Bias: Identify What Can Go Wrong — Worked Solutions

The scale systematically inflates recorded weights, so means computed from it tend to be larger than the true population mean. A randomly selected sample can differ from the population merely by chance; that difference alone does not establish systematic bias.

The website is voluntary response, with a sample entirely made of self-selected volunteers who may have unusually strong opinions. The entrance method is convenience sampling, selecting accessible people. Neither uses random chance to select neighborhood residents, so a large number does not remove the systematic selection concern.

Omitting non-smartphone residents is undercoverage: part of the population has no selection opportunity. Missing replies from selected residents is nonresponse: those people were selected but supplied no answer. Either can be important if affected residents differ on the studied variable.

The first question uses leading favorable wording. Replace it with a neutral question about support for the specified fee. The second self-report may overstate exercise to please the coach; confidential responses and a clear time period may reduce that pressure. Both concern recorded answers differing systematically from true opinions or behavior.

All app-poll respondents choose whether to participate, making it voluntary response. Riders with especially favorable or unfavorable experiences may be more motivated than indifferent riders, distorting satisfaction. The information does not establish one definite direction solely from self-selection.

Riders without smartphones are omitted from app invitations. Even among smartphone owners, riders who rarely open the app are less likely to see and join the poll. Both concern selection opportunity for parts of the target population.

“Excellent” leads respondents toward approval, and “easier and cheaper” combines two judgments that may differ. One neutral question is “Overall, how satisfied are you with the new bus timetable?” with clearly ordered response options. Separate questions about journey time and cost are also valid.

Selected riders who do not respond create nonresponse. Late-night riders are especially missing and face more cancellations, so they may be less satisfied than respondents. Their missing responses could make the estimated satisfaction proportion consistently too high relative to the all-rider parameter.

More self-selected replies can preserve the same volunteer and app-coverage distortions. Size does not introduce random chance or include omitted groups. A convenience survey of riders at the stop nearest city hall would also select easy-to-reach riders rather than the population by chance.

This is response bias in self-reported behavior: recorded missed-ride counts tend to be lower than true missed-ride counts. It concerns inaccurate answers, not the choice of sampled riders or missing selected responses.

Use a complete rider roster with non-app contact methods to address coverage. Contact selected people at varied times and follow up to reduce nonresponse. Use neutral, separate questions to address wording. These target different mechanisms; remaining missing replies, mistaken records, or inaccurate self-reports can still affect results.