Why it’s important to consider a maximum Conversion Rate!

Conversion Rates (CR) have been used in the research to highlight how later born players (Q3 & Q4) are more likely to transition to the next step in a development pathway or indeed to reach international levels. However, CRs have some drawbacks.

Whenever a Birth Quarter (BQ) dominates the others and a (de)selection point means a significant reduction in the overall numbers, then the more dominant a BQ is the lower it’s CR is likely to be relative to the other BQs.

In this CR example 10 players are selected from a cohort of 100 players who are split into BQ thus:

Q1 50, Q2 30, Q3 15, Q4 5

If we try to fill the 10 available spaces from just one BQ then the maximum CR% for each BQ would be 20, 33, 67, 100. (Obviously if all 5 Q4 are selected we would need 5 from other BQs.)

The only outcome where Q1 could have a CR higher than Q4 is when there are zero Q4s. If just 1 Q4 is selected then that is a CR of 20%. In this instance even if all the remaining players were all Q1, the CR% for Q1 would only be 18%. For Q1:Q4 at 8:2 CR is then 16% & 40% respectively and so on.

CRs for uneven groups cannot be compared. Each group has its own maximum CR and different values for every player selected. In this example each Q1 player adds just 2% but each Q4 player 20%. They are different scales.

Thus, be very careful when comparing Conversion Rates with a starting imbalance in the cohort.

Other factors are involved in the Underdog Effect, other than challenge, such as a natural Selection Concentration Effect.