Data analysis 3

Readings

Comprehensive and easy to understand references on this area are difficult to find, hence the large list of recommended reading below.

Linear regression

• Shott, S (1991) Statistics simplified - regression. Journal of the American Veterinary Medical Association 198: 798 - 801.
• Dohoo I, Martin S, Stryhn H (2003) Veterinary Epidemiologic Research. AVC Inc, Charlottetown, Prince Edward Island, Canada. pp 273 - 313.

Logistic regression

• Shott S (1990) Statistics simplified - logistic regression and discriminant analysis. Journal of the American Veterinary Medical Association, 198: 1902 - 1905.
• Bennett, D (2001) Logistic regression analysis: an epidemiological perspective. Australasian Epidemiologist 8: 38 - 44.
• Dohoo I, Martin S, Stryhn H (2003) Veterinary Epidemiologic Research. AVC Inc, Charlottetown, Prince Edward Island, Canada. pp 335 - 370.

Survival analysis

• Shott S (1990) Statistics simplified - survival analysis. Journal of the American Veterinary Medical Association, 198: 1513 - 1515.
• Dohoo I, Martin S, Stryhn H (2003) Veterinary Epidemiologic Research. AVC Inc, Charlottetown, Prince Edward Island, Canada. pp 409 - 424.
• Stevenson M (2007) An Introduction to Survival Analysis: 195.721 Study Guide. Massey University, Palmerston North, New Zealand. pp 1 - 31.

Meta analysis

• Egger M, Davey Smith G (1997) Meta-analysis: Potentials and promise. British Medical Journal 315: 1371 - 1374.
• Thrusfield M (2005) Veterinary Epidemiology. Blackwell Science, London. pp 300 - 304.
• Dohoo I, Martin S, Stryhn H (2003) Veterinary Epidemiologic Research. AVC Inc, Charlottetown, Prince Edward Island, Canada. pp 543 - 558.
• Cochrane Collaboration Open Learning Material for Reviewers. Chapter 3.

Presentations

Choose one of the statistical techniques listed above (linear regression, logistic regression, survival analysis, meta-analysis). Imagine you are to give a 20 minute presentation about this technique to a group of colleagues who know very little about epidemiology (or statistics). Your talk should include:

• A description of what the technique is used for.
• A [brief] description of the principles and assumptions that underpin the technique.
• Examples of where the technique has been used to provide insight into an animal health problem.
• What to look out for when evaluating studies that have used the technique.

Exercises

Critically appraise three or more of the following four studies, describe the following:

1. Objectives of the analysis;
2. The unit(s) of analysis;
3. Types of data (outcome and exposure variables); and
4. The type of analysis used (linear regression, logistic regression, survival analysis, meta-analysis) and why that approach was appropriate;

• Arunvipas P, Dohoo I, VanLeeuwen J, Keefe G (2003) The effect of non-nutritional factors on milk urea nitrogen levels in dairy cows in Prince Edward Island, Canada. Preventive Veterinary Medicine 59, 83 - 93.
• Borges V, Bernardi M, Bortolozzo F, Wentz I (2005) Risk factors for stillbirth and foetal mummification in four Brazilian swine herds. Preventive Veterinary Medicine 70, 165 - 176 [logistic regression].
• Matsuda R, Morizane T, (2005) Helicobacter pylori infection in dental professionals:A 6-year prospective study. Helicobacter 10, 307 - 311 [logistic regression].
• Proudman C, Smith J, Edwards G, French N (2002) Long-term survival of equine surgical colic cases. Part 1: Patterns of mortality and morbidity. Equine Veterinary Journal 34, 432 - 437 [survival analysis].
• Rabiee AR, Lean IJ, Stevenson MA (2004) A Bayesian meta-analysis of the effects of administering an intra-vaginal (CIDR) device in combination with other hormones on the reproductive performance of cycling, anoestrous and inseminated cows. New Zealand Veterinary Journal 52 (6): 384 - 393.
• Wilesmith JW, Ryan J BM, Stevenson MA, Morris RS, Pfeiffer DU, Lin D, Jackson R, Sanson RL (2000) Temporal aspects of the epidemic of bovine spongiform encephalopathy in Great Britain: holding-associated risk factors for the disease. Veterinary Record 147 (12): 319 - 325.
• Singer ER, Saxby F, French NP (2003) A retrospective case-control study of horse falls in the sport of horse trials and three-day eventing. Equine Veterinary Journal 35 (2): 139 - 145.
• Charlier J, Claerebout E, Muelenaere E. de, Vercruysse J (2005) Associations between dairy herd management factors and bulk tank milk antibody levels against Ostertagia ostertagi. Veterinary Parasitology 133 (1): 91 - 100.
• Sanchez J, Dohoo I, Carrier J, DesCoteaux L (2004) A meta-analysis of the milk-production response after anthelmintic treatment in naturally infected adult dairy cows. Preventive Veterinary Medicine 63, 237 - 256 [meta-analysis].

Example examination questions

1. Describe the application, advantages and limitations of linear regression in veterinary epidemiology.
2. Describe the application, advantages and limitations of logistic regression in veterinary epidemiology.
3. Briefly describe the essential features and application of survival analysis (2003 written).
4. Describe the application, advantages and limitations of meta-analysis (2005 oral).

Additional reading

• Noordhuizen J, Frankena K, van der Hoofd C, Graat E (1997) Application of Quantitative Methods in Veterinary Epidemiology. Wageningen Pers, Wageningen pp 135 - 178 [logistic regression].
• Ottenbacher K, Ottenbacher H, Tooth L, Ostir G (2004) A review of two journals found that articles using multivariable logistic regression frequently did not report commonly recommended assumptions. Journal of Clinical Epidemiology 57, 1147 - 1152 [logistic regression].
• Noordhuizen J, Frankena K, van der Hoofd C, Graat E (1997), Application of Quantitative Methods in Veterinary Epidemiology. Wageningen Pers, Wageningen pp 179 - 214 [survival analysis].