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Table 3 Estimated prevalence of each of 22 key preselected behaviours in females in the best performing survey (WS-B2), before and after PSA weighting in five stages and in Natsal-3 for comparison, odds ratios and bias assessment

From: An evaluation of whether propensity score adjustment can remove the self-selection bias inherent to web panel surveys addressing sensitive health behaviours

  Proportions by weighting scheme and in Natsal-3 Odds ratios relative to Natsal-3 Bias3 relative to Natsal-3
Behaviour Age-sex PSA 1 PSA 2 PSA 3 PSA 4 PSA 5 Natsal-3 Age-sex PSA5 Age-sex PSA5
‘Binge’ drinks once a week or more1 0.098 0.099 0.095 0.098 0.090 0.092 0.118 0.81 0.76 small moderate
Both equally willing at first sex 0.791 0.789 0.788 0.794 0.800 0.805 0.821 0.83 0.90 small small
Contraception used at first sex 0.876 0.870 0.868 0.868 0.871 0.875 0.856 1.19 1.18 small small
First sex at about the right time 0.566 0.554 0.554 0.563 0.567 0.577 0.644 0.72 0.75 moderate moderate
Experience not all with opposite sex 0.245 0.233 0.223 0.218 0.207 0.192 0.159 1.72 1.26 large moderate
Had heterosexual oral sex in last year 0.705 0.714 0.717 0.720 0.739 0.745 0.770 0.71 0.87 moderate small
Had heterosexual anal sex in last year 0.166 0.168 0.168 0.164 0.172 0.169 0.154 1.09 1.12 small small
Sex without condom in last 4 weeks 0.789 0.797 0.799 0.798 0.794 0.793 0.800 0.93 0.96 small small
1+ same gender partners last 5 years 0.064 0.062 0.055 0.052 0.052 0.047 0.049 1.33 0.96 moderate small
Attended STI clinic in last 5 years 0.184 0.179 0.178 0.179 0.177 0.174 0.203 0.89 0.83 small small
Attended STI clinic in last year 0.060 0.057 0.056 0.056 0.058 0.056 0.085 0.69 0.64 moderate moderate
Ever STI diagnosis 0.172 0.176 0.175 0.173 0.163 0.158 0.188 0.90 0.81 small small
Ever taken illicit drugs 0.406 0.392 0.388 0.380 0.373 0.360 0.385 1.09 0.90 small small
Ever taken cannabis 0.368 0.353 0.351 0.344 0.339 0.327 0.355 1.06 0.88 small small
1+ new heterosexual partners last year 0.174 0.168 0.169 0.170 0.166 0.167 0.218 0.76 0.72 moderate moderate
0 heterosexual partners lifetime 0.059 0.058 0.055 0.057 0.053 0.054 0.045 1.33 1.21 moderate small
0 heterosexual partners last 5 years 0.099 0.094 0.090 0.090 0.084 0.082 0.064 1.61 1.31 moderate moderate
0 heterosexual partners last year 0.177 0.168 0.163 0.161 0.148 0.144 0.107 1.79 1.40 large moderate
Heterosexual sex 5+ occasions last 4 weeks 0.527 0.526 0.524 0.523 0.540 0.542 0.452 1.35 1.43 moderate moderate
Ever paid for heterosexual sex 0.147 0.155 0.157 0.152 0.150 0.146 0.148 0.99 0.98 small small
Had a sexual function problem in last year2 0.506 0.496 0.492 0.485 0.460 0.449 0.483 1.10 0.87 small small
Easy to talk to parent(s) about sex at age 14 0.149 0.148 0.145 0.146 0.154 0.154 0.252 0.52 0.54 large large
  1. 1. Defined as drinking 6+ units of alcohol; 2. Based on half the sample only; 3. Small bias is an odds ratio relative to Natsal-3 in the range 0.8–1.25, moderate bias is in the range 0.6–0.8 or 1.25–1.67, large bias otherwise