1、Biostatistics in ObstetricsMitra Ahmad Soltani2008,In the Name of God,Med-ed-online.org,References:,Ahmad Soltani M. Regression Analysis of Labor Duration. The Internet Journal of Gynecology and Obstetrics. Texas: Vol 5, No 2. 2006 Clements JM. Synergy Medical Education Alliance Research Design Core
2、 Curriculum. Module2 2005,Birth rate,number of births 1000 populationIt includes men in the population.,Fertility Rate,number of live births1000 women aged 15-44 years While a woman with 2 second-trimester miscarriages would be considered fertile, her deliveries would not be included in the fertilit
3、y rate.,Reproductive Mortality rate,contraceptive use plus direct maternal deaths100000 women This is perhaps the most sensitive measure of a populations ability to provide safety for women.,Maternal Mortality Rate,number of direct or indirect maternal deaths 100,000 live births A condition in which
4、 both mother and fetus are lost would both increase the numerator (maternal death) and decrease the denominator (live birth).,Infant Mortality Rate,infants who die prior to their first birthday1000 live BirthsIMR is often one of the sentinel indicators used to evaluate a populations overall health a
5、nd access to health care.,Neonatal Mortality Rate,losses between 0-28 d of life (inclusive) 1000 live births This rate is often divided into early (first 7 d) and late (8-28 d) rates, as etiologies within these 2 categories vary somewhat.,Fetal Death rate (stillbirth rate),number of stillbirths 1000
6、 infants (total Births)Infants means “live and still” born.,Perinatal Mortality Rate,Fetal deaths+neonatal deaths 1000 total Births,Still birth,Delivery after 20 weeks EGA (and more than 500 g birthweight) in which the infant displays no sign of life (gasping, muscular activity, cardiac activity) is
7、 considered a stillbirth.,Live Birth,Delivery after 20 weeks EGA in which any activity is noted is classified as a live birth. This is a difficult definition, as the lower limit of reasonable viability currently remains around 23 weeks EGA. Thus, a spontaneous delivery at 21 weeks EGA with reflex mo
8、tion but no ability to survive with or without intervention would nonetheless be considered a live birth.,Abortion,The most common definition of an abortion is any loss of a fetus that is less than 20 weeks completed gestational age (since last menstrual period) or that weighs less than 500 grams.,P
9、reterm Infants,Preterm infant is another arbitrary definition because a subtle gradient of maturity exists. Most states define premature as a delivery before 37 completed weeks gestational age, although the vast majority of babies born after 35 weeks GA have uncomplicated perinatal courses.,Postterm
10、 Infants,The generally accepted definition of a postterm pregnancy is one that progresses beyond 42 weeks completed gestational age based on last menstrual period (LMP). In practice, many clinicians use a lower cutoff such as 41 weeks GA when LMP is certain.,Testing for statistical significance of t
11、he difference for nominal data,Small unmatched sample: Fishers exact test Small matched sample: Sign test Large unmatched sample: Chi-square, with Yates correction Large matched sample:McNemars test,Testing for statistical significance of the difference for ordinal data,One comparison(2 groups),unma
12、tched sample: Mann-Whitney U One comparison(2 groups)Matched sample:Wilcoxon matched pairs More than 2 groups unmatched sample: Kruskal Wallis one-way ANOVA More than 2 groups matched sample: Friedman 2-way ANOVA,Testing for statistical significance of the difference for continuous data,One comparis
13、on(2 groups)unmatched sample: t-test One comparison(2 groups)matched sample: matched t-test More than two groups unmatched sample:F test for analysis of variance followed by pairwise comparisons More than two groups matched sample: F test for analysis with blocking or analysis of covariance,Measure
14、the size of difference,Nominal/ordinal data: differences in proportions or percentages in each category Continuous data: Differences in mean values between the groups+ SD for each group,Tests to Determine Association Between Groups Measure the degree of Association,Nominal data: odds Ratio/Relative
15、Risk Ordinal Data(nonlinear):Spearmans rho/Kendalls tau Continuous Data: Pearsons Correlation Coefficient ( r ),Tests to Determine Association Between Groups testing for statistical significance of association,Nominal Data: Statistical Significance of odds Ratio Ordinal data(nonlinear): Statistical
16、Significance of rho or tau Continuous Data(linear):Statistical significance of Pearsons r,Tests to Determine Association Between Groups- Extent Association Explains Variation Between Groups,Nominal data: Attributable Risk Ordinal data(nonlinear):Spearmans rho or Kendalls tau Continuous data(linear):
17、Pearsons coefficient of determination,For describing one group,Mean, SD for measurement of Parametric Distributions Median, interquartile range for rank,score or measurement of non-parametric distributions Proportion for Binominal (2 possible outcomes),Compare one group to a hypothetical value,One s
18、ample t-test for measurement of Parametric Distributions Wilcoxon test for rank,score or measurement of non-parametric distributions Chi-square for Binominal (2 possible outcomes),Compare two unpaired groups,Unpaired t-test for measurement of Parametric Distributions Mann-Whitney test for rank, scor
19、e or measurement of non-parametric distributions Fischer test(or chi-square for large samples) for Binominal (2 possible outcomes),Compare two paired groups,Paired t-test for measurement of Parametric Distributions Wilcoxon test for rank, score or measurement of non-parametric distributions McNemars
20、 test for Binominal (2 possible outcomes),Compare three or more unmatched groups,One-way ANOVA for measurement of Parametric Distributions Kruskal Wallis test for rank, score or measurement of non-parametric distributions Chi-square for Binominal (2 possible outcomes),Compare three or more matched g
21、roups,Repeated measures ANOVA for measurement of Parametric Distributions Friedman test for rank, score or measurement of non-parametric distributions Cochrane Q for Binominal (2 possible outcomes),Quantify association between two variables,Pearson Correlation for measurement of Parametric Distribut
22、ions Spearman Correlation for rank, score or measurement of non-parametric distributions Contingency coefficients for Binominal (2 possible outcomes),Predict value from another measured variable,Simple linear regression or non-linear regression for measurement of Parametric Distributions Non-paramet
23、ric regression for rank, score or measurement of non-parametric distributions Simple logistic regression for Binominal (2 possible outcomes),Predict value from several measured or binominal variables,Multiple linear or nonlinear regression for measurement of Parametric Distributions Multiple logisti
24、c regression for Binominal (2 possible outcomes),summary,P=parametric/N=nonparametric/B=binominal M=matched/ U=unmatched/G=group/=versus/ H=Hypothetical value,Statistics Related to Diagnostic Tests,Sensitivity = True Positives/(True Positives + False Negatives)Specificity = True Negatives/(False Pos
25、itives + True Negatives)Positive Predictive Value = True Positive/(True Positive + False Positive)Negative Predictive Value = True Negative/(True Negative+False Negative),Likelihood Ratio = compares the likelihood of a result in a patients with the disease to the likelihood of a result in patients w
26、ithout disease.Positive LR = (a/a+c)/(b/b+d)Negative LR = (c/a+c)/(d/b+d),How much do LRs change disease likelihood?, LRs10 or 0.1 cause large changes in likelihood LRs 5-10 or 0.1-0.2 cause moderate changes LRs 2-5 or 0.2-0.5 cause small changes LRs between 2 and 0.5 cause little or no changes,Stat
27、istics to Interpret Importance &Precision of Therapeutic Results,Control Event Rate (CER) = c/(c+d)Experimental Event Rate (EER) = a/(a+b)Relative Risk (RR) = EER/CER = (a/a+b)/(c/c+d)Relative Risk Reduction (RRR) = CER-EER/CERAbsolute Risk Reduction (ARR) = CER-EERNumber Needed to Treat (NNT) = 1/A
28、RR,Relative Risk and Odds ration,There is strong association of RR or OR1 There is strong association if RR3 or OR4,Sample size,If dependent variable is nominal or ordinal: n= p (1-p) /d If dependent variable is continuous: n=s/d,Regression analysis of labor duration (A sample research),Introduction
29、 Determining labor duration has been the focus of different researches . The main aim is to lower the rate of cesarean section and undue hospitalization. Friedmans, Hendricks , and Philpotts Partographs and Nesheims regression equation are the results of such efforts. The advantage of an equation ov
30、er a partograph is its predictive value in determining obstructed labor in advance and on an individualized basis.,WHO partograph,Linear Regression Estimates the coefficients of the linear equation, involving one or more independent variables, that best predict the value of the dependent variable.Th
31、e two-variable model Y = A + B X,Materials and methods,230 Laboring women were interviewed and examined according to a checklist from April August 2004 .,The inclusion criteria were:,1-Singleton pregnancy 2- Vertex presentation 3- Gestational age 36-42 weeks 4- no medical or obstetric disease 5- Bis
32、hop score of 10-12 6- normal FHR 7- spontaneous initiation of labor 8- non elective cesarean section 9- no diagnosis of CPD,1-mothers height 2- maternal age 3- prepregnancy weight 4- maternal BMI 5- drugs used except oxytocin 6- 9interventions ( amniotomy c/s/vacuum/ enema or any other way of bowels
33、 preparation) 10- 12- Duration , intensity and frequency of labor pain (in the initial stages before oxcytocin administration),The independent variables were:,13-abnormal events like cord prolapse or fetal heart abnormality or occiput posterior delivery 14- occupation 15-31- lifestyle in terms of al
34、cohol consumption, smoking, exercise, meals, Consumption of grain , vegetables, fruit, dairy and type of dairy, meat ad meat products, fat and dressings , water, snacks , and score as the sum of items,The independent variables were:,Framingham Health Assessment Questionnaire is presented (though in
35、small font size) as a reference for a print. It can help provide an account of life style risk for health. Four items were changed based on Iranian pregnant women characteristics: Alcohol consumption smoking Exercise and type of dairy products,13.0 Consumption of alcoholHow often do you consume alco
36、hol?_1) Never drink_2) 2 days or less per week_3) 3 days per week_4) 4 or more days per week14.0 Number of alcoholic beveragesOn the days you drink, on the average how many drinks do you have?_1) Never drink_2) 1 to 2 drinks_3) 3 to 4 drinks_4) 5 or more drinks15.0 Caffeine How often do you consume
37、caffeine in your diet including coffee, tea, cola or chocolate?_1) Never_2) Occasionally but not every day_3) 1 to 3 servings daily_4) 3 to 5 servings daily_5) More than 5 servings daily16.0 Smoking statusIndicate which of the following best represents your current statusNOTE: Check all that apply._
38、1) Have never smoked_2) Quit smoking less than 5 years ago_3) Quit smoking more than 5 years ago_4) Smoke pipe or cigar_5) Smoke less than 1 pack of cigarettes per day_6) Smoke more than 1 pack of cigarettes per day,LIFESTYLE ITEMS,Exercise Program18.0 Exercise FrequencyOn the average, how many days
39、 per week do you exercise?_1) 3 or more days per week_2) Less than 3 days per week_3) No regular exercise program19.0 Proper stretchingDo you perform stretching prior to exercise?_1) Always_2) Sometimes_3) Never_4) Currently not exercising20.0 Warm-up and cool downDo you warm-up and cool-down after
40、exercising?_1) Always_2) Sometimes_3) Never,_4) Currently not exercising,Section E Nutrition Habits21.0 Daily MealsOn the average how many meals do you consume per day?_1) 3 meals with “healthy“ snacks_2) 3 meals_3) 2 meals or less_4) No regular eating pattern22.0 Consumption of grain/bread products
41、 On the average, indicate the type and amount of grain products you normally consume per day. NOTE: A serving is 1 sl. bread, 1/3 cup beans / peas, 1/3 cup oatmeal, rice or other grain products._1) Whole grains at least 6 to 11 servings per day_2) Whole grains 6 servings or fewer servings per day_3)
42、 Refined grains such as white bread/rolls/processed flour at least 6 to 11 servings per day_4) Refined grains such as white bread/rolls/processed flour 6 or lessservings per day_5) Rarely consume grain products,23.0 Consumption of vegetables On the average, how many servings of vegetables do you con
43、sume per day? Note: A serving is approximately 1 cup of raw or 1/2 cup of cooked._1) At least 3 to 5 servings per day_2) Less than 3 servings per day_3) Rarely consume vegetables24.0 Consumption of fruits On the average, how many servings of fruit do you consume per day? Note: A serving is approxima
44、tely 1 piece of fruit._1) At least 2 to 4 servings per day_2) Less than 2 servings_3) Hardly ever consume fruit25.0 Daily consumption of dairy products On the average, how many servings of dairy products do you consume per day? Note: A serving is approximately 1 cup of milk or 1 oz. of cheese._1) At
45、 least 2 servings per day_2) Less than 2 servings_3) Hardly ever consume dairy products26.0 Type of Dairy productsIndicate the type of dairy products you consume._1) Nonfat selections only_2) Both low fat and nonfat about the same_3) Low fat only_4) Usually high fat selections_5) Do not consume dair
46、y products27.0 Daily consumption of meats and meat productsIndicate the type of meat you normally consume._1) Do not consume meat or meat products_2) Consume less than 6 oz. of poultry or fish per day_3) Consume more than 6 oz. of poultry or fish per day_4) Consume less than 6 oz. of red meat per da
47、y_5) Consume more than 6 oz. of red meat per day28.0 Consumption of fats, dressings and spreads Indicate the type and number of servings of fat, dressings and spreads you consume each day.High fat examples: Butter, lard, and margarineLow fat examples: Non-fat or Low-fat salad dressing-mayonnaise-che
48、ese _1) Use low fat selections sparingly (less than 3 per day)_2) Use low fat selections frequently (3 or more per day) _3) Use both low fat and high fat about the same sparingly (3 or less)_4) Use high fat selections sparingly (less than 3 per day)_5) Use high fat selections (more than 3 per day),O
49、n the average, how many glasses of water do you consume per day? Note: A serving is one 8-oz. glass of water only; do not include coffee, soda or other beverages._1) At least 8 glasses per day_2) About 4 to 8 glasses per day_3) Less than 4 glasses per day_4) Seldom consume water30.0 Convenience and snack food consumption On the average how many times per day do you eat convenience foods or forms of fast food?_1) Never_2) Less than 1 time per day,
