In the hypothesis testing approach of Jerzy Neyman and Egon Pearson, a null hypothesis is contrasted with an alternative hypothesis, and the two hypotheses are distinguished on the basis of data, with certain error rates. Proponents of each approach criticize the other approach.
In geography, relief refers to the highest and lowest elevation points in an area. Mountains and ridges are typically the highest elevation points, while valleys and other low-lying areas are the lowest. Relief is essential to understanding the topography of an area.
Mountains are landforms that are raised steeply, forming peaks, above the surrounding terrain. Mountains are much steeper and higher than hills. Most mountains are formed by movements in the earth's crust. The height of a mountain is usually measured in meters above the sea-level. Mountains cover nearly one-quarter of Earth's land mass, and are source of most of the world's rivers.