Summary: From the few papers I've looked at, microtransaction-based games tend to work as suspected/designed. That is, games which rely on frustration to get the player to spend money (like Candy Crush) tend to obtain money from players with low tolerance for frustration; games which are more related to gambling (like "social casino" games) tend to get money from players who score high on gambling-problem scales and so forth. There are probably not enough high spenders in such games to reflect their behavior in the (unweighted) average player. There's one cluster-analysis paper suggesting that the motivations of the high-spenders (and thus possibly other parts of their psychological profile) are different than those of the average spender. But I think the research on that is too limited to draw firm conclusions on this aspect.
I found one paper specifically about Candy Crush, "Self-Control in Casual Games:
The relationship between Candy Crush Saga™ players’ in-app purchases and self-control":
Our study reveals that the amount players spend on in-app purchases
is correlated with lower levels of self-control. On the other
hand, purchases and self-control levels were not significantly
correlated with the amount of time people play, game addiction,
or problem video game playing.
So in a game where the microtransaction are mainly a way to speed-up the game (a fairly typical freemium design), the people that pay are those with poor self-control who get crushed by the game's non-paying pace and repetitiveness. Self-control was measured in this paper in a uniform manner using the (highly cited/used) Self-Control Scale (SCS) from Tangney et al.
The authors also quote a couple of free-form responses for additional insight/confirmation:
I'm trying really hard not to spend money on games. I did it
a few times after being stuck for weeks because I was frustrated
but I'm trying not to do it again.
I am feeling really frustrated because I am having trouble
getting past this level. I know that if I buy the fish boosters,
then I would have an easier time of getting past this level. I
am seriously contemplating hitting the buy now option on my
ipad to purchase the boosters. I get frustrated with myself
and disgusted at the game turn it off, and then go to play
farm hero saga instead, which is similar to candy crush but it
is a lot less difficult to spend money on it because it is easier
There's a more recent (2016) paper "Who Spends Money to Play for Free? Identifying Who Makes Micro-transactions on Social Casino Games (and Why)." limtited alas to "social casino" games like Slotomania.
Results showed that social casino gamers who engaged in micro-transactions reported significantly higher levels of impulsivity, reward sensitivity and problem gambling severity, but not competitiveness. In terms of motivation to make micro-transactions, desire to extend play was endorsed most frequently, followed by a desire to access additional features, chasing lost credits, and to speed up play. Lastly, among participants who made micro-transactions, reward sensitivity predicted making micro-transactions to chase lost credits. These results suggest the personality make-up of social casino gamers is important to understand who is likely to make micro-transactions as well as their motivation to do so-information that could prove useful for regulation of the industry.
And in numerical detail, the difference between spenders and non-spenders:
The results in this study confirm gambling-like addiction behavior as predictor for spending. The results may not fully generalized to other types of microtransaction games (e.g. where players more obviously compete with each other), but some seem consistent with the designer's intention in this particular game. I had never heard of "buying back your virtual credits" before, but apparently people spend money on that too. Perhaps a clever (or--depending on your point of view--unscrupulous) way to tap into loss aversion. Or maybe just a way of extending play in this type of game.
The authors were quite reserved in their abstract; the breakdown of motives for various microtransaction incentives was close to statistical significance in quite a few other cases, e.g. impulsivity predicting the need to speed up the game had p=0.07; perhaps a better powered study would find some of these significant as well.
Some reference links for the measures used: PSGI, BIS-Brief for impulsivity, Smither and Houston's Competitiveness Index, whereas
Reward sensitivity was measured using two face valid items anchored at 1 (strongly
disagree) and 7 (strongly agree), ‘‘I play social casino games in order to win large sums of
virtual credits’’ and ‘‘I don’t find social casino games to be rewarding [reverse coded].’’
Higher scores indicated greater sensitivity to rewards.
And there's yet another 2016 also on "social casino" games (with a similar title too!): "Who Pays to Play Freemium Games? The Profiles and Motivations of Players Who Make Purchases Within Social Casino Games", which did a cluster analysis to find that:
A cluster analysis revealed distinct subgroups of paying players; these included more frequent moderate spenders who made purchases to avoid waiting for credits and to give gifts to friends as well as less frequent high spenders who made purchases to increase the entertainment value of the game.
Of note is that there was no statistical difference in income or education between these groups. But these groups were still a substantial proportion of the sample; total sample was 521; of these 261 had ever made a purchase and the two aforementioned clusters had 67 (moderate but frequent) and 52 (high but infrequent) spenders. I think neither of these clusters captured the actual "whales" who are probably an even smaller group.
There are more concrete numbers from the industry itself, but these are not in peer-reviewed publications. According to a Tapjoy report discussed in Adweek:
Whales, defined as the top 10% of an app's spenders, account for 70% of the app's revenue from in-app purchases and for 59% of its total revenue (which additionally includes advertising). Whales "make approximately 7.4 in-app purchases per month, for a median average revenue per paying user (ARPPU) of $335."
The rest of paying players make 1.75 in-app purchases per month, and have a median ARPPU of $17.94. But in contrast to this substantial monetary difference, the time spent in game is not that different: a median of 33 days compared to 40 days for whales.
Ad-tapping customers had an ARPPU of only $3.38.
91% of users were non-spending.
It's also interesting that spenders aren't that impulsive with their first purchase; the (average or median?) "time for spenders to make their first in-app payment is 16.3 days". This was based on Tapjoy’s "Personalized Monetization Platform", so it's presumably aggregate across multiple types of games.
The reason why I detailed these is that the clusters from the previously mentioned academic study don't quite mesh with this industry-reported data. So I suspect there may be substantial variability depending on the game, how you cluster the data etc.