell, M. D. & 10 others, Francis, D. L., Grudell, A. M. B., Dabade, T., Ramirez, A., Alkhatib, M., Alexander, J. A., Kimber, J., Iyer, P. G., Zinsmeister, A. R. & Romero, Y., Sep 2010, In : Dysphagia. 25, 3, p. 221-230 10 p.

Research output: Contribution to journalArticle

Esophageal Diseases
Deglutition Disorders
Reproducibility of Results
Documentation
Outpatients
5 Citations (Scopus)

The Esophageal Epithelial Barrier in Health and Disease

Blevins, C. H., Iyer, P. G., Vela, M. F. & Katzka, D. A., Jan 1 2017, (Accepted/In press) In : Clinical Gastroenterology and Hepatology.

Research output: Contribution to journalArticle

Health
Eosinophilic Esophagitis
Esophageal Diseases
Barrett Esophagus
Disease Management
22 Citations (Scopus)

The Effect of Endoscopic Surveillance in Patients With Barrett's Esophagus: A Systematic Review and Meta-analysis

Codipilly, D. C., Chandar, A. K., Singh, S., Wani, S., Shaheen, N. J., Inadomi, J. M., Chak, A. & Iyer, P. G., Jun 1 2018, In : Gastroenterology. 154, 8, p. 2068-2086.e5

Research output: Contribution to journalArticle

Barrett Esophagus
Meta-Analysis
Adenocarcinoma
Mortality
Survival
4 Citations (Scopus)

The African Esophageal cancer Consortium: A call to action

Van Loon, K., Mwachiro, M. M., Abnet, C. C., Akoko, L., Assefa, M., Burgert, S. L., Chasimpha, S., Dzamalala, C., Fleischer, D. E., Gopal, S., Iyer, P. G., Kaimila, B., Kayamba, V., Kelly, P., Leon, M. E., Mathew, C. G., Menya, D., Middleton, D., Mlombe, Y., Mmbaga, B. T. & 13 others, Mmbaga, E., Mulima, G., Murphy, G., Mushi, B., Mwanga, A., Mwasamwaja, A., Parker, M. I., Pritchett, N., Schüz, J., Topazian, M., White, R. E., McCormack, V. & Dawsey, S. M., Mar 1 2018, In : Journal of global oncology. 2018, 4

Research output: Contribution to journalArticle

Esophageal Neoplasms
Incidence
Capacity Building
Eastern Africa
Ethiopia

Targeting the COX1/2-Driven thromboxane A2 pathway suppresses Barrett's esophagus and esophageal adenocarcinoma development

Zhang, T., Wang, Q., Ma, W. Y., Wang, K., Chang, X., Johnson, M. L., Bai, R., Bode, A. M., Foster, N. R., Falk, G. W., Limburg, P. J., Iyer, P. G. & Dong, Z., Nov 2019, In : EBioMedicine. 49, p. 145-156 12 p.

Research output: Contribution to journalArticle

Open Access
Thromboxane A2
Barrett Esophagus
Biopsy
Aspirin
Adenocarcinoma
10 Citations (Scopus)

Systematic review with meta-analysis: prevalent vs. incident oesophageal adenocarcinoma and high-grade dysplasia in Barrett's oesophagus

Visrodia, K., Singh, S., Krishnamoorthi, R., Ahlquist, D. A., Wang, K. K. N., Iyer, P. G. & Katzka, D. A., Oct 1 2016, In : Alimentary Pharmacology and Therapeutics. 44, 8, p. 775-784 10 p.

Research output: Contribution to journalReview article

Barrett Esophagus
Meta-Analysis
Adenocarcinoma
Confidence Intervals
MEDLINE
1 Citation (Scopus)

Systematic review and meta-analysis of prevalence and risk factors for Barrett's esophagus

Qumseya, B. J., Bukannan, A., Gendy, S., Ahemd, Y., Sultan, S., Bain, P., Gross, S. A., Iyer, P. G. & Wani, S., Jan 1 2019, (Accepted/In press) In : Gastrointestinal endoscopy.

Research output: Contribution to journalReview article

Barrett Esophagus
Meta-Analysis
Confidence Intervals
Gastroesophageal Reflux
Population
101 Citations (Scopus)
Hydroxymethylglutaryl-CoA Reductase Inhibitors
Barrett Esophagus
Esophageal Neoplasms
Meta-Analysis
Odds Ratio
18 Citations (Scopus)

Spontaneous perforation in the ringed esophagus

Iyer, P. G. & Arora, A. S., Dec 1 2005, In : Diseases of the Esophagus. 18, 6, p. 406-409 4 p.

Research output: Contribution to journalArticle

Esophagus
Eosinophilic Esophagitis
Deglutition Disorders
Gastroesophageal Reflux
Tears
64 Citations (Scopus)

Significance of neoplastic involvement of margins obtained by endoscopic mucosal resection in Barrett's esophagus

Iyer, P. G., Buttar, N. S., Wongkeesong, L. M., Lewis, J. T., Sanderson, S. O., Lutzke, L. S., Borkenhagen, L. S. & Wang, K. K. N., Nov 2007, In : American Journal of Gastroenterology. 102, 11, p. 2380-2386 7 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Esophagectomy
Carcinoma
Surgical Pathology
Neoplasm Staging
13 Citations (Scopus)

Screening for esophageal squamous cell carcinoma: recent advances

Codipilly, D. C., Qin, Y., Dawsey, S. M., Kisiel, J. B., Topazian, M., Ahlquist, D. & Iyer, P. G., Jan 1 2018, (Accepted/In press) In : Gastrointestinal Endoscopy.

Research output: Contribution to journalArticle

Esophageal Squamous Cell Carcinoma
18 Citations (Scopus)

Screening for barrett's esophagus and esophageal adenocarcinoma: Rationale, recent progress, challenges, and future directions

Sami, S. S., Ragunath, K. & Iyer, P. G., Apr 1 2015, In : Clinical Gastroenterology and Hepatology. 13, 4, p. 623-634 12 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Adenocarcinoma
Biomarkers
Mortality
Direction compound
2 Citations (Scopus)

Screening for Barrett's Esophagus

Gupta, M. & Iyer, P. G., Jun 1 2015, In : Gastroenterology Clinics of North America. 44, 2, p. 265-283 19 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Health Services Needs and Demand
Adenocarcinoma
9 Citations (Scopus)

Screening for Barrett's esophagus: Results from a population-based survey

Gupta, M., Beebe, T. J., Dunagan, K. T., Schleck, C. D., Zinsmeister, A. R., Talley, N. J., Locke, G. R. & Iyer, P. G., 2014, In : Digestive Diseases and Sciences. 59, 8, p. 1831-1850 20 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Population
Endoscopy
Adenocarcinoma
Capsule Endoscopy
49 Citations (Scopus)

Safety of Prior Endoscopic Mucosal Resection in Patients Receiving Radiofrequency Ablation of Barrett's Esophagus

Okoro, N. I., Tomizawa, Y., Dunagan, K. T., Lutzke, L. S., Wang, K. K. N. & Iyer, P. G., Feb 2012, In : Clinical Gastroenterology and Hepatology. 10, 2, p. 150-154 5 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Safety
Pathologic Constriction
Metaplasia
Odds Ratio
40 Citations (Scopus)

Safety of endoscopic mucosal resection for Barrett's esophagus

Tomizawa, Y., Iyer, P. G., Wong Kee Song, L. M., Buttar, N. S., Lutzke, L. S. & Wang, K. K. N., Sep 2013, In : American Journal of Gastroenterology. 108, 9, p. 1440-1447 8 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Safety
Pathologic Constriction
Endoscopic Mucosal Resection
Hemorrhage
3 Citations (Scopus)

Safety, Diagnostic Accuracy, and Effects of Endoscopic Ultrasound Fine-Needle Aspiration on Detection of Extravascular Migratory Metastases

Rustagi, T., Gleeson, F. C., Chari, S. T., Lehrke, H. D., Takahashi, N., Malikowski, T. M., Abu Dayyeh, B. K., Chandrasekhara, V., Iyer, P. G., Kendrick, M. L., Pearson, R. K., Petersen, B. T., Rajan, E., Smoot, R. L., Storm, A. C., Topazian, M. D., Truty, M. J., Vege, S. S., Wang, K. K. & Levy, M. J., Nov 2019, In : Clinical Gastroenterology and Hepatology. 17, 12, p. 2533-2540.e1

Research output: Contribution to journalArticle

Fine Needle Biopsy
Neoplasm Metastasis
Safety
Tomography
Magnetic Resonance Imaging
11 Citations (Scopus)

Role of Obesity in the Pathogenesis and Progression of Barrett's Esophagus

Chandar, A. K. & Iyer, P. G., Jun 1 2015, In : Gastroenterology Clinics of North America. 44, 2, p. 249-264 16 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Abdominal Obesity
Obesity
Inflammation
Insulin Resistance
3 Citations (Scopus)

Rodent endosonography to monitor esophageal cancer

Buttar, N. S., Wiersema, M. J., Wang, K. K. N., DeMars, C. J., Iyer, P. G. & Lutzke, L. S., Jun 2006, In : International Journal of Gastrointestinal Cancer. 37, 2-3, p. 84-90 7 p.

Research output: Contribution to journalArticle

Endosonography
Esophageal Neoplasms
Rodentia
Ultrasonography
Neoplasms
12 Citations (Scopus)

RNA sequencing identifies transcriptionally viable gene fusions in esophageal adenocarcinomas

Blum, A. E., Venkitachalam, S., Guo, Y., Kieber-Emmons, A. M., Ravi, L., Chandar, A. K., Iyer, P. G., Canto, M. I., Wang, J. S., Shaheen, N. J., Barnholtz-Sloan, J. S., Markowitz, S. D., Willis, J. E., Shyr, Y., Chak, A., Varadan, V. & Guda, K., Oct 1 2016, In : Cancer Research. 76, 19, p. 5628-5633 6 p.

Research output: Contribution to journalArticle

RNA Sequence Analysis
Gene Fusion
Adenocarcinoma
Autophagy
Barrett Esophagus
35 Citations (Scopus)

Risk of recurrence of Barrett's esophagus after successful endoscopic therapy

Krishnamoorthi, R., Singh, S., Ragunathan, K., Katzka, D. A., Wang, K. K. N. & Iyer, P. G., Jun 1 2016, In : Gastrointestinal Endoscopy. 83, 6, p. 1090-1106 17 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Metaplasia
Recurrence
Adenocarcinoma
Therapeutics
1 Citation (Scopus)

Risk of progression in Barrett's esophagus indefinite for dysplasia: a systematic review and meta-analysis

Krishnamoorthi, R., Mohan, B. P., Jayaraj, M., Wang, K. K. N., Katzka, D. A., Ross, A., Adler, D. G. & Iyer, P. G., Jan 1 2019, (Accepted/In press) In : Gastrointestinal endoscopy.

Research output: Contribution to journalReview article

Barrett Esophagus
Meta-Analysis
Adenocarcinoma
Incidence
Cohort Studies

Response to Syed et al.

Sami, S. S., Ragunath, K. & Iyer, P. G., Jun 10 2015, In : American Journal of Gastroenterology. 110, 6, p. 937-938 2 p.

Research output: Contribution to journalArticle

Digestive System Endoscopy
Mass Screening
Barrett Esophagus

Response to Kosmidou et al.

Iyer, P. G. & Ahlquist, D. A., Jan 1 2018, (Accepted/In press) In : American Journal of Gastroenterology.

Research output: Contribution to journalArticle

Response:

Codipilly, D. C., Qin, Y., Dawsey, S. M., Kisiel, J. B., Topazian, M., Ahlquist, D. & Iyer, P. G., Feb 1 2019, In : Gastrointestinal Endoscopy. 89, 2, 1 p.

Research output: Contribution to journalLetter

Response

Krishnamoorthi, R., Borah, B. J., Heien, H., Das, A., Chak, A. & Iyer, P. G., Feb 1 2017, In : Gastrointestinal Endoscopy. 85, 2, p. 463-464 2 p.

Research output: Contribution to journalLetter

Response

Singh, S., Manickam, P., Iyer, P. G. & Desai, T. K., Feb 1 2015, In : Gastrointestinal Endoscopy. 81, 2, p. 484-485 2 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Esophageal Neoplasms
Adenocarcinoma

Reply

Iyer, P. G., Mar 1 2011, In : Clinical Gastroenterology and Hepatology. 9, 3, p. 277-278 2 p.

Research output: Contribution to journalLetter

Reply

Leggett, C. & Iyer, P. G., 2014, In : Clinical Gastroenterology and Hepatology. 12, 6, p. 1056 1 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Obstructive Sleep Apnea
12 Citations (Scopus)

Remote malignant intravascular thrombi: EUS-guided FNA diagnosis and impact on cancer staging

Rustagi, T., Gleeson, F. C., Chari, S. T., Abu Dayyeh, B. K., Farnell, M. B., Iyer, P. G., Kendrick, M. L., Pearson, R. K., Petersen, B. T., Rajan, E., Topazian, M., Truty, M., Vege, S. S., Wang, K. K. N. & Levy, M. J., Aug 16 2016, (Accepted/In press) In : Gastrointestinal Endoscopy.

Research output: Contribution to journalArticle

Endoscopic Ultrasound-Guided Fine Needle Aspiration
Neoplasm Staging
Thrombosis
Cell Biology
Magnetic Resonance Imaging
158 Citations (Scopus)

Recurrence of esophageal intestinal metaplasia after endoscopic mucosal resection and radiofrequency ablation of Barrett's esophagus: Results from a us multicenter consortium

Gupta, M., Iyer, P. G., Lutzke, L., Gorospe, E. C., Abrams, J. A., Falk, G. W., Ginsberg, G. G., Rustgi, A. K., Lightdale, C. J., Wang, T. C., Fudman, D. I., Poneros, J. M. & Wang, K. K. N., Jul 2013, In : Gastroenterology. 145, 1

Research output: Contribution to journalArticle

Barrett Esophagus
Metaplasia
Recurrence
Endoscopic Mucosal Resection
Biopsy
3 Citations (Scopus)

Recent developments in pathogenesis, diagnosis and therapy of Barrett's esophagus

Halland, M., Katzka, D. A. & Iyer, P. G., Jun 7 2015, In : World Journal of Gastroenterology. 21, 21, p. 6479-6490 12 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Western World
Cost of Illness
Adenocarcinoma
Therapeutics
23 Citations (Scopus)

Rates and predictors of progression to esophageal carcinoma in a large population-based Barrett's esophagus cohort

Krishnamoorthi, R., Borah, B. J., Heien, H., Das, A., Chak, A. & Iyer, P. G., Aug 30 2015, (Accepted/In press) In : Gastrointestinal Endoscopy.

Research output: Contribution to journalArticle

Barrett Esophagus
Esophageal Neoplasms
Carcinoma
Population
Hydroxymethylglutaryl-CoA Reductase Inhibitors
35 Citations (Scopus)

Radiofrequency Ablation Is Associated with Decreased Neoplastic Progression in Patients with Barrett's Esophagus and Confirmed Low-Grade Dysplasia

Small, A. J., Araujo, J. L., Leggett, C., Mendelson, A. H., Agarwalla, A., Abrams, J. A., Lightdale, C. J., Wang, T. C., Iyer, P. G., Wang, K. K. N., Rustgi, A. K., Ginsberg, G. G., Forde, K. A., Gimotty, P. A., Lewis, J. D., Falk, G. W. & Bewtra, M., Sep 1 2015, In : Gastroenterology. 149, 3, p. 567e3-576e3

Research output: Contribution to journalArticle

Barrett Esophagus
Adenocarcinoma
Endoscopy
Selection Bias
Retrospective Studies
6 Citations (Scopus)

Putting it Through the Nose: The Ins and Outs of Transnasal Endoscopy

Blevins, C. H. & Iyer, P. G., Aug 16 2016, (Accepted/In press) In : American Journal of Gastroenterology.

Research output: Contribution to journalArticle

8 Citations (Scopus)

Prospective evaluation of adverse events following lower gastrointestinal tract EUS FNA

Levy, M. J., Abu Dayyeh, B. K., Fujii, L. L., Boardman, L. A., Clain, J. E., Iyer, P. G., Rajan, E., Topazian, M., Wang, K. K. N., Wiersema, M. J. & Gleeson, F. C., 2014, In : American Journal of Gastroenterology. 109, 5, p. 676-685 10 p.

Research output: Contribution to journalArticle

Lower Gastrointestinal Tract
Fine Needle Biopsy
Odds Ratio
Confidence Intervals
Pain
15 Citations (Scopus)

Prevalence of esophageal eosinophils in patients with barrett's esophagus

Ravi, K., Katzka, D. A., Smyrk, T. C., Iyer, P. G., Romero, Y., Francis, D. L., Lutzke, L., Tian, J. & Wang, K. K. N., May 2011, In : American Journal of Gastroenterology. 106, 5, p. 851-857 7 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Eosinophils
Eosinophilia
Eosinophilic Esophagitis
Gastroesophageal Reflux
44 Citations (Scopus)

Prevalence and predictors of recurrent neoplasia after ablation of Barrett's esophagus

Badreddine, R. J., Iyer, P. G., Wang, K. K. N., Wong Kee Song, L. M., Buttar, N. S., Dunagan, K. T., Lutzke, L. S. & Borkenhagen, L. S., Apr 2010, In : Gastrointestinal Endoscopy. 71, 4, p. 697-703 7 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Recurrence
Neoplasms
Photochemotherapy
Smoking
7 Citations (Scopus)

Prevalence and Predictors of Gastroesophageal Reflux Complications in Community Subjects

Crews, N. R., Johnson, M. L., Schleck, C. D., Enders, F. T., Wongkeesong, L. M., Wang, K. K. N., Katzka, D. A. & Iyer, P. G., Aug 10 2016, (Accepted/In press) In : Digestive Diseases and Sciences. p. 1-8 8 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Gastroesophageal Reflux
Esophagitis
Abdominal Obesity
Tobacco Use
215 Citations (Scopus)

Prevalence and predictive factors of eosinophilic esophagitis in patients presenting with dysphagia: A prospective study

Iyer, P. G., Talley, N. J., Romero, Y., Arora, A. S., Kryzer, L. A., Smyrk, T. C. & Alexander, J. A., Dec 2007, In : American Journal of Gastroenterology. 102, 12, p. 2627-2632 6 p.

Research output: Contribution to journalArticle

Eosinophilic Esophagitis
Deglutition Disorders
Prospective Studies
Biopsy
Endoscopy
71 Citations (Scopus)

Predictors of stricture formation after photodynamic therapy for high-grade dysplasia in Barrett's esophagus{A figure is presented}

Iyer, P. G., Wang, K. K. N., Buttar, N. S., Wongkeesong, L. M., Lutzke, L. S. & Borkenhagen, L. S., Jan 2007, In : Gastrointestinal Endoscopy. 65, 1, p. 60-66 7 p.

Research output: Contribution to journalArticle

Barrett Esophagus
Photochemotherapy
Pathologic Constriction
Esophageal Stenosis
Odds Ratio