Reporting SNR

I'm playing around with the data from two months I downloaded from here. At present, I'm just familiarising myself with the stuff. Here's a table of the mean signal strength reported by Reporter. It varies hugely, and it might be interesting to investigate why. I have cut out those reporters with less than 100 entries.

Here are the top few in August 2018.

Reporter/Average report dBm/Number of reports :

ZL3PX 11.34375 160
F1EYG/B 5.960018815 4252
VE3KU 4.329485996 6498
VK3JL 2.895184136 353
E29EKF 2.684210526 133
PA0SLT/1 2.20610687 1048
KJ6MKI/V 2.023553965 3354
7L1RLL1 2.017272186 3358
JA5FP 0.916013438 2679
I1DDS 0.627906977 129
ZL2IT/1 0.461734694 392
LA9LT -0.879310345 174
N1CSR -1.578688525 610
VK2IJM -2.28025912 2933
NU6O/RX -2.457537854 1519
ZS6SRL -2.462962963 378
W6GJB -2.732984293 382
VK3MHY -3.070809249 692
2E0VWW -3.16025641 156
DL3OH -3.644388398 793
DK5UY -3.649019608 1020
DK2SAM -3.955599735 3018
W0LEN -4.201923077 208
VK2KCM -4.55390625 1280
VK5BC -4.579831933 119
WINSWL -4.671708683 3570
N1HO -4.924401914 4180
KJ6MKI/H -5.151761919 6754
E20ZFD -5.18902439 164
VK5ZK -5.386792453 106

....and the bottom 30:

DG2HSI -23.33939394 165
OX3HI -23.40909091 418
ZS6PAJ -23.4375 112
W6TRO -23.45 140
ZS6RAS -23.47440273 293
R3AHC -23.48214286 168
K0GRT -23.49004975 402
SWL/K -23.51651982 908
9Z4FV -23.52317881 151
K6FYY -23.5477707 157
KK4UNE -23.56825397 315
DC0DX/MW1 -23.60629921 381
KL4IU -23.63691684 493
K6GOG -23.7037037 135
ZS1LCD -23.76816609 289
AA7XC -23.97026432 908
WA4269SWL -24.0450237 422
W0JW -24.19958093 1909
LB1TI -24.21186441 118
I55387FI -24.2300885 226
AF5WW -24.27755213 3693
G4HZW -24.49683544 316
N3IZN/R1 -24.67723343 347
VA7JX -24.72975078 1284
DJ8SR -24.92333223 3013
VK4TDI -25.04407295 1316
W3BRB -25.38715953 514
WB8AM -25.84210526 171
K8OK -25.98039216 153
N9JL -26.31558935 1052
N5EKF -26.41935484 124