TM vs Raid difficulty

Out of 13 level 1 and 2 raids, I received 0 TMs. Out of 2 level 4 raids, I received 0 TMs.

People told me they had gotten at least 1 TM at level 1 and 2 raids. A couple of people got as many as 3 (that I heard) at the level 4 raids.

win level 2 raid battle once, got no TMs
win level 4 raid battle twice, got 2 TMs at the 2nd time

First raid ever, level 2 (Muk) and I got my first fast TM so I think it's totally random.

11 raids, 2 tm of each:
1 lvl 2 raid - 1 fast and 1 charge tm
1 lvl 3 - 1 fast tm
1 lvl 4 - 1 charge tm

1 lvl 3 raid - 0 tm
7 lvl 1-2 raids - 0 tm

I also did 13 raids yesterday. (I don't mind spending the money, I can afford it, and PoGo is my favorite pasttime...don't judge)

Got a total of 5 Tms (all used already...I hope they keep coming!)

I didn't follow closely enough, but I definitely got TMs with both level 1 raids and level 4. I was somehow expecting to get more out of the Level 4 raids, so I was disappointed on 2 of them that I didn't get a TM.

Only once did I get 2 TMs on one raid, and that was a level 3.

Got 2xCharge move Tm yesterday on level 3 Arcanine raid.

Got 1xCharge move Tm today on level 3 Alakazam raid.

I think it is random but the more damage you do the better chances of getting one, just a guess, because both of my raids have been done only with 2 players, me and another one.

7 raids = No TMs