医学研究中的统计分析（一）. Statistical Analysis in medical research. Preface Key Concepts In Statistics The Common Statistical Methods Of Measurement Data. Main Content.
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Statistical Analysis in medical research
Medical statistics is an science which combines theory of statistics with medical science. It is indispensable for us to conduct medical research.
(a). Continuous variables or interval data
e.g. age , weight , height , BMI
(b). Discrete variables
e.g. the number of patients, newbornsKey Concepts
2. Categoricalvariables (nominal scale、 unordered categories)( Enumeration Data)
Racial-ethnic group (white, black, others)
sex(male or female)
3. Ranked (ordinal) variables （rank data）
Anxiety, stress, (high, medium, low)
Mental impairment (none, mild, moderate, severe)
interval > ordinal > nominalKey Concepts
1. Populations :a collection of similar people , observations ,or measurements , in which certain subjects can be sampled to infer a property or attribute of population.
Parameter：Numerical summary of the population. Parameters are unknown usually .
2. Samples : Subjects are selected from a population so that each individual has an equal chance of being selected .
Statistic：Numerical summary of the sampleKey Concepts
3. Simple random sample: In a sample survey, each possible sample of size n has same chance of being selected.
Use “random number tables” or statistical software that can
generate random numbers.Key Concepts
A probability provides a quantitative description of the likely occurrence of a particular event.
Probability is conventionally expressed on a scale from 0 to 1; a rare event has a probability close to 0, a very common event has a probability close to 1.
The probability of getting a value of the test statistic as extreme as or more extreme than that observed by chance alone , if the null hypothesis is true.Key Concepts
The P-value is compared to the actual significance level of the test ,and if it is smaller ,the result is statistically significant.
The most widely accepted significance level is 0.05, and the test is said to be “significant at the .05 level” if the P-value ≤ 0.05.
The smaller the P-value, the stronger the evidence against H0 , exact P-value should be reported.Key Concepts
1)Statistics used to answer questions concerning differences,
2)Statistics used to answer questions concerning associations,
3)Statistics used to answer questions concerning predictions
1) Measurement Data
2) Enumeration Data
3) rank data
1)( approx. )normal distribution
2)skewed distribution (positively or negatively)
No segmentation of data into groups
Segmentation of data into groups
Discrete or continuous data
Popular in Epidemiologic Studies
Useful for presenting comparative data graphically
Commonly reported in studies to provide an estimate of the precision of the mean.