data = [
{ year: 1995, a_mean: 23, a_sd: 0.5, b_mean: 32, b_sd: 0.6 },
{ year: 1996, a_mean: 24, a_sd: 0.6, b_mean: 31, b_sd: 0.65 },
{ year: 1997, a_mean: 24.5, a_sd: 0.4, b_mean: 30.5, b_sd: 0.6 },
{ year: 1998, a_mean: 22, a_sd: 0.6, b_mean: 30, b_sd: 0.6 },
{ year: 1999, a_mean: 26, a_sd: 0.5, b_mean: 39.5, b_sd: 0.6 },
]