Thống kê là tất cả về rút ra kết luận từ dữ liệu, và đã có nhiều hoạt động này trong các chương trước của cuốn sách này. Mục đích của chương này là xem xét chặt chẽ và nghiêm trọng hơn các phương pháp được sử dụng để rút ra kết luận. Khá nhiều chủ đề được xem xét, bao gồm cả một số khá quan trọng và thường nhận được sự quan tâm tương đối ít trong các văn bản thống kê. . | CHAPTER 4 Drawing Conclusions from Data Introduction Statistics is all about drawing conclusions from data and there has been much of this activity in the earlier chapters of this book. The purpose of the present chapter is to look more closely and critically at the methods that are used for drawing conclusions. Quite a variety of topics are considered including some which are rather important and yet often receive relatively little attention in statistics texts. These include the difference between observational and experimental studies the difference between inference based on the random sampling design used to collect data and inference based on the assumption of a particular model for the data criticisms that have been raised about the excessive use of significance tests the use of computer-intensive methods of randomization and bootstrapping instead of more conventional methods the avoidance of pseudoreplication the use of sampling methods where sample units have different probabilities of selection the problem of multiple testing meta-analysis methods for combining the results from different studies and the use of Bayesian inference which is currently receiving a great deal of attention. Observational and Experimental Studies When considering the nature of empirical studies there is an important distinction between observational and experimental studies. With observational studies data are collected by observing populations in a passive manner that as much as possible will not change the ongoing processes. For example samples of animals might be collected to estimate the proportions in different age classes or the sex ratio. On the other hand experimental studies are usually thought of as involving the collection of data with some manipulation of variables that is assumed to affect population parameters keeping other variables constant as far as possible. An example of this type would be a study where some animals are removed from an area to see .
