Kiểm định giả thuyết "Đó có phải là do cơ hội, hay cái gì khác? thống kê có phát minh ra các xét nghiệm có ý nghĩa để đối phó với loại câu hỏi này. " (Freedman, Pisani, và Purves, 1997) Bước 5 trong quá trình DQO EPA dịch các câu hỏi rộng được xác định trong Bước 2 vào giả thuyết thống kê có thể kiểm chứng cụ thể. Ví dụ của các câu hỏi rộng có thể là như sau. • Có ô nhiễm tại trang web này đặt ra một nguy cơ cho sức khỏe và môi trường? • là xả phù hợp với các. | 4 C H A P T E R 3 Hypothesis Testing Was it due to chance or something else Statisticians have invented tests of significance to deal with this sort of question. Freedman Pisani and Purves 1997 Step 5 of EPA s DQO process translates the broad questions identified in Step 2 into specific testable statistical hypothesis. Examples of the broad questions might be the following. Does contamination at this site pose a risk to health and the environment Is the permitted discharge in compliance with applicable limitations Is the contaminant concentration significantly above background levels Have the remedial cleanup goals been achieved The corresponding statements that may be subject to statistical evaluation might be the following The median concentration of acrylonitrile in the upper foot of soil at this residential exposure unit is less than or equal to 5 mg kg The 30-day average effluent concentration of zinc if the wastewater discharge 4 from outfall 012 is less than or equal to 137 Mg l The geometric mean concentration of lead in the exposure unit is less than or equal to that found in site specific background soil The concentration of thorium in surface soil averaged over a 100-square-meter remedial unit is less than or equal to 10 picocuries per gram These specific statements which may be evaluated with a statistical test of significance are called the null hypothesis often symbolized by H0. It should be noted that all statistical tests of significance are designed to assess the strength of evidence against the null hypothesis. Francis Y. Edgeworth 1845-1926 first clearly exposed the notion of significance tests by considering Under what circumstances does a difference in calculated figures correspond to a difference of fact Moore and McCabe 1993 p. 449 Stigler 1986 p. 308 . In other words under what circumstances is an observed outcome significant. These circumstances occur when the outcome calculated from the available evidence the observed data is not likely to
