# Point estimate of proportion

#### hjk

##### New Member
A study was conducted at the University of Waterloo on the impact characteristics of football helmets used in competitive highschool programs. There were three types of helmets considered, classified according to liner type: suspension, padded-suspension, and padded. In the study, a measurement called the Gadd Severity Index (GSI) was obtained on each helmet using a standardized impact test. A helmet was deemed to have failed if the GSI was greater than 1200. Of the 81 helmets tested 33 failed the GSI 1200 criterion. Assuming the suspension helmets tested were selected at random, calculate the point estimate of the proportion of suspension helmets that fail, and the standard error of the estimate.

Can I get some theory links that can help me solve this question? I don't know how to convert the entire population proportion of 33/81 to the particular category of suspension helmets.

#### katxt

##### Active Member
Perhaps the 33/81 is for suspension helmets alone.

#### joeb33050

##### Member
"I don't know how to convert the entire population proportion of 33/81 to the particular category of suspension helmets."
You need to know n tested and n failed by susp./susp&pad/ pad, for the 81 tested and 33 failed. Six numbers. No links, theories or trick-cyclist math will "convert".