One Tailed and Two Tailed Tests
The critical region ( or the region of rejection) which is generally 5 per cent is kept on both sides of the normal distribution in a two tailed test. It means that 2.5 per cent of the critical is on the extreme left of the normal curve and 2.5 percent on the extreme right. The middle 95 % is the acceptance region in a single tail test the 5 per cent area would be either on the extreme left of the normal curve or on the extreme right. The remaining 95 percent area would be the acceptance region.
Two tailed test is applied when the null hypothesis is that mean weight of the undergraduate male students is 120 pounds and the alternate hypothesis is that it is not 120 pounds. In such a situation the actual value of the population mean or maybe more than 120 pounds or less than 120 pounds. In such situation a two tailed is appropriate.