Basic biostatistics for post-graduate students PMC

It may be binominal distribution or Poisson distribution. In binominal distribution, event can have only one of two possible outcomes such as yes/no, positive/negative, survival/death, and smokers/non-smokers. When distribution of data is non-Gaussian, different test like Wilcoxon, Mann-Whitney, Kruskal-Wallis, and Friedman test can be applied depending on nature of data. Even after calculating the mean, it is necessary to have some index of variability among the data.

Summary measures of variability of individuals are further needed to be tested for reliability of statistics based on samples from population variability of individual. Median is an average, which is obtained by getting middle values of a set of data arranged or ordered from lowest to the highest . In this process, 50% of the population has the value smaller than and 50% of samples have the value larger than median.

• • If we repeat many times an experiment, when obtained expected result, it is divided between number of experiments to know the probability.
• Learn advanced approaches to genomic visualization, reproducible analysis, data architecture, and exploration of cloud-scale…
• Recall from the discussion about sampling that when we say that a random sample represents the population well we mean that there is no inherent bias in this sampling technique.

Hence, in such situation, we will have to make the decision which is more precise while selecting the appropriate test. Statistical tests can be divided into parametric and non-parametric tests. If variables follow normal distribution, data can be subjected to parametric test, and for non-Gaussian distribution, we should apply non-parametric test. Statistical test should be decided at the start of the study. Following are the different parametric test used in analysis of various types of data.

Probability Distribution:

We often want to estimate the chance that an event will occur. In this section, we definedprobabilityas thelikelihoodor chance that something will occur and introduced the basicnotationof probability such as P. The closer the probability is to 0, the less likely the event is to occur. The closer the probability is to 1, the more likely the event is to occur. After doing this experiment, an important question naturally comes to mind.How would we know if the coin was not fair? Certainly, classical probability methods would never be able to answer this question.

Statistical methods are important to draw valid conclusions from the obtained data. This article provides background information related to fundamental methods and techniques in biostatistics for the use of postgraduate students. Main focus is given to types of data, measurement of central variations and basic tests, which are useful for analysis of different types of observations. Few parameters like normal distribution, calculation of sample size, level of significance, null hypothesis, indices of variability, and different test are explained in detail by giving suitable examples.

Relative Frequency

The shape of https://1investing.in/ distribution is unimodel, symmetrical and the ends of the curve tail off to the base. When two events are so related that the occurrence of one prevents the occurrence of the other or vice-versa in a trial, they are said to be mutually exclusive events. For example, tossing of a coin is a trial which provides an equal opportunity for the head or tail to turn up and in the trial only one, either head or tail can occur but not both. To estimate the probability of event A, written P, we may repeat the random experiment many times and count the number of times event A occurs.

The concept of probability in biostatistics is of paramount importance in statistics as it provides the basis for all the tests of significance. This indicates that the number of different combinations increases with the increase of the number of independent events. Increase in the number of independent events by one will double the number of possible combinations. Table 32.1 Probability of different combinations of head and tail of coin A and coin B tossed either simultaneously or separately. If a cubical die having six sides or faces mentioned 1,2,3,4,5 and 6 is rolled, any one of the 6 different faces may turn up.

Using these guidelines, we are confident enough that postgraduate students will be able to classify distribution of data along with application of proper test. Information is also given regarding various free software programs and websites useful for calculations of statistics. Thus, postgraduate students will be benefitted in both ways whether they opt for academics or for industry.

Types of Distribution

But sampling many people at random, and finding the relative frequency of blood type O occurring, provides an adequate estimate. Statistical methods are necessary to draw valid conclusion from the data. This article provides a background information, and an attempt is made to highlight the basic principles of statistical techniques and methods for the use of postgraduate students. When we want to compare two sets of unpaired or paired data, the student’s ‘t’ test is applied.

The CDC estimates that in 2011, 8.3% of the U.S. population have diabetes. In other words, the CDC estimates the prevalence of diabetes to be 8.3% in the U.S. Unfortunately, when looking at a particular sample , we will never know how much it differs from the population. Estimate population values, such as the population mean or population proportion. If you have found these materials helpful, DONATE by clicking on the “MAKE A GIFT” link below or at the top of the page!

Three different combinations of one head and two tails- . Three different combinations of 2 head and one tail- . As a graph of the distribution, which looks and works much like a histogram of observed data. As a mathematical equation that gives the chance that a fluctuation will be of a certain magnitude.

However, we can control how good this estimate is by the number of times we repeat the random experiment. The more repetitions that are performed, the closer therelative frequencygets to thetrue probabilityof the event. The mean hemoglobin of newborn is observed to be 10.5 (1.4) in pregnant mother of low socioeconomic group. It was decided to carry out a study to decide whether iron and folic acid supplementation would increase hemoglobin level of newborn. There will be two groups, one with supplementation and other without supplementation. Minimum difference expected between the two groups is taken as 1.0 with 0.05 level of significance and power as 90%.

Biostatistics

Biostatistics covers applications and contributions not only from health, medicines and, nutrition but also from fields such as genetics, biology, epidemiology, and many others. Biostatistics mainly consists of various steps like generation of hypothesis, collection of data, and application of statistical analysis. To begin with, readers should know about the data obtained during the experiment, its distribution, and its analysis to draw a valid conclusion from the experiment.

This distribution of values is the probability mass function. The probability of a one fatal airline accident in a year exactly on 20.1 is practically zero , so we can get the probability of a range of values around the point as our answer. This test is used when data are not normally distributed in a paired design. It analyses only the difference between the paired measurements for each subject. If P value is small, we can reject the idea that the difference is coincidence and conclude that the populations have different medians.

Following are the non-parametric tests used for analysis of different types of data. Various medical journals use mean and SEM to describe variability within the sample. The SEM is a measure of precision for estimated population mean, whereas SD is a measure of data variability around mean of a sample of population.

Discrete probability

Power of study is very important while calculation of sample size. Power of study can be calculated after completion of study called as posteriori power calculation. This is very important to know whether study had enough power to pick up the difference if it existed. Any study to be scientifically sound should have at least 80% power.

When two or more events are so related that the occurrence of one does not affect the possibility of the occurrence of remaining event, they are said to be independent events. For example, when two coins A and B are tossed together or separately, the head or tail of coin A does not affect the possibility of the occurrence of head or tail of coin B. Thus, turning up of head or tail of coin A is independent of that of coin B. When two mutually exclusive events are such that the possibility of occurrence of one event is neither less nor more than the possibility for the occurrence of other event, they are said to be equally likely events.

The probability that at birth, a human baby’s sex will be male about 1/2 or 50%. This is an empirical probability based on millions of observations. Changes in technology, and ethical standards notwithstanding, the probability will remain the same. Ludbrook J. The presentation of statistics in Clinical and Experimental Pharmacology and Physiology.