Null Hypothesis Significance Testing: What you should know (Part 2)

Substantive or Conceptual Alternative

The conceptual or scientific alternative is that which is inferred by a scientist once the null hypothesis is rejected. It is an explanation or theory that serves as the ‘reason’ that the null was rejected. Theoretically, there could be countless explanations for why a null is rejected.

It is entirely possible to assume an incorrect conceptual alternative, as illustrated by the example below:

Example

The miasma theory states that miasmas are poisonous emanations from rotting carcasses/ vegetation or molds, and invisible dust particles inside dwellings. They were once believed to enter the body and cause diseases like tuberculosis, malaria, and cholera. Before the discovery of microbes, this offered a popular explanation for disease occurrence.

For many years, it was believed that cholera was caused by miasmas emanating from rivers. Miasmas were thought to be denser than fresh air, and supposedly had the greatest effect at sea level. This gave rise to the belief that living at altitude was beneficial for disease prevention. In this case, scientists comparing samples from two populations (those living at sea level and those who do not) could easily have rejected the null hypothesis that the rates of cholera were equal in the two populations. Then they would have inferred the statistical alternative, that the rates of cholera were higher in the sea-level population. Researchers could then infer a conceptual alternative- living at sea-level causes cholera. However, without experimental control built into the study, the conceptual alternative is no more than a convenient explanation promoted by the researchers, and is prone to bias (due to prejudice of the researchers).

In fact, William Farr firmly stated in his annual report on vital statistics in Great Britain in 1852 that the inverse association of cholera mortality with elevation above sea level confirmed the miasma theory as its cause. Using logic and reasoning, Farr rejected John Snow’s argument that cholera was caused by contaminated drinking water.

Although the miasma theory was soon disproved as the cause for cholera, it was partially sustained as an explanation for malaria for several years.

1 thought on “Null Hypothesis Significance Testing: What you should know (Part 2)

  1. Pingback: Null Hypothesis Significance Testing: What you should know (Part 3) | communitymedicine4all

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