STATISTICAL METHODS

HOW TO WRITE A SCIENTIFIC PAPER

Medical StatisticsProf.Dr.Amany Rashad Aboel-Seoud Community Medicine Department

Zagazig university

Definition of statistics

• It is the science and art of dealing with numbers.

• Used for collection, summarization, presentation and analysis of data to get information based on objective basis (un-biased).

Uses of statistics

• Descriptive information for any population

• Prove association between variables• Prove relation between risk and disease• Compare two studied groups (or more)• Evaluate health programs & services

Medical Statistics

population

Inferential Statistics

• Put a hypothesis X = Y H0 or X >Y H1 or Y>X H2• Collect, summarize data• Test your hypothesis using tests of significance: Comparison of mean values : t , paired t test & ANOVA (used for numeric continuous data) Finding relations between different variables using

Correlation & regression tests

Correlation test

To find a relation between 2/more variables in direction & strength (one is dependent = response. It is plotted on the y axis) &(the other/s is independent = explanatory or risk. It is plotted on the x axis)

• Correlation does not mean causation.• Spurious correlation: significant statistically but

insignificant clinically

Types of correlation

+ve

-ve

No

Coefficient of correlation “r” ranges from 0 to 1 It is either +ve or -ve in direction

(r=0.5 p=0.02), (r=- 0.6,p=0.01) (r= 0.1,p=0.98)

Coefficient of determination R 2 : to quantify the variation of one variable that is contributed to the other variable.

Types of correlation: I) single (simple) & multipleII) Pearson : numeric, normally distributed, linear Spearman : ordinal, non linear, not normally distributed

Regression analysis

To predict a dependent variable from another known variable (s).

• Linear: dependent = intercept +/- b coefficient x independent variable

e.g. birth wt = y +/- b x gestational age = 0.21 + 5 x 36• Multiple e.g. Birth wt= y +/- b1*gest+/- B2*HC

Wilcoxon test, Mann Whitney test

Analysis of qualitative data

(1) Chi squared test : to find significant relation between 2 variables or order distributions or categorical data.

(2) Difference between proportions (z test) as t test but use percentage instead of mean

values

Thank you