The hypothesis which is to be tested is called null hypothesis.It is denoted by. It is a starting point in the investigations. A statement which we hope will be rejected is taken as a hypothesis. Modern approach is different. Today any hypothesis we wish to test is called null hypothesis and is denoted by. In this book we shall follow the old convention. Any hypothesis will be called null hypothesis only when we hope to reject it. Thus the null hypothesis is framed for possible rejection. Tall fathers have tall children. We shall assume that tall fathers do not have tall children. This will be considered as null hypothesis and will be denoted by. We are hoping that will be rejected on the basis of sample data. Use of coffee increases chances of heart attack. To start with we shall assume that heart attack has no link with the use .of coffee. This will be taken as and we hope it will be rejected by the sample data.