http://www.snopes.com/crime/statistics/ausguns.asp
In the specific case offered here, context is the most important factor. The piece quoted above leads the reader to believe that much of the Australian citizenry owned handguns until their ownership was made illegal and all firearms owned by "law-abiding citizens" were collected by the government through a buy-back program in 1997. This is not so. Australian citizens do not (and never did) have a constitutional right to own firearms — even before the 1997 buyback program, handgun ownership in Australia was restricted to certain groups, such as those needing weapons for occupational reasons, members of approved sporting clubs, hunters, and collectors. Moreover, the 1997 buyback program did not take away all the guns owned by these groups; only some types of firearms (primarily semi-automatic and pump-action weapons) were banned. And even with the ban in effect, those who can demonstrate a legitimate need to possess prohibited categories of firearms can petition for exemptions from the law.
Given this context, any claims based on statistics (even accurate ones) which posit a cause-and-effect relationship between the gun buyback program and increased crime rates because "criminals now are guaranteed that their prey is unarmed" are automatically suspect, since the average Australian citizen didn't own firearms even before the buyback. But beyond that, most of the statistics offered here are misleading and present only "first year results" where long-term trends need to be considered in order to draw valid cause-and-effect conclusions.
For example, the first entry states that "Homicides are up 3.2%." This statistic is misleading because it reflects only the absolute number of homicides rather than the homicide rate. (A country with a rapidly-growing population, for example, might experience a higher number of crimes even while its overall crime rate decreased.) An examination of statistics from the Australian Institute of Criminology (AIC) reveals that the overall homicide rate in Australia has changed little over the past decade and actually dipped slightly after the 1997 gun buy-back program. (The chart found at this link also demonstrates how easily statistics based on small sample sizes can mislead, as when the homicide rate in Tasmania increased nearly eight-fold in one year based on a single incident in which 35 people were killed.)
Then we have the claim that "In the state of Victoria alone, homicides with firearms are now up 300 percent." This is another example of how misleading statistics can be when the underlying numbers are not provided: Victoria, a state with a population of over four-and-a-half million people in 1997, experienced 7 firearm-related homicides in 1996 and 19 firearm-related homicides in 1997 (an increase of 171%, not 300%). An additional twelve homicides amongst a population of 4.5 million is not statistically significant, nor does this single-year statistic adequately reflect long-term trends. Moreover, the opening paragraph mixes two very different types of statistics — number of homicides vs. percentage of homicides committed with firearms. In the latter case, it should be noted that the Australia-wide percentage of homicides committed with firearms is now lower than it was before the gun buy-back program, and lower than it has been at any point during the past ten years. (In the former case, the absolute number of firearm homicides in Australia in 1998-99 was the lowest in the past ten years.)
