>>16733830 (OP)in the first year 2 more people entered your tribe
in the second year, 2 more people entered your tribe
in the third year, 2 more people entered your tribe
every year, 2 more people enter your tribe
the change in your tribe is the same every year
this is a constant rate of change
contrast with
in the first year, 2 people entered your tribe
in the second year, 4 people entered your tribe
in the third year, 6 people entered your tribe
the amount of people entering your tribe every year is increasing
this is a positive rate of change
in the first year 2 people joined your tribe
in the second year, 1 person joined your tribe
in the third year, nobody joined or entered your tribe
in the fourth year, 1 person left your tribe
in the fifth year, 2 people left your tribe
every year, fewer people join your tribe or more people leave your tribe
this is a negative rate of change