Are promoted Premiership teams now more likely avoid relegation?

Not my usual article today, but I thought I'd post it as a follow up to a question I was asked earlier. "Are newly promoted teams to the English Premier League performing better in recent seasons than they used to?" In other words, are more of them staying up their first season after promotion from the Championship?

To investigate this I have considered the 21 Championship seasons from 1994/5 to 2014/15 and their corresponding Premiership season the year after, for which there were 20 teams playing. The table below shows the number of promoted teams (out of a possible 3) that were immediately relegated the following season. 1995 is excluded since there were only 2 teams promoted.

Clearly there is little discernible pattern to see here. The majority of seasons have seen at least 1 team relegated straight back down, with 7 out of 20 seasons seeing at least 2. On average 43.3% of teams promoted from the Championship are relegated from the Premiership the following season. Comparing the most recent 10 seasons with the previous 10, we can see that 12 teams have been re-relegated immediately, compared to 14. The difference is not statistically significant.

The next chart shows the Premiership finishing positions of each promoted team, including the 1st place, 2nd place and 3rd place, along with an overall average.

There is very little difference between each position. The overall average finishing position for a promoted team is 15.1, compared to 15.0, 14.9 and 15.7 for 1st place, 2nd place and 3rd place teams. There is no discernible statistically significant trend for any. To all intents and purposes, the data present a random walk. Evidently, despite the financial evolution of the Premier League over the past 20 season, it remains as hard as ever to keep your place amongst the elite of English football having joined the previous season.