UQUMRC KAMC Biostatistics for your Research Proposal 2012

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A brief presentation on important statistics concepts for research proposals. Given for the UQU Medical Research Club "Your Journey Towards Research" held at King Abdullah Medical City, Makkah. May 17, 2012

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UQUMRC KAMC Biostatistics for your Research Proposal 2012

  1. 1. Statistics for Your Research Proposal SohailBajammal, MBChB, MSc, FRCS(C), PhD(c) Assistant Professor of Orthopaedics, Umm Al-Qura UniversityDirector of CME & Research Administration, King Abdullah Medical City Makkah bajammal
  2. 2. What Statistics do you need to know for your proposal?• Types of Variables• Types of Statistics• How to Choose a Statistical Test?• Hypothesis Testing & Sample Size
  3. 3. Patho Physiology of Research Research Study Plan Actual Study Question Design Implement Target Intended Actual subjects Population Sample Errors Errors Actual Phenomena Intended measurements of interest variablesTruth in the Truth in the Findings in Universe Infer Study Infer the Study External Validity Internal Validity From Hulley et al. Designing Clinical Research. LWW
  4. 4. Variables
  5. 5. Variables• Anything whose value can vary• Dependent (response) variable: outcome• Independent (explanatory) variables: predictors• Confounding variable: associated with the independent variable and a cause of the dependent variable – coffee drinking (independent), MI (dependent) – cigarette smoking (confounder),
  6. 6. Types of Variables Categorical Quantitative (Continuous or “Qualitative” Discrete)Nominal Ordinal Interval RatioNationality Stage I, II, III Temperature Pulse Gender & IV cancer (0 is not zero) (0 is dead)
  7. 7. Types of Variables Categorical Quantitative (Continuous or “Qualitative” Discrete)Nominal Ordinal Interval RatioNationality Stage I, II, III Temperature Pulse Gender & IV cancer (0 is not zero) (0 is dead)
  8. 8. Types of Variables Categorical Quantitative (Continuous or “Qualitative” Discrete)Nominal Ordinal Interval RatioNationality Stage I, II, III Temperature Pulse Gender & IV cancer (0 is not zero) (0 is dead)
  9. 9. Types of Variables Categorical Quantitative (Continuous or “Qualitative” Discrete)Nominal Ordinal Interval RatioNationality Stage I, II, III Temperature Pulse Gender & IV cancer (0 is not zero) (0 is dead)
  10. 10. Implications of Types of Variable• Details of data collection forms – Age: • ……. Years Ratio • <20yr, 21-30yr, 31-40yr, >40 Ordinal• Choice of statistical analysis test• Coding in the statistical software: 1,2 for nominal – Does not make sense to have a mean for nominal• BIAS if you didn’t consider confounders
  11. 11. When deciding on your variables• Think of patient-oriented outcomes, instead of disease-oriented outcomes• Studying the effect of new drugs on arrhythmia, which is better as outcome? – Number of arrhythmia – Frequency of palpitation/Quality of Life
  12. 12. Statistics
  13. 13. Statistics deals with• Collection• Organization• Analysis Data• Interpretation
  14. 14. Types of Statistics Statistics Descriptive Inferential Statistics Statistics Measures Measures What Confidence of Central Interval of Spread test? Tendency Inter- StandardMean Median Mode quartile Deviation Range
  15. 15. Types of Statistics Statistics Descriptive Inferential Statistics Statistics Measures Measures What Confidence of Central Interval of Spread test? Tendency Inter- StandardMean Median Mode quartile Deviation Range
  16. 16. Types of Statistics Statistics Descriptive Inferential Statistics Statistics Measures Measures What Confidence of Central Interval of Spread test? Tendency Inter- StandardMean Median Mode quartile Deviation Range
  17. 17. Descriptive Statistics• Numerical• Tabulated• Graphs
  18. 18. Measures of Central Tendency• Mean: average• Mode: most frequent count• Median: the value separating the top and bottom of data (organized highest to lowest)
  19. 19. Measures of Central Tendency Best measure ofType of Variable central tendency Nominal Mode Ordinal Median Interval/ratio Mean (not skewed) Interval/ratio Median (skewed)
  20. 20. Difficult Exam Scores!!Laerd.com
  21. 21. Measures of Spread (Variability)• Standard Deviation• Percentile• Range &Interquartile Range
  22. 22. Standard Deviation Variability of values around the mean Variance Standard Deviation Courtesy of Prof. Hassan Baaqeel
  23. 23. Differences in Standard Deviation Bell-shaped curve 0.08 0.07 Mean = 70 SD = 5 0.06 0.05Density 0.04 Mean = 70 SD = 10 0.03 0.02 0.01 0.00 40 50 60 70 80 90 100 Grades
  24. 24. Normal Distribution MEAN 68 % of observations 1 SD 2 SD 95 % of observations 99.7 % of observations 3D-3 -2 -1 0 1 2 3 STANDARD DEVIATIONS Courtesy of Prof. Hassan Baaqeel
  25. 25. Types of Statistics Statistics Descriptive Inferential Statistics Statistics Measures Measures What Confidence of Central Interval of Spread test? Tendency Inter- StandardMean Median Mode quartile Deviation Range
  26. 26. Inferential Statistics• Allow for making predictions, estimations or inferences about what has not been observed (the whole population) based on what has (the sample)• Every time we use inferential statistics we risk being wrong by chance – We need a range of values to be confident (Confidence Interval)
  27. 27. Patho Physiology of Research Research Study Plan Actual Study Question Design Implement Target Intended Actual subjects Population Sample Errors Errors Actual Phenomena Intended measurements of interest variablesTruth in the Truth in the Findings in Universe Infer Study Infer the Study External Validity Internal Validity From Hulley et al. Designing Clinical Research. LWW
  28. 28. Hypothesis Testing• When we compare two groups, we are testing a hypothesis• Null Hypothesis (HO): – there is no difference between the groups – (e.g., no difference in mortality)• Alternate Hypothesis (HA): – there is a difference• We choose a statistical test to do the hypothesis testing
  29. 29. Chi-squareMann-Whitney Statistical Tests t-test Kruskal-Wallis ANOVA
  30. 30. How to Choose a Statistical Test?• Your Question: – Difference between groups or correlation/prediction• Variables: – Types: nominal, ordinal, interval or ratio – Distribution: normal or skewed• Groups: – Number: two or more – Relationship: related or un-related
  31. 31. Brookes University
  32. 32. Bates College
  33. 33. Probably the simplest/coolest City College Coventry
  34. 34. Choice of Statistical Tests Parametric Non-Parametric Tests Tests Interval/Ratio 1. Ordinal Goal (normal 2. Interval/Ratio Nominal distribution) (skewed)Comparison of 2 Unpairedt-test Mann-Whitney Uunrelated groups Chi-square TestComparison of >2 ANOVA Kruskal-Wallis HunrelatedComparison of 2 Paired t-test Wilcoxonrelated groups Binomial Sign TestComparison of >2 Repeated measures Friedmanrelated groups ANOVACorrelation Pearson’s Spearman’s rho Chi-square Test
  35. 35. All the inferential tests are “estimation”• We need a CONFIDENCE INTERVAL• It is a range of values that if the estimate occurs in this range, we will be confident that it is not due to chance• How much error are we willing to accept ? – α< 0.05
  36. 36. Paul Mathews, Design of Experiments with MINITAB, 2005, ASQ Press
  37. 37. Hypothesis Testing (α&β errors)Null Hypothesis: No association between predictor & outcome Truth in the Population Results in the Study Sample Association Between No Association Between Predictor & Outcome Predictor & Outcome Reject null Correct Type I error (α) hypothesis Fail to reject null Type II error (β) Correct hypothesis
  38. 38. Type I & II Errors• Type I (α) Error: usually 1-5% – Rejecting the null hypothesis when it is actually true – Stating that there is a difference, while in truth there is no difference• Type II (β) Error: usually 10-20% – Failing to reject null hypothesis when it is actually false – Stating that there is no difference, while in truth there is a difference – Statistical Power of the Study = 1-β
  39. 39. Zazzle.com
  40. 40. Resources
  41. 41. What do you need to know in statistics for your proposal?• Types of Variables• Types of Statistics• How to Choose a Statistical Test?• Sample Size bajammal

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