Question

A team of visiting polio eradication workers were informed during their orientation session that population-wide studies done in their host country showed that the risk of polio in villages of that country was strongly epidemiologically associated with the village’s economic/human development circumstances, which ranged greatly from village to village.  In some villages, residents lived in hand-constructed huts with no running water, no latrines or sewage disposal areas, and no electricity.  In other places, residents lived in wooden or adobe homes which, though modest by Western standards, had all of the above services in place and whose street side craft shops and food markets did a brisk business, catering both to locals and visitors.

Knowing this information, the team went into several villages and attempted to assign a “human development rating” to each family.  This was based on that family’s income situation, access to running water, access to elementary school for their children, and the condition of the home. To their surprise, they found that families in all the villages had no difference in polio risk based on the family’s human development rating.

Answer 1

Several reasons are possible for this contradictory results. One is the time gap between the population - wide studies and the study conducted by the polio eradication team. So, even if we assume that both the studies are conducted in a similar way by applying the same statistical procedures and methods and the study of polio eradication team is unbiased and the sample represents the population, the time gap may be the reason when considerable changes have taken place and thus, lead to no significant difference in polio risk based on the family’s human development rating even though the difference existed previously when pupulation - wide studies were conducted.

Now, the other reasons possible are the methods and procedures applied in both studies might be different that lead to the contradictory conclusions. And the sample of several villages may not be the representative of the entire population of interest.