Medical Statistics at a Glance pot

[...]... stages Formats for data entry There are a number of ways in which data can be entered and stored on a computer Most statistical packages allow you to enter data directly However, the limitation of this approach is that often you cannot move the data to another package A simple alternative is to store the data in either a spreadsheet or database package Unfortunately, their statistical procedures are... limited, and it will usually be necessary to output the data into a specialist statistical package to carry out analyses A more flexible approach is to have your data available as an ASCII or text file Once in an ASCII format, the data can be read by most packages ASCII format simply consists of rows of text that you can view on a computer screen Usually, each variable in the file is separated from... square of the units of the raw data Sensitive to outliers Inappropriate for skewed data Standard deviation Same advantages as the variance Units of measurement are the same as those of the raw data Easily interpreted Sensitive to outliers Inappropriate for skewed data The standard deviation is the square root of the variance In a sample of n observations, it is: We can think of the standard deviation... 'errors', or may be unexplainable random variation We measure the impact of variation in the data on the estimation of a population parameter by using the standard error (Topic 10) When the measurement of a variable is subject to considerable variation, estimates relating to that variable will be imprecise, with large standard errors Clearly, it is desirable to reduce the impact of variation as far as possible,... skewed data Only appropriate if the log transformation produces a symmetrical distribution Weighted mean Same advantages as the mean Ascribes relative importance to each observation Algebraically defined Weights must be known or estimated The geometric mean The arithmetic mean is an inappropriate summary measure of location if our data are skewed If the data are skewed to the right, we can produce a distribution... this method is that it takes twice as long to enter the data, which may have major cost or time implications Error checking Categorical data-It is relatively easy to check categorical data, as the responses for each variable can only take one of a number of limited values.Therefore, values that are not allowable must be errors Numerical data-Numerical data are often difficult to check but are prone to... reliable The reasons why data are missing should always be investigated-if missing data tend to cluster on a particular variable and/or in a particular sub-group of individuals, then it may indicate that the variable is not applicable or has never been measured for that group of individuals In the latter case, the group of individuals should be excluded from any analysis on that variable It may be that... the log data is approximately symmetrical, the geometric mean is similar to the median and less than the mean of the raw data (Fig 5.2) Advantages Describing data (2): the 'spread' Summarizing data If we are able to provide two summary measures of a continuous variable, one that gives an indication of the 'average' value and the other that describes the 'spread' of the observations, then we have condensed... information is collected on the same patient on more than one occasion It is important that there is some unique identifier (e.g a serial number) relating to the individual that will enable you to link all of the data from an individual in the study Categorical data Some statistical packages have problems dealing with nonnumerical data Therefore, you may need to assign numerical codes to categorical data... Data entry When you carry out any study you will almost always need to enter the data into a computer package Computers are invaluable for improving the accuracy and speed of data collection and analysis, making it easy to check for errors, producing graphical summaries of the data and generating new variables It is worth spending some time planning data entry-this may save considerable effort at later . Medical Statistics at a Glance is directed at undergraduate medical students, medical researchers, postgraduates in the biomedical disciplines and at. output the data into a specialist statistical package to carry out analyses. A more flexible approach is to have your data available as an ASCII or