OTTAWA -- While Statistics Canada reports the national crime rate is down, some observers warn the numbers don't tell the whole story. In its annual police-reported crime survey, Statistics Canada noted a drop in most types of offences across the country in 2011. This follows a longtime trend in Canada, where crime has been dropping annually since its peak in 1991.

Fewer attempted murders, major assaults, robberies, break-ins and vehicle thefts were seen in 2011 than 2010.

But cases of homicides, sexual violence against children, child porn, criminal harassment, impaired driving and most drug offences all rose.

The homicide rate rose by 7%, Statistics Canada noted. Police reported 598 homicides in 2011 -- 44 more than in 2010. However, homicides have been declining in general since the rate peaked during the mid-1970s.

The most significant increases were in child porn offences, which rose 40% - the highest in any category. But Statistics Canada attributes this to better police work, rather than a spike in the number of people accessing child porn.

"Fluctuations in the rate of child pornography are likely reflective of police-based programs and initiatives targeting this particular offence," the agency said.

Sexual offences against children were also up 3%, with the rate of luring a minor via a computer up 10%.

Data for the survey are based solely on information "that's brought to police attention," Shannon Brennan of Statistics Canada said.

Scott Newark, former Crown attorney who has written about the skewed nature of the survey, said using only police-reported crimes is part of the problem.

"Two-thirds of crimes surveyed are not reported (to police), according to (Statistics Canada's) victimization survey," Newark said.

Statistics Canada's most recent 2010 victimization report found more than one in four Canadians - 7.4 million people - said they had been victims of crime, with a whopping 69% of them not alerting police. Fully 88% of sex assaults went unreported. More than eight million Canadians said they believed crime increased in their neighbourhoods over the past five years.

The survey also reported the crime severity index - which measures the severity of crimes - fell by 6% from 2010 to 2011.

Newark calls the crime severity index "absurd" and explained it only counts "the most serious offence in multiple offence incidents which, by definition, minimizes reporting of repeat offender activity."