The 2.74 in your example is the average increase. The plus or minus value of 0.28

kg is *either* the standard deviation or the standard error. You cannot tell which unless

they say. If it’s the standard deviation,

this means that (approximately) 65% of cases

fell within 0.28 kg one way or the other

of the average, approximately 95% fell within

0.56 kg (twice that), etc.

If it’s the standard error, this is looser

and the significance depends on the sample size. So an 0.28 kg standard deviation is

pretty consistent results, whereas 0.28 kg

standard error might be pretty inconsistent.

The p value is the probability that an average

result as large as this could have occurred

just by chance, not from actual cause. In this case, it’s only a chance of 0.0002, or one chance in 5000. (Hypothetically, if it was found

that a few men in the control, untreated group gained muscle mass without receiving testosterone, it could be that the treated group all or mostly were composed of men who happened to be like that.)